To see the other types of publications on this topic, follow the link: Films layer-by-layer.
Dissertations / Theses on the topic 'Films layer-by-layer'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Films layer-by-layer.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Schmidt, Daniel J. Ph D. Massachusetts Institute of Technology. "Engineering electroresponsive layer-by-layer thin films." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/62735.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references.
Electroresponsive layer-by-layer (LbL) polymer films and polymer nanocomposite films were investigated as model systems for electrically triggered drug delivery applications and "mechanomutable" surface coating applications. Two strategies were implemented in the design of these electroresponsive films: the use of redox-active, chargeshifting nanoparticles and the control over local pH utilizing the electrochemical reduction of dissolved oxygen. These strategies and the multiple materials systems explored are described below. Redox-active Prussian Blue (PB) nanoparticles exhibit multiple, stable oxidation states and can shift their charge in response to mild electric potentials. The inherently negatively charged particles may be self-assembled into LbL films along with positively charged polyelectrolytes. When the PB in an LbL film is oxidized to its neutral state, dissolution of the film occurs as cohesive ionic crosslinks are broken and excess charge in the film brings in ions and water for electroneutrality, which solubilize the film components. The release of the polyanion dextran sulfate and the small molecule antibiotic gentamicin sulfate were precisely controlled with an electric potential. When PB is reduced, the negative charge on the particle is doubled, which results in film swelling and a decrease in stiffness. In films comprising PB and linear polyethyleneimine, reversible thickness changes on the order of 5-10% and reversible elastic modulus changes on the order of 50% (between 3.40 GPa and 1.75 GPa) were observed. Employing the second strategy mentioned above, the local pH near an electrode surface may be increased to more basic values when dissolved oxygen is electrochemically reduced to hydroxide ions. In the first model system explored, hydrogen bonded (H-bonded) films comprising polyvinylpyrrolidone (PVPON) and tannic acid (TA), were dissolved at constant bulk pH by applying mild potentials (-0.25 V to -1.00 V vs. Ag/AgCl). The dissolution mechanism and kinetics could be tuned with the magnitude of the applied voltage and the concentration of dissolved oxygen. In the second model system explored, films comprising polyallylamine hydrochloride (PAH) and sulfonated polystyrene (SPS) were found to undergo reversible and dramatic swelling/deswelling transitions on the order of roughly 300 vol% and mechanical transitions on the order of 600-800% (shear modulus between 230 kPa and 1.9 MPa and loss modulus between 90 kPa and 620 kPa). This thesis contributes to the applied materials science branch of chemical engineering. New polymer and polymer nanocomposite thin films were developed that can be further engineered and incorporated into implantable drug delivery devices for electrically triggered drug delivery or incorporated into MEMS and microfluidic systems for flow control or biomedical applications. Furthermore, the model systems presented here open doors for fundamental work on the transport of electrons, ions, and water through these electroresponsive films and the implications of transport phenomena on the control over film dissolution and swelling responses.
by Daniel J. Schmidt.
Ph.D.
2
Jan, Chien Sy Jason. "Layer-by-layer assembly of electrically conductive polymer thin films." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/5979.
Full textAbstract:
Layer-by-layer (LbL) assembly was used to produce highly conductive thin films
with carbon black (CB) and polyelectrolytes. The effects of sonication and pHadjustment
of the deposition mixtures on the conductivity and transparency of deposited
films were studied. Drying temperature was also evaluated with regard to thin film
resistance. Sonication and oven drying at 70oC produced films with the lowest sheet
resistance (~ 1500 é/sq), which corresponds to a bulk resistivity of 0.2 éâÂÂ
cm for a 14-
bilayer film that is 1.3 üm thick. Increasing the pH of the PAA-stabilized mixture and
decreasing the pH of the PEI-stabilized mixture resulted in films with 70% transparency
due to thinner deposition from increased polymer charge density. Varying the number
of bilayers allows both sheet resistance and optical transparency to be tailored over a
broad range.
Variation of deposition mixture composition led to further reduction of sheet
resistance per bilayer. A 14 bilayer film, made from mixtures of 0.25wt% carbon black
in 0.05wt% PAA and plain 0.1wt% PEI, was found to have a sheet resistance of
approximately 325 é/sq. Bulk resistivity was not improved due to the film being 8 üm
thick, but this combination of small thickness and low resistance is an order of magnitude better than carbon black filled composites made via traditional melt or
solution processing. Applications for this technology lie in the areas of flexible
electronics, electrostatic charge dissipation, and electromagnetic interference shielding.
3
Higy, Christophe. "Polyelectrolyte conformation in layer-by-layer assembled nanoscale films." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE007/document.
Full textAbstract:
L’assemblage couche-par-couche permet de fabriquer des films multimatériaux aux propriétés variées présentant une structure stratifiée. Ce travail décrit les études structurelles des films multicouches de polyélectrolytes à l’aide de mesures de diffusion de neutrons.L’effet du vieillissement des films a été déterminé par réflectométrie des neutrons. Nous avons observé un léger tassement des films après 5 ans et une forte expansion après 15 ans.Nous avons aussi montré que le substrat et l’air en surface ont une influence sur la structure des couches proches des extrémités des films, conduisant à une structure inhomogène perpendiculairement à la surface.Nous avons finalement étudié la conformation des chaînes de polyélectrolytes dans les films multicouches ; nous avons déterminé que les chaînes de PSS dans des films préparés par trempage ont une conformation en pelotes aplaties, contrairement aux chaînes de polyélectrolytes en solution qui présentent une conformation sphériqueThe Layer-by-Layer assembly allows the build-up of multimaterial films with various properties showing a stratified structure. This work describes the structural strudies of multilayer films of polyelectrolytes with neutron scattering measurements.Ageing effect on films was determined by neutron reflectometry. We observed a slight shrink of the films after 5 years and a strong expansion after 15 years.We also showed that the proximity of the substrate and the air at the surface have an influence on the structure of the layers at the extremities of the films, leading to an inhomogeneous structure perpendicularly to the surface.Finally, we studied the conformation of polyelectrolyte chains in the multilayer films ; we determined that PSS chains in dipped films have a flattened coil conformation, whereas the polyelectrolyte chains in solution have a spherical conformation
4
Chance, Brandon Scott. "Layer-by-layer assembly on polyethylene films via "click" chemistry." Thesis, [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1252.
Full text
5
Dronov, Roman. "Multi-component protein films by layer-by-layer : assembly and electron transfer." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1728/.
Full textAbstract:
Electron transfer phenomena in proteins represent one of the most common types of biochemical reactions. They play a central role in energy conversion pathways in living cells, and are crucial components in respiration and photosynthesis. These complex biochemical reaction cascades consist of a series of proteins and protein complexes that couple a charge transfer to different forms of chemical energy. The efficiency and sophisticated optimisation of signal transfer in these natural redox chains has inspired engineering of artificial architectures mimicking essential properties of their natural analogues.
Implementation of direct electron transfer (DET) in protein assemblies was a breakthrough in bioelectronics, providing a simple and efficient way for coupling biological recognition events to a signal transducer. DET avoids the use of redox mediators, reducing potential interferences and side reactions, as well as being more compatible with in vivo conditions. However, only a few haem proteins, including the redox protein cytochrome c (cyt.c), and blue copper enzymes show efficient DET on different kinds of electrodes.
Previous investigations with cyt.c have mainly focused on heterogeneous electron transfer of monolayers of this protein on gold. An important advance was the fabrication of cyt.c multilayers by electrostatic layer-by-layer self-assembly. The ease of fabrication, the stability, and the controllable permeability of polyelectrolyte multilayers have made them particularly attractive for electroanalytical applications. With cyt.c and sulfonated polyaniline it was for the first time possible that fully electro-active multilayers of the redox protein could be prepared.
This approach was extended to design an analytical signal chain based on multilayers of cyt.c and xanthine oxidase (XOD). The system does not need an external mediator but relies on an in situ generation of a mediating radical and thus allows a signal transfer from hypoxanthine via the substrate converting enzyme and cyt.c to the electrode.
Another kind of a signal chain is based on assembling proteins in complexes on electrodes in such a way that a direct protein-protein electron transfer becomes feasible. This design does not need a redox mediator in analogy to natural protein communication. For this purpose, cyt.c and the enzyme bilirubin oxidase (BOD, EC 1.3.3.5) are co-immobilized in a self-assembled polyelectrolyte multilayer on gold electrodes. Although these two proteins are not natural reaction partners, the protein architecture facilitates an electron transfer from the electrode via multiple protein layers to molecular oxygen resulting in a significant catalytic reduction current.
Finally, we describe a novel strategy for multi-protein layer-by-layer self-assembly combining cyt.c with an enzyme sulfite oxidase (SOx) without use of any additional polymer. Electrostatic interactions between these two proteins with rather separated pI values during the assembly process from a low ionic strength buffer were found sufficient for the layer-by-layer deposition of the both biomolecules.
It is anticipated that the concepts described in this work will stimulate further progress in multilayer design of even more complex biomimetic signal cascades taking advantage of direct communication between proteins.Elektronentransferphänomene in Proteinen stellen den häufigsten Typ biochemischer Reaktionen dar. Sie spielen eine zentrale Rolle bei der Energieumwandlung in der Zelle und sind entscheidende Komponenten in der Atmung und Photosynthese. Diese komplexen Kaskaden biochemischer Reaktionen setzen sich aus einer Reihe von Proteinen und Proteinkomplexen zusammen, die den Energietransfer an verschiedene Formen chemischer Energie koppeln. Die große Effektivität und Selektivität des Signaltransfers in diesen natürlichen Redoxketten war Vorbild für die Entwicklung künstlicher Architekturen, die die wesentlichen Eigenschaften ihrer natürlichen Analoga nachahmen. Die Implementierung des direkten Elektronentransfers (DET) von Proteinen mit Elektroden war ein Durchbruch im Bereich der Bioelektronik. Sie lieferte einen einfachen und effizienten Weg für das Koppeln biologischer Erkennungsereignisse an einen Signalumwandler. Durch den DET können Redoxmediatoren vermieden und damit potentielle Grenzflächen und Nebenreaktionen reduziert werden. Ebenso wird damit die Kompatibilität für in vivo Bedingungen erhöht. Jedoch zeigen nur einige Hämproteine wie das Redoxprotein Cytochrom c (Cyt c) und blaue Kupferproteine einen effizienten DET auf verschiedenen Elektrodentypen. Bisherige Untersuchungen mit Cyt c konzentrierten sich hauptsächlich auf den heterogenen Elektronentransfer von Monoschichten dieses Proteins auf Gold. Ein wichtiger Fortschritt war die Herstellung von Cyt c Multischichten durch die elektrostatische Layer-by-Layer-Technik. Die einfache Herstellung, die Stabilität sowie die kontrollierbaren Permeationseigenschaften von Polyelektrolyt-Multischichten machte sie besonders attraktiv für elektroanalytische Anwendungen. So gelang es auch zum ersten Mal vollständig elektroaktive Multischichten aus Cyt c und Polyanilinsulfonsäure zu präparieren. Dieser Ansatz wurde hier erweitert, um eine analytische Signalkette auf der Basis von Multischichten aus Cyt c und Xanthinoxidase zu entwerfen. Das System bedarf keinen externen Mediator, es hängt jedoch von der in situ Generierung eines vermittelnden Radikals ab und erlaubt daher einen Signaltransfer von Hypoxanthin über ein substratumwandelndes Enzym und Cyt c zur Elektrode. Eine andere Art von Signalketten basiert auf der Assemblierung von Proteinen in Komplexen auf Elektroden in solcher Art und Weise, daß ein direkter Protein-Protein-Elektronentransfer möglich wird. Dieser Ansatz benötigt keinen Redoxmediator in Analogie zu Beispielen aus dem biologischen Signaltransfer. Zu diesem Zweck werden Cyt c und das Enzym Bilirubinoxidase mit einem selbst-assemblierenden Polyelektrolyten auf einer Goldelektrode koimmobilisiert. Obwohl diese zwei Proteine keine natürlichen Reaktionspartner sind, unterstützt die Protein-Architektur einen Elektronentransfer von der Elektrode über mehrere Proteinschichten zu molekularem Sauerstoff und ergibt einen signifikanten katalytischen Reduktionsstrom. Schließlich wird eine neue Strategie beschrieben für eine Selbstassemblierung von Proteinen ohne zusätzlichen Polyelektrolyten - am Beispiel der Kombination von Cyt c mit Sulfitoxidase. Es stellte sich heraus, daß die elektrostatische Wechselwirkung zwischen diesen zwei Proteinen mit ziemlich weit voneinander entfernt liegenden pI-Werten während des Assemblierungsprozesses durch einen Puffer mit geringer Ionenstärke ausreicht um die beiden Biomoleküle nach dem Layer-by-Layer-Prinzip auf einer Elektrode abzuscheiden. Es wird erwartet, daß das entwickelte Konzept von Multiprotein-Assemblaten auf Elektroden weitere Fortschritte bei dem Entwurf von Multischichten und sogar noch komplexeren biomimetischen Signalkaskaden anregen wird und dabei der Vorteil der direkten Kommunikation zwischen Proteinen genutzt wird.
6
Dziedzic, Tomasz. "Electrochemistry of layer-by-layer films containing redox active MnO₂ nanoparticles." Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1798480871&sid=2&Fmt=2&clientId=18949&RQT=309&VName=PQD.
Full text
7
Yoo, Dongsik. "Functional multilayer organic thin films fabricated by layer-by-layer sequential adsorption technique." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43366.
Full text
8
Mak, Wing Cheung. "The applications of layer-by-layer technology in bioengineering and bioanalytics /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?BIEN%202004%20MAK.
Full text
9
Cai, Li-Rong. "Organic-inorganic layer-by-layer self-assembled multilayer films : preparation, characterization and applications /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202004%20CAI.
Full text
10
DeLongchamp, Dean M. (Dean Michael) 1975. "Engineering the electrochromism and ion conduction of layer-by-layer assembled films." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29995.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003.Includes bibliographical references.
This work applies the processing technique of layer-by-layer (LBL) assembly to the creation and development of new electrochemically active materials. Elements of the thin-film electrochromic cell were chosen as a particular focus for LBL fabrication. Layer-by-layer assembly is the ideal processing tool to tailor the electrochemical systems within electrochromic cells because modulating processing conditions can greatly impact the nanoscale composition and morphology of the resultant films. For the first time, this control was used to: 1) intelligently design electrochromic LBL assembled composite films that facilitated ion motion for faster switching and exhibited enhanced or shifted coloration, 2) combine multiple electrochromic materials into novel LBL assembled composites with even higher contrast, faster switching, and multiple colored states, and finally 3) develop and optimize several LBL assembled polymer electrolyte films that display high ionic conductivity and sound mechanical integrity. Electrochromic cell elements were chosen not only for their undeveloped commercial potential, but also because they incorporate multifunctional material systems with alternative applications. Studies of LBL fabrication and the operation of electrochromic cells provide insight into intermolecular interactions, internal and external film interfaces, thin film electrochemistry, and charged species mobility in polymer solids. First investigated was the capability of LBL assembly to alter the properties of electrochromic films by varying molecular blending.
(cont.) The electrochromophores for this investigation were appropriated from all corners of the materials spectrum, including discrete electrochromic polymers, conjugated polymers, soft colloidal suspensions, and inorganic particle dispersions. In each system, the influence of assembly conditions and film composition was elucidated; in particular systems the hydrophobicity, acidity, and morphology of the films were found to impact the electrochemistry and optical character of the films, providing a means to modulate these properties by directing LBL assembly design choices. Because of the high uniformity and thickness control allowed by LBL assembly, the contrast and switching performance of all LBL assembled electrochromic films were in general superior to those of films containing the same electrochromophores fabricated by other methods. One particularly promising system involved novel LBL assembled films containing the same electrochromophores fabricated by other methods. One particularly promising system involved novel LBL assembled films containing electrochromic metal hexacyanoferrate nanocrystals of the Prussian blue family. These films displayed fast and deep coloration; synthetic nanocrystal variation extended absorbance over a broad spectral range so that these inorganic/polymer composite films could potentially be considered as elements in a full-color switchable CMYK display. The power of the LBL assembly technique was leveraged further with the successful fabrication of "dual electrochrome" electrodes ...
by Dean M. DeLongchamp.
Ph.D.
11
DeWitt, David Michael 1972. "Studying and controlling chromophore orientation in polyelectrolyte layer-by-layer thin films." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29278.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2002.Includes bibliographical references.
Many properties such as electrical conductivity, liquid crystallinity, and optical properties depend on specific molecular orientation. Currently, this orientation is achieved using either inorganic crystals or rigorously processed organic materials. This thesis studied a film assembly technique that provides a mechanism for aligning polymeric materials as films are assembled. This eliminates the need for a post-processing alignment step and allows easier film construction. The fabrication technique for the polymeric thin films is layer-by-layer (LBL) electrostatic assembly. This technique takes advantage of the electrostatic attraction between oppositely charged polyelectrolytes to assembly films. For example, a polyanion and polycation are dissolved in separate aqueous solutions at a given pH and salt concentration. A charged substrate is immersed into one solution, rinsed with water, and immersed in the other solution. This cycle is repeated to assemble films. Typically, the polyelectrolytes in these films are randomly arranged; however, a few researchers have demonstrated that ordered films could be assembled with the LBL technique. We investigated the driving force of this order and how to control it by studying the processing parameters, polyelectrolytes, and surfaces used to assemble ordered LBL films. For the processing study, two side-chain chromophoric polyanions were used. One, PolyS 119, contained sulfonic acid groups while the other, PAZO, contained carboxylic acid groups. These were assembled with four polyamines. The pH of the polyanion solutions was varied to observe its effect on chromophore orientation. Chromophore orientation was measured by FTIR and UV/isible spectroscopy.
(cont.) From these studies it was determined that stronger electrostatic attraction leads to more orientation; thus, orientation can be controlled by adjusting the strength of the attraction using different pH values since the ionization of the polyelectrolytes changes with the pH. The salt concentration of the solutions has a more subtle effect. The salt can change the ionization of polyelectrolytes in solution, which changes their ionization and influences the electrostatic attraction. Again, it was demonstrated that chromophore orientation could be adjusted by changing the solution conditions. LBL film structure is influenced by the processing conditions as well as the chemical structure of the polyelectrolytes. Since we studied how processing parameters affect orientation, we also wanted to determine the role of chemical structure. Other research on liquid crystals has shown that the spacer length between the side- and main polymer chain affects rigid side-chain orientation. For this study, a series of polymers of varying spacer length were synthesized. These were then assembled with the same four polyamines used in the previous studies. More orientation with increased spacer length was observed indicating that chromophores with longer spacers have more freedom from the main polymer chain and this allows more orientation. This effect is independent of the polyamine used to assemble the films. Another chemical struture study was changing the location of the charged group from the side-chain chromophores to the polymer main-chain ...
by David Michael DeWitt.
Ph.D.
12
Jain, Vaibhav. "Applications of Layer-by-Layer Films in Electrochromic Devices and Bending Actuators." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28907.
Full textAbstract:
This thesis presents work done to improve the switching speed and contrast performance of electrochromic devices. Layer-by-Layer (LbL) assembly was used to deposit thin electrochromic films of materials ranging from organic, inorganic, conducting polymers, etc. The focus was on developing new materials with high contrast and long lifecycles. A detailed switching-speed study of solid-state EC devices of already-developed (PEDOT (Poly(3,4-ethylenedioxythiophene)), polyviologen, inorganic) materials and some new materials (Prodot-Sultone) was performed. Work was done to achieve the optimum thickness and number of bilayers in LbL films resulting in high-contrast and fast switching. Device sizes were varied for comparison of the performance of the lab-made prototype device with the commercially available â small pixelâ size displays. Symmetrical EC devices were fabricated and tested whenever conducting polymers are used as an EC material. This symmetrical configuration utilizes conducting polymers as an electroactive layer on each of two ITO-coated substrates; potential is applied to the two layers of similar conducting polymers and the device changes color from one redox state to another. This method, along with LbL film assembly, are the main factors in the improvement of switching speed results over already-published work in the literature. PEDOT results show that EC devices fabricated by LbL assembly with a switching speed of less than 30 ms make EC flat-panel displays possible by adjusting film thickness, device size, and type of material. The high contrast value (84%) for RuP suggests that its LbL films can be used for low-power consumption displays where contrast, not fastest switching, is the prime importance.
In addition to the electrochromic work, this thesis also includes a section on the application of LbL assembly in fabricating electromechanical bending actuators. For bending actuators based on ionic polymer metal composites (IPMCs), a new class of conductive composite network (CNC) electrode was investigated, based on LbL self-assembled multilayers of conductive gold (Au) nanoparticles. The CNC of an electromechanical actuator fabricated with 100 bilayers of polyallylamine hydrochloride (PAH)/Au NPs exhibits high strain value of 6.8% with an actuation speed of 0.18 seconds for a 26 µm thick IPMC with 0.4 µm thick LbL CNCs under 4 volts.Ph. D.
13
Merindol, Rémi. "Layer-by-layer assembly of strong bio-inspired nanocomposites." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE015/document.
Full textAbstract:
Les performances exceptionnelles des composites naturels comme la nacre ou le bois émergent de l’arrangement précis d’éléments souples et rigides à l’échelle nanométrique. L’assemblage couche-par-couche permet la fabrication de films avec un contrôle nanométrique de l’organisation et de la composition. Ce travail décrit l’assemblage et les propriétés de nouveaux nano-composites contenant des nano-renforts 1-D (fibrilles de cellulose) et 2-D (plaquettes d’argile). Nous avons combiné les argiles avec une matrice extrêmement souple de poly(diméthylsiloxane) dans une architecture lamellaire imitant celle de la nacre. Nous avons étudié des composites à base de fibrilles de cellulose aléatoirement orientées dans le plan, puis alignées dans une direction pour mieux imiter les parois cellulaires du bois. Les propriétés mécaniques de ces composites bio-inspirés égalent ou surpassent celles de leurs homologues naturels, tout en étant transparents et dans certains cas auto-réparantsNatural materials such as nacre or wood gain their exceptional mechanical performances from the precise organisation of rigid and soft components at the nano-scale. Layer-by-layer assembly allows the preparation of films with a nano-scale control over their organisation and composition. This work describes the assembly and properties of new nano-composites containing 1-D (cellulose nano-fibrils) and 2-D (clay nano-platelets) reinforcing elements. The clay platelets were combined with an extremely soft matrix (poly(dimethylsiloxane)) to mimic the lamellar architecture of nacre. Cellulose based composites with a random in plane orientation of the fibrils were studied first, later we aligned the fibrils in a single direction to mimic further the cell wall of wood. The mechanical properties of these bio-inspired composites match or surpass those of their natural counterparts, while being transparent and in one case self-repairing
14
Freitas, Ivo Bernardi de 1989. "Filmes crescidos pela técnica layer-by-layer (LbL) de nanopartículas inorgânicas e seus estudos fotoeletroquímicos." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248364.
Full textAbstract:
Orientador: Ana Flávia NogueiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-22T23:28:35Z (GMT). No. of bitstreams: 1 Freitas_IvoBernardide_M.pdf: 1962051 bytes, checksum: f313acbe4cbb5d4065bb7bb26e42e3ac (MD5) Previous issue date: 2013
Resumo: Neste trabalho foram estudados filmes finos multicamadas baseados em nanopartículas inorgânicas e um polieletrolito inerte, depositados pela técnica layer-by-layer (LbL). O trabalho está dividido em três partes: 1) Síntese e caracterização de nanopartículas de CdSe; 2) Montagem de filmes LbL baseados no cloreto de poli(diallildimetilamônio) (PDDA) e nanopartículas de CdSe e TiO2; e 3) Estudos fotoeletroquímicos dos filmes. As nanopartículas sintetizadas foram caracterizadas por espectroscopia de absorção no ultravioleta-visível (UV-vis), espectroscopia de fluorescência, microscopia eletrônica de alta resolução (HRTEM) e difração de raios-X (DRX). As partículas sintetizadas não apresentaram a mesma qualidade daquelas reportadas pela literatura, apresentando grande número de defeitos e larga distribuição de tamanhos. Como não foi possível a separação adequada de nanopartículas de diferentes tamanhos, optou-se por dar continuidade ao trabalho com somente um tamanho obtido. Foram fabricados filmes contendo TiO2 e PDDA, filmes contendo CdSe e PDDA e filmes contendo TiO2, CdSe e PDDA. Estes foram caracterizados por espectroscopia de absorção no UV-vis, espectroscopia de fluorescência, microscopia de força atômica (AFM) e espectroscopia Raman. Os filmes apresentaram um crescimento linear a cada bicamada realizada. Visando melhorar a qualidade dos filmes fabricados um tratamento com brometo de hexadeciltrimetilamonio (CTAB) foi utilizado. Os filmes de nanopartículas de CdSe com tratamento apresentaram uma quantidade de defeitos menor em relação aos filmes sem tratamento. Os fotoeletrodos foram caracterizados por medidas de fotocorrente em função do tempo (fotocronoamperometria). Os filmes contendo TiO2 e PDDA apresentaram valores de fotocorrente, entre 2 e 50 mA cm, exibindo comportamento de semicondutor do tipo-n. Ja os filmes contendo CdSe e PDDA apresentaram valores baixos de fotocorrente (2 mA cm). Mesmo após a realização do tratamento com CTAB e a incorporação de nanopartículas de TiO2 nos filmes não observou-se uma significante alteração nestes valores
Abstract: In this work, multilayered thin films based on inorganic nanoparticles and an inert polyelectrolyte deposited by the layer-by-layer technique were studied. The work was divided in three parts: 1) Synthesis and characterization of CdSe nanoparticles; 2) Assembly of LbL films based in poly(diallyldimethylammonium chloride) (PDDA) , CdSe and TiO2 nanoparticles; 3) Photoelectrochemical studies of the films. The nanoparticles synthetized were characterized by absorption spectroscopy, fluorescence spectroscopy, high resolution electron microscopy (HRTEM) and X-ray diffraction. The synthesized nanoparticles didn¿t show the same quality of those reported in literature. They presented a large number of defects and a broad size distribution. As it was not possible to obtain nanoparticles of different sizes, we decided to continue the work with only one nanoparticle size. Films were fabricated using CdSe and PDDA, TiO2 and PDDA, and CdSe, PDDA and TiO2. They were characterized by absorption spectroscopy, fluorescence spectroscopy, atomic force microscopy (AFM) and Raman spectroscopy. The films showed a linear increase to each bilayer performed. In order to improve the films quality containing CdSe nanoparticles, a treatment using hexadecyltrimethylammonium bromide (CTAB) was performed. As a result, the treated films showed a smaller number of defects compared to the films without treatment. The photoelectrodes were characterized by measurements of photocurrent versus time (photochronoamperometry). The films containing TiO2 and PDDA showed appreciable values of photocurrent, between 2 and 50 mA cm, exhibiting an n-type semiconducting behavior. However, the films containing CdSe and PDDA showed low photocurrent values (2 mA cm). Even after the treatment with CTAB and the incorporation of the TiO2 nanoparticles in the films, no remarkable improvement in the photocurrent values was observed
Mestrado
Quimica Inorganica
Mestre em Química
15
Pontes, Ricardo Scudeler. "Adsorção e fluorescência em filmes automontados de polianilina (PAN) e poli(p-fenileno vinileno)(PPV)." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-07112013-171013/.
Full textAbstract:
A técnica de automontagem [Self-Assembly (SA)] tem sido largamente empregada na fabricação de estruturas supramoleculares de polímeros condutores que requerem controle molecular. O paradigma implícito no método de automontagem é a adsorção espontânea de camadas carregadas com cargas opostas, conduzindo assim a um filme de multicamadas formado pela alternância de policátions e poliânions. Nesta dissertação, são empregados dois tipos de polímeros conjugados e seus derivados que são identificados por suas famílias, que são a da polianilina (PAn) e a do poli(pfenileno vinileno) (PPV). São enfatizados os processos de adsorção para as polianilinas e precursores do PPV, propondo-se um mecanismo de adsorção não autolimitada sustentado por condições de não equilíbrio. O processo não autolimitado comprova que a adsorção pode ser controlada por outras interações que não a eletrostática, como as pontes de hidrogênio que são comuns nas polianilinas, e/ou por interações típicas de dispersões coloidais, visto que os polímeros se agregam em solução. Este novo método pode ter grande impacto na fabricação de estruturas supramoleculares porque podem ser obtidos filmes espessos de uma única camada com controle em nível molecular. A desvantagem deste método está na obtenção de filmes não uniformes, propriedade que ainda não é adequadamente controlada. A investigação da formação de filmes de múltiplas camadas e dos processos de fluorescência para filmes de bicamadas e não autolimitados é apresentada e discutida em função dos trabalhos da literatura. Finalmente, são correlacionados os processos de adsorção e a fluorescênciaThe self-assembly (SA) technique has been widely used for producing supramolecular structures fi-om conducting polymers, in which molecular control may be achieved. The paradigm implicit in the SA method is the spontaneous adsorption of oppositely charged layers, thus leading to a multilayer film containing polycations alternated with polyanions. In this dissertation, two types of polymer are employed in the fabrication of SA films, namely polyanilines and poly(p-phenylene vinylenes) (PPVs). For the polyanilines, emphasis was placed in the adsorption processes, where it is proposed that a non-self-limiting process may be achieved if adsorption is carried out under non-equilibrium conditions. A non-self-limiting process is proof that adsorption is not entirely controlled by electrostatic interactions, but may also depend on H-bonding which is very efficient in polyanilines and on interactions typical of colloid dispersions as the polymers aggregate while in solution. This nove1 method may have a large impact in the fabrication of supramolecular structures because much thicker films may be obtained in a single layer. The disadvantage of this method, however, lies in the fabrication of non-uniform films which cannot be controlled adequately. The investigation of the fabrication of multilayers and of fluorescence processes in films built with bilayers and via non-self-limiting adsorption is presented and discussed in terms of work published in the literature. Finally, the processes of adsorption and fluorescence are correlated
16
Mujica, Randy. "Layer-by-Layer assembly of nanocellulose composite films with bio-inspired helicoidal superstructures." Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE011.
Full textAbstract:
Les propriétés optiques et mécaniques remarquables des matériaux naturels sont souvent associées à la complexité de leurs structures hiérarchiques. L’une des plus complexes est la structure hélicoïdale, constituée de plusieurs couches de fibres alignées dont l’orientation tourne entre les couches voisines. Cette microstructure, dite de Bouligand, est associée à la résistance aux chocs accrue de la carapace de certains crustacés ainsi qu’à la réflexion préférentielle de la lumière polarisée circulaire de certains fruits et insectes. Dans ce travail, nous avons fabriqué des films minces bio-inspirés complexes composés de nanofibrilles de cellulose et de poly(vinylamine) en utilisant l'approche couche-par-couche (LbL) et la pulvérisation à incidence rasante (GIS), une méthode permettant de contrôler l'alignement dans le plan de nano-objets anisotropes comme les nanofibrilles de cellulose. Nous avons démontré la possibilité de contrôler de façon indépendante la direction de l'alignement de chaque couche de cellulose. Ainsi, nous avons pu préparer des films minces avec une orientation unidirectionnelle, croisée ou hélicoïdale des nanofibrilles de cellulose, ce qu’il n’est pas possible de faire avec d’autres procédés de fabrication. Les propriétés optiques de ces films ont été caractérisées par dichroïsme circulaire et ellipsométrie spectroscopique à matrice de Mueller. Nous avons observé que la réponse chirale des films hélicoïdaux est contrôlée par le sens de rotation, le pas de l’hélice et le nombre de couches avant rotation. Les propriétés mécaniques de ces films ont été étudiées par différentes méthodes de nanoindentation. La méthodologie de fatigue par nano-contact a montré une ductilité accrue des films unidirectionnels et hélicoïdaux, qui peut être indirectement liée à une absorption accrue de l'énergie de ce matériau lors des sollicitations en raison de sa structure interneThe remarkable optical and mechanical properties of natural materials are often associated with the complexity of their hierarchical structures. One of the most complexes is the helical structure which consists of several layers of unidirectionally aligned fibers whose orientation rotates with respect to their neighboring layers. This so-called Bouligand microstructure is responsible for the enhanced impact resistance of the shell of some crustaceans as well as the preferential reflection of circularly polarized light of certain fruits and insects. Here, we fabricated complex bio-inspired thin films made of cellulose nanofibrils and poly(vinylamine) using the layer-by-layer (LbL) approach and grazing incidence spraying (GIS), a method allowing to control the in-plane alignment of anisotropic nano-objects like cellulose nanofibrils. We demonstrated the independent direction of alignment of each cellulose layer, which allowed the preparation of thin films with well-defined internal structures, namely, unidirectional, cross-ply or helical arrangement of the reinforcing nanofibrils, which is impossible to achieve by any other fabrication process. The optical properties of these films were characterized by circular dichroism (CD) and by Mueller matrix ellipsometry. The chirality observed for helicoidal films is controlled by the rotation direction, the pitch, and the number of layers. The mechanical properties of these cellulose-based films were studied by various nanoindentation methods. A nano-contact fatigue methodology showed an increased ductility of the unidirectional and helicoidal films, which can be indirectly related to enhanced absorption of energy of this material owing to their internal structure
17
Chen, Jing. "Novel H-bond donor polymers for layer-by-layer self-assembly multilayered films." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0087/document.
Full textAbstract:
Ce travail est consacré à la synthèse de nouveaux polymères donneurs de liaison Hydrogène et à leur utilisation comme partenaire dans la construction de nouveaux films multicouches préparés par le procédé d’élaboration en couche-par-couche (LbL). Plus particulièrement, une nouvelle réaction impliquant des mercaptoalcools non protégés et le poly(2,3,4,5,6-pentafluorostyrène) (PPFS) a été développé et appliquée à la synthèse de nouveaux polymères donneurs de liaisons H. Ce couplage régiosélectif et chimiosélectif de type « click » avec un thiol hétérofonctionnel peut être utilisée pour préparer une bibliothèque de polymères qui diffèrent de par leur degré de substitution (DS) et/ou leur fonctionnalité en groupements associatifs. Le contrôle de ces paramètres structuraux permet de moduler leur force d’interactions avec des partenaires accepteurs de liaison H variés, comme la poly(4-vinyl pyridine) (P4VP), le poly(acrylate de n-butyle) (PBA) et le poly(oxyde d'éthylène) (PEO), de telle façon que tous les types de mélanges binaires (mélange non miscible, partiellement ou totalement miscible, ou complexe interpolymère) peuvent être obtenus. Ensuite, les dérivés de PPFS donneurs de liaisons H ont été utilisés en partenariat avec le P4VP pour élaborer avec succès de nouveaux films multicouche dont la force motrice est l’établissement de liaisons H. L'influence de nombreux paramètres relatifs à la structure des polymères donneurs (DS, structure chimique du groupement associatif), au type de modification chimique subie par le substrat sur lequel est élaboré le film multicouche (monocouche auto-assemblée vs. polymère greffée en conformation de type brosse) ou encore des paramètres expérimentaux liés aux conditions de dépôt (concentration des solutions de dépôt, nature du partenaire adsorbé en premier) a été étudiée. Plus particulièrement, le mécanisme de croissance ainsi que les caractéristiques de surface du film ont été évaluésThis work deals with the design of novel hydrogen-bond donor polymers and their use as partner in new tailor-made multilayered films prepared by the layer-by-layer (LbL) process. In this context, a novel regioselective and chemoselective “click-type” reaction of unprotected mercaptoalcohols onto poly(2,3,4,5,6-pentafluoro-styrene) (PPFS) has been developed, and applied to the synthesis of new hydroxylated H-bond donor polymers. This coupling with heterofunctional thiol is used to prepare a library of polymers differing in the degree of substitution (DS) and/or functionality. The fine control of these parameters makes it possible to tune their interaction ability with various acceptor polymers such as poly(4-vinyl pyridine) (P4VP), poly(n-butyl acrylate) (PBA) and poly(ethylene oxide) (PEO), such that all possible scenarios (immiscible blend, partially or totally miscible blend or interpolymer complex) can be achieved. Subsequently, the resulting H-bond donor polymers (PPFS derivatives) were used to successfully build-up multilayered films with using P4VP as partner via layer-by-layer (LbL) through the dip deposition process. The influence of various parameters related to structure of the partners (DS, nature of the PPFS derivatives), the chemical structure of the surface onto which the film is built-up (self-assembled monolayer vs. polymer brush) and the deposition process (concentration of deposition solutions, nature of the first deposited partner) was in-depth evaluated, on both the growth mechanism and on the surface features of the multilayered films
18
Guzy, Matthew Thomas. "Organic Self-Assembled Layer-by-Layer Thin Films for Second-Order Nonlinear Optics." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28852.
Full textAbstract:
Layer-by-layer deposition techniques were used to fabricate films with second order nonlinear optical (NLO) properties. These materials are key to the development of electro-optic modulators used in fiber optic communication systems. Performance benefits and lower manufacturing costs are driving the development of organic NLO materials as replacements for inorganic crystalline materials such as lithium niobate.
The layer-by-layer deposition technique in which polyelectrolytes are deposited on a surface by electrostatic effects is called the Ionically Self-Assembled Monolayer or ISAM method. The role of the optically inactive polycation's structure on deposition and chromophore orientation was studied by fabricating films with several different polycations. While the specific interactions responsible for chromophore orientation in ISAM films remains unclear, hydrogen bonding and electrostatic effects are ruled out as the sole sources of orientation. The highest values of &967;(2) were observed under pH conditions that resulted in flat and thin layers. The relationship between pH and the optical homogeneity of the film was also explored. Deposition of polymers under pH conditions in which the polymer chains were aggregated in solution results in films that are not suitable for use in devices.
In this work, a new layer-by-layer deposition technique was developed. Coined hybrid deposition, it relies on covalent bonds and electrostatic interactions for film fabrication. Optically inactive polyamines were used as sources of positive charges and as binding sites with optically active low molecular weight chromophores functionalized with a reactive triazine ring and negative charged sulfonate groups. Polar ordering of the chromophores was obtained when the deposition was done under conditions in which covalent bonding was the preferred attachment mechanism for the chromophore molecules. pH conditions in which electrostatic attachment dominated resulted in poorer orientation. The effect of adding ionic salts to the dye solutions was studied, with hopes of increasing the chromophore density in the film by shielding inter-dye electrostatic repulsions. A linear relationship in deposited amount, as characterized by absorbance/bilayer, was observed as the salt concentration was increased. Little effect on &967;(2) was observed for films made with the as-received Procion Red MX-5B chromophore. However, films fabricated from purified Procion Brown MX-GRN showed a definite dependence on added salt. Exceptional &967;(2) values were obtained for Procion Brown films deposited using 0.5 M NaCl and PAH. The importance of depositing from non-aggregated solutions was again highlighted, as films made with the less soluble Procion Orange were significantly less homogeneous than those made from Procion Red and Procion Brown which were highly soluble. The role of polycation structure on the deposition and orientation of Procion Brown and Red was examined.Ph. D.
19
Storti, Felipe Chagas [UNESP]. "Estudo da arquitetura molecular de filmes layer-by-layer de ftalocianina tetrasulfonada de cobre." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/88497.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:23:30Z (GMT). No. of bitstreams: 0
Previous issue date: 2008-11-19Bitstream added on 2014-06-13T18:09:41Z : No. of bitstreams: 1
storti_fc_me_bauru.pdf: 1104117 bytes, checksum: f3374b86db01b726a613c1cc13d060e9 (MD5)Nesta dissertação é apresentado um estudo envolvendo a arquitetura molecular (crescimento controlado, morfologia e organização molecular) de filmes Layer-by-Layer (LbL) contendo ftalocianina tetrasulfonada de cobre (CuTsPc). Inicialmente foram realizados estudos sobre a cinética de crescimento desses filmes para determinação do tempo de adsorção do material no substrato. Uma vez determinado este tempo, filme LbL foram fabricados utilizando soluções catiônica de poli(alilamina) hidroclorada - PAH) e aniônica de CuTsPc. Os filmes de PAH/CuTsPc foram produzidos de forma manual e utilizando um braço mecânico em valores de pHs 2,5; 5,5 e 8,5 sendo então caracterizados por espectroscopia eletrônica via absorção na região do ultravioleta-visível (UV-Vis), espectroscopia vibracional via espalhamento Raman e absorção na região do infravermelho com transformadora de Fourier (FTIR) e microscopias óptica e força atômica (AF,A). A espectroscopia de absorção na região do UV-Vis foi utilizada para acompanhar o crescimento do filme LbL assim como investigar a presença de agregados. A técnica de FTIR permitiu investigar as interações entre o PAH e a CuTsPc e determinar a organização molecular comparando filme LbL e cast. O acoplamento entre microscópio óptico e espectrógrafo Raman (técnica microRaman) possibilitou analisar a morfologia do filme LbL em escala micrométrica combinando informações ópticas e químicas. A morfologia do filme LbL em escala nanométrica foi investigada utilizando-se AFM. Foi observado que os filmes crescidos mecanicamente são mais espessos em relação aos crescidos manualmente, além de apresentarem maior rugosidade. Ainda em termos morfológicos, os filmes crescidos mecanicamente apresentam uma maior quantidade de agregados, porém, menores em termos de diâmetro médio, tanto em escala nano como micrométrica...
This dissertation presents a study involving the molecular architecture (controlled growth, morphology, and molecular organization) of layer-by-layer (LbL) films containing copper phthalocyanine tetrasulfonated (CuTsPc). Initially, the studies were performed on the kinetics of growth of these films to determine the time of adsorption of the material on the substrate. Once determined this time, LbL films were produced by using solutions of cationic poly (hydrochloric alilamina - PAH) and anionic CuTsPc. The films of PAH / CuTsPc were produced either manually or using a mechanical arm in pH values of 2.5, 5.5, and 8.5, and then characterized by electron spectroscopy via absorption in the ultraviolet-visible (UV-Vis), vibrational spectroscopy by Raman scattering and absorption in the infrared region with Fourier transform infrared (FTIR) and optical microscopy and atomic force microscopy (AFM). The absorption spectroscopy in the UV-Vis was used to follow the growth of the LbL film and to investigate the presence of aggregates. The FTIR technique allowed investigatin the interactions between the PAH and CuTsPc and determining the molecular organization comparing LbL films and cast. The coupling between optical microscope and Raman spectrograph (micro-Raman technique) allowed analyzing the morphology of the LbL film at micrometric scale combining optical and chemical information. The morphology of the LbL film at nanometer scale was investigated by using AFM. It was observed that the films grown mechanically are thicker in relation to grown manually and present greater roughness. Also in morphological terms, the films grown mechanically have an increased number of aggregates, however, smaller in terms of average diameter, at nano and micrometric scales. It was found that the pH is a key parameter to induce the formation of molecular clusters. For instance, more homogeneous LbL films in term... (Complete abstract click electronic access below)
20
Kitagawa, Igor Lebedenco [UNESP]. "Caracterização por espectroscopia vibracional de filmes Layer-by-Layer contendo ftalocianina, polímeros condutores e gomas naturais." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/99695.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0
Previous issue date: 2009-06-19Bitstream added on 2014-06-13T19:39:43Z : No. of bitstreams: 1
kitagawa_il_me_bauru.pdf: 1240008 bytes, checksum: 9ebbdde64d8ef13b31f5e5e5f9a075cc (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Esta dissertação apresenta o estudo do crescimento (em escala nanométrica) e morfológica (em escala micrométrica) de filmes finos fabricados segundo a técnica Layer-by-Layer (LbL) contendo ftalocianina tetrasulfonada de níquel, polímeros condutores, o polímero poli(alilamina hidroclorada) (PAH), e gomas naturais. Três sistemas foram investigados: i) filmes LbL de NiTsPc e PAH; ii) filme LbL de NiTsPc, PAH e gomas naturais e iii) filmes LbL dos polímeros condutores polianilina (PANI) e poli(o-metoxianilina) (POMA) com gomas naturais. As gomas utilizadas neste trabalho foram extraídas das árvores cajueiro (Anacardium occidentale), chichá (Sterculia striata), caraia (Sterculia urens) e angico (Anadenanthera macrocarpa Benth). As caracterizações destes filmes foram realizadas por meio das técnicas de espectroscopia eletrônica utilizando absorção na região do ultravioleta-visível (UV-vis), espectroscopia vibracional por espalhamento micro-Raman e por absorção na região do infravermelho (IV) com transformada de Fourier (FTIR). Os resultados deste trabalho mostraram que, somente os filmes de NiTsPc e PAH em pH 8,5 e os filmes de NiTsPc, PAH e gomas naturais apresentaram crescimento controlado, uniformidade morfológica e química.
This dissertation presents the study of growth (in nano-scale thickness) and morphology (micrometric scale) of thin films produced using the Layer-by-Layer technique (LbL) containing nickel tetrasulfonated phthalocyanine, conducting polymers, the polymer poly(allylamine hydrochloride) (PAH), and natural gums. Three systems were investigated: i) LbL films of NiTsPc and PAH; ii) LbL films of NiTsPc, PAH and natural gums and iii) LbL films of the conducting polymers polyaniline (PANI) and poly (o-methoxyaniline) (POMA) with natural gums. The gums used in this work were obtained from the cashew (Anacardium occidentale), chicha (Sterculia striata), caraia (Sterculia urens) and angico (Anadenanthera macrocarpa Benth) trees. The characterizations of the LbL films were made using the ultraviolet-visible (UV-vis) absorption spectroscopy, vibrational spectroscopy through micro-Raman scattering and Fourier Transform infrared (FTIR) absorption. The results showed that only the LbL films of NiTsPc and PAH at pH 8.5 and the LbL films of NiTsPc, PAH and natural gums present controlled growth and morphological and chemical uniformity.
21
Peng, Chunqing. "Electrostatic layer-by-layer assembly of hybrid thin films using polyelectrolytes and inorganic nanoparticles." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43684.
Full textAbstract:
Polymer/inorganic nanoparticle hybrid thin films, primarily composed of functional inorganic nanoparticles, are of great interest to researchers because of their interesting electronic, photonic, and optical properties. In the past two decades, layer-by-layer (LbL) assembly has become one of the most powerful techniques to fabricate such hybrid thin films. This method offers an easy, inexpensive, versatile, and robust fabrication technique for multilayer formation, with precisely controllable nanostructure and tunable properties. In this thesis, various ways to control the structure of hybrid thin films, primarily composed of polyelectrolytes and indium tin oxide (ITO), are the main topics of study. ITO is one of the most widely used conductive transparent oxides (TCOs) for applications such as flat panel displays, photovoltaic cells, and functional windows. In this work, polyethyleneimine (PEI) was used to stabilize the ITO suspensions and improve the film buildup rate during the LbL assembly of poly(sodium 4-styrenesulfonate) (PSS) and ITO. The growth rate was doubled due to the stronger interaction forces between the PSS and PEI-modified ITO layer. The assembly of hybrid films was often initiated by a polyelectrolyte precursor layer, and the characteristics of the precursor layer were found to significantly affect the assembly of the hybrid thin films. The LbL assembly of ITO nanoparticles was realized on several substrates, including cellulose fibers, write-on transparencies, silicon wafers, quartz crystals, and glasses. By coating the cellulose fibers with ITO nanoparticles, a new type of conductive paper was manufactured. By LbL assembly of ITO on write-on transparencies, transparent conductive thin films with conductivity of 10⁻⁴ S/cm and transparency of over 80 % in the visible range were also prepared. As a result of this work on the mechanisms and applications of LbL grown films, the understanding of the LbL assembly of polyelectrolytes and inorganic nanoparticles was significantly extended. In addition to working with ITO nanoparticles, this thesis also demonstrated the ability to grow bicomponent [PEI/SiO₂]n thin films. It was further demonstrated that under the right pH conditions, these films can be grown exponentially (e-LbL), resulting in much thicker films, consisting of mostly the inorganic nanoparticles, in much fewer assembly steps than traditional linearly grown films (l-LbL). These results open the door to new research opportunities for achieving structured nanoparticle thin films, whose functionality depends primarily on the properties of the nanoparticles.
22
Ashcraft, James Nathan. "Tuning the transport properties of layer-by-layer thin films for fuel cell applications." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54207.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 138-148).
The increasing global focus on alternative energy sources has led to a renewed interest in fuel cells. For low power, portable applications, direct methanol fuel cells (DMFCs) are the most promising type of fuel cell. DMFCs can operate at ambient conditions and only require dilute methanol solutions and air to be input to the devices. At the core of these devices is a proton exchange membrane (PEM) that allows rapid proton transport through the polymer matrix while preventing fuel from permeating across. Additionally, PEMs must have long-term stability in the fuel cell environment, the ability to operate over a wide range of conditions (temperature and humidity), and be cost effective. A promising, robust method for fabricating polymer films with tunable properties is layer-by-layer (LbL) assembly. This technique consists of building a polymer film by sequential dipping into polymer solutions with complementary interactions, such as opposite electrostatic charges. The LbL method allows the formation of thin films that have perm-selective properties and high ionic conductivity values. This work describes the optimization of multilayer systems for use as the PEM in DMFCs. First, LbL assembled films of poly[bis(methoxyethoxyethoxy)-phosphazene] (MEEP) and poly (acrylic acid) (PAA) are demonstrated by utilizing the hydrogen bonding between these two polymers. These films show controlled thickness growth, high ionic conductivity, and excellent hydrolytic stability. The ionic conductivity of these films is optimized by tuning the assembly pH of initial polymer solutions and thereby controlling the hydrogen bonding characteristics.
(cont.) Despite similar film composition, MEEP/PAA LbL films assembled at higher pH values have enhanced water uptake and transport properties, which play a key role in increasing ion transport within the films. At fully humidified conditions, the ionic conductivity of MEEP/PAA is over one order of magnitude higher than previously studied hydrogen bonded LbL systems. The next LbL systems studied consist of a highly sulfonated aromatic polyether (sPPO) paired with amine containing polycations. The best performing sPPO system has ionic conductivity values which are the same order of magnitude as commercially relevant PEMs and has the highest ionic conductivity ever obtained from a LbL assembled film. Additionally, these LbL systems have methanol permeability values over two orders of magnitude lower than traditional PEMs. Incorporating the sPPO systems into DMFCs results in a 53% improvement in power output as compared with DMFCs using traditional PEMs. In-depth structure property studies are performed to understand the nature of the high ionic conductivity of the sPPO LbL systems with respect to film growth, composition, water uptake, and ionic crosslink density. Lastly, the mechanical properties of highly conducting LbL films are improved by forming the LbL matrix on highly tunable electrospun fiber mat (EFM) supports. Free-standing LbL films have moderate mechanical properties when dry, but are mechanically deficient when hydrated. Coating an EFM with the LbL dipping process produces composite membranes with interesting "bridged" morphologies, while still maintaining high ionic conductivity values.
(cont.) The spray LbL assembly is studied as a means for the rapid formation of LbL films on EFMs. At optimized conditions, the LbL materials conformally coat the individual fibers throughout the bulk of the EFM and have uniform surface coatings. The mechanical properties of the spray coated EMFs are shown to be superior to the pristine LbL systems.
by James Nathan Ashcraft.
Ph.D.
23
Abdelkebir, Khalil. "Développement de films "layer-by-layer" biofonctionnels : étude structurale et influence sur la biominéralisation." Rouen, 2010. http://www.theses.fr/2010ROUES019.
Full textAbstract:
Dans ce travail, nous avons utilisé la technologie LbL pour fonctionnaliser la surface des matériaux avec des films biomimétiques composés de chondroïtine sulfate (ChS), de poly-L-lysine (PLL) et d'une phosphoprotéine, la phosvitine (PhV). Ces films doivent permettre d'influencer la nucléation hétérogène et de développer des revêtements uniformes de phosphate de calcium à la surface de biomatériaux destinés au milieu osseux. Le but est d'optimiser l'ostéointégration d'implants orthopédiques et dentaires par exemple. Nos résultats s'organisent selon trois volets. Dans le premier volet, nous décrivons, au moyen d'une combinaison de techniques de caractérisation complémentaires (QCM-D, OWLS, ATR-FTIR, AFM, MEB, Microspectroscopie Raman, XPS), la structure et le mécanisme de croissance des films ChS/PLL. Dans le second volet, nous mettons en évidence l'effet destructif de la PhV sur les films ChS/PLL, et proposons un mécanisme expliquant ce comportement original. Enfin, nous étudions l'effet de la composition des dépôts décrits ci-dessus sur la cinétique de nucléation hétérogène du phosphate de calcium et la structure des dépôts obtenus. Les films comportant de la phosvitine se révélent être de meilleurs promoteurs de la nucléation hétérogène que les films terminés par une couche de ChS ou de PLL. Au-delà d'un certain degré de sursaturation, la phosvitine s'organise en agrégats, ce qui a pour effet de niveler l'influence de la sursaturation sur la cinétique de nucléation hétérogène. On obtient des dépôts de phosphate de calcium uniformes composés de phosphate octocalcique (un précurseur biologique de l'hydroxyapatite) et d'hydroxyapatite. Ce résultat est pertinent et prometteur en vue des applications recherchéesIn this study, LbL technique is explored as a potential method for surface functionalization of biomaterials. A typical goal of this work is to control the heterogeneous nucleation of calcium phosphate (CaP) at surfaces in order to optimize the osseointegration process of dental and orthopaedic implants. The LbL films studied are comprised of the biomimetic polyelectrolytes chondroitin sulfate (ChS) and poly-L-lysine (PLL) and of the phosphorylated protein phosvitin (PhV). We first describe the structure and buildup mechanism of the ChS/PLL films by means of complementary techniques (QCM-D, OWLS, ATR-FTIR, AFM, MEB, Raman confocal microspectroscopy, XPS). Then, we describe original destructive interactions between PhV and the ChS/PLL film, and we suggest a mechanism explaining this behaviour. Finally, we investigate the influence of the films on the heterogeneous nucleation kinetics and on the structure of CaP obtained from supersaturated solutions. We establish that PhV as the outer layer was a better promoter of CaP nucleation than ChS or PLL, as it lowers both the critical calcium phosphate supersaturation required for heterogeneous nucleation and the induction time. Beyond a certain degree of supersaturation, phosvitin self-assembles into clusters, which levels the impact of supersaturation on the heterogeneous nucleation kinetics. We obtain dense, thick and uniform CaP coatings comprised of octacalcium phosphate (a precursor of biological hydroxyapatite), which constitutes a promising result with regards to the applications considered
24
Cho, Szu-Hao. "FACILE AND FAST FABRICATION OF FUNCTIONAL THIN FILMS VIA POLYELECTROLYTE LAYER-BY-LAYER ASSEMBLY." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1597419056509933.
Full text
25
Choi, Kyungsun. "Multilayer thin films by layer-by-layer (LBL) assembly of functional polyelectrolytes their optical and electrochemical properties /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982377584.
Full text
26
Furini, Leonardo Negri. "Carbendazim e modelos de biomembrana via filmes de Langmuir e Layer-by-Layer : mecanismos de interação e desenvolvimento de sensores /." Bauru, 2016. http://hdl.handle.net/11449/136450.
Full textAbstract:
Orientador: Carlos José Leopoldo ConstantinoCoorientador: Gustavo Fernandes Souza Andrade
Banca: Paola Corio
Banca: Clarissa de Almeida Olivati
Banca: Sérgio Antonio Marques de Lima
Resumo: Nesta tese filmes de Langmuir foram empregados para estudar a interação entre lipídios e um fungincida denominado carbendazim (MBC) e espectroscopia de impedância e espalhamento amplificado em superfície (SERS, do inglês, surface-enhanced Raman scattering) empregados na detecção deste fungicida. Os lipídios utilizados para formar os filmes de Langmuir forma brometo de dioctadecildimetilamônio (DODAB), brometo de didodecilmetilamônio (DDAB), 1,2-diplamitoil-sn-3-glicero-fosfatidilcolina (DPPC) e 1,2-dipalmitoil-sn-3-glicero-[fosfo-rac-(1-glicerol)] (DPPG) e o estudo da interação foi realizado com e sem MBC na subfase aquosa. Os resultados mostraram que o MBC interage fortemente com o DODAB e DDAB, moderadamente com o DPPC e fracamente com o DPPG, indicando que a interação é de origem eletrostática. Unidades sensoriais compostas por eletrodos interdigitalizados recobertos com filmes LbL de DODAB/NiTsPc e perileno/DPPG compuseram uma língua eletrônica capaz de distinguir diferentes concentrações de MBC em solução via espectroscopia de impedância. Analisamos individualmente cada unidade sensorial, a composta pelo filme LbL de DODAB/NiTsPc foi a que apresentou melhor desempenho frente ao MBC. Os estudos SERS foram realizados em três etapas. Na primeira, várias morfologias de nanopartículas foram sintetizadas e avaliadas quais apresentam melhor sinal SERS do MBC. Deste estudo ficou determinado que as nanopartículas esféricas de prata apresentaram o melhor sinal SERS do MBC. A interação do MBC com a superfície destas nanopartículas foi realizada a partir de espectros SERS do MBC em vários pHs. Cálculos teóricos foram utilizados para atribuição dos modos vibracionais do MBC e assim na interpretação dos resultados experimentais. De principal relevância, das espécies de MBC as formas neutra (MBC0) e desprotocolada (MBC) apresentam afinidade pela superfície de prata, originando assim sinal SERS. Por fim, o limite...
Abstract: This work Langmuir films were employed to study the interactions between lipids and a fungicide called carbendazin (MBC), impedance spectroscopy and surface-enhanced Raman scaterring (SERS) were used in the detection of this fungincide. The lipids employed to Langmuir films were dioctadecyldimethylammonium bromide (DODAB), didodecyldimethylammonium bromide (DDAB), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) with and without MBC in the subphase. The results show that the MBC interacts strongly with DODAB, moderately with DPPC and weakly to DPPG, indicating that it is electrostatic interaction. Sensor units composed of interdigitated electrodes coated with LbL films DODAB/NiTsPc and perilene/DPPG composed and electronic tonque able to distinguish different MBC concentrations in solution, via impedance spectroscopy. Analyzing each sensory unit, the composed with LbL film DODAB/NiTsPc showed the best performance. The SERS studies were performed in three stages. The first one, several morphologies of nanoparticles were synthesized and evaluated which lave better SERS signal of MBC. From this study it was concluded that the sherical nanoparticles of silver have better SERS signal of MBC and the subsequent results were obtained only with this nanoparticle. The interaction between MBC and surface of these nanoparticles was carried out by SERS spectra of MBC at several pHs. Here, theoretical calculations were used for assignment of vibrational modes of the MBC and thus help in the interpretation of experimental results. According to experimental and theoretical results neutrally (MBC0) and deprotonated (MBC) species have affinity for the silver surface and then show SERS signal. Finally, the MBC limit of detection was determined via SERS using a procedure which ensures that the reproducibility of the measurements, since SERS technique is not, yet, a routine analytical technique
Doutor
27
Taketa, Thiago Bezerra 1988. "Obtenção e caracterização de recobrimentos de quitosana/ácido hialurônico e quitosana/alginato de sódio pela técnica layer-by-layer para aplicações antimicóticas." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266611.
Full textAbstract:
Orientador: Marisa Masumi BeppuDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-22T20:50:50Z (GMT). No. of bitstreams: 1 Taketa_ThiagoBezerra_M.pdf: 4178929 bytes, checksum: 10d5bd8df33f074970da2596a3ef43a0 (MD5) Previous issue date: 2013
Resumo: A busca por materiais que possam constituir superfícies antimicrobianas é relevante uma vez que o contato com micro-organismos patogênicos representa um sério risco à saúde. Além das propriedades naturais biocidas de alguns materiais, a adição de compostos que também atuam como agentes antibióticos como íons metálicos ou peptídeos, podem potencializar essa funcionalidade. Existe também a alternativa de criar-se uma superfície antimicrobiana através da modificação da densidade e da mobilidade de cargas catiônicas dos materiais utilizados, assim como propriedades estruturais dos revestimentos visando dificultar a adesão ou crescimento de micro-organismos. Neste trabalho, os filmes foram construídos pela técnica layer-by-layer, na qual é feita a imersão de um substrato (lâmina de vidro) alternadamente em soluções que contêm cargas positivas ou negativas e, no intervalo entre cada submersão, o filme em formação passa por um processo de lavagem em água deionizada para a retirada do excesso de polieletrólitos. Especificamente, foram utilizados o biopolímero catiônico quitosana (CHI) e os polieletrólitos negativos alginato de sódio (ALG) e ácido hialurônico (HA). Os filmes constituídos de ALG/CHI e HA/CHI foram construídos em diferentes pH e força iônica das soluções polieletrolíticas. Por análises de perfilometria e microscopia de força atômica (AFM) foi possível monitorar mudanças de espessura e rugosidade dos recobrimentos e foi verificado que a presença de sal no meio de deposição faz com que os polímeros apresentem conformações com mais loops e tails e esse arranjo das cadeias em solução é transmitido para os filmes, que se tornam mais rugosos. Além disso, a espessura dos filmes pode ser controlada por meio do ajuste do pH do meio de deposição. A incorporação dos corantes rosa de bengala e azul de alciano, em conjunto com análises de FTIR possibilitou identificar os grupos funcionais responsáveis pela funcionalidade dos recobrimentos formados. Por fim, foram feitos testes dos recobrimentos, com e sem acetato de prata, frente à cepa Candida albicans e foi verificado que filmes contendo Ag+ foram capazes de inibir o crescimento do fungo. O uso sinérgico de polímeros naturais e da técnica LbL viabilizou, de uma maneira simples e versátil, a construção de filmes nanoestruturados com potencial para aplicações antimicóticas
Abstract: The search for materials that can constitute antimicrobial surfaces is relevant since the contact with pathogenic microorganisms is a serious health risk. Besides the natural biocidal properties of some materials, the addition of compounds that also act as antimicrobial agents, such as metal ions or peptides, may enhance this capability. There is also the alternative to create an antimicrobial surface by modifying the density and mobility of cationic charges of the materials used, as well as structural properties of the coatings in order to hinder the adhesion or proliferation of microorganisms. In this work, the nanostructured films were built by the layer-by-layer (LbL) technique, whose interaction among species with opposite electrostatic charges is, in most cases, the primary phenomenon responsible for the formation of multilayers. Specifically, we chose the cationic biopolymer chitosan (CHI) and the negative polyelectrolytes sodium alginate (ALG) and hyaluronic acid (HA). The aim of this study was to evaluate the effect of ionic strength (0 versus 200 mM) and pH (3 versus 5) on ALG/CHI and HA/CHI nanostructured multilayered thin films properties. From profilometry and atomic force microscopy (AFM) analysis, it was possible to monitor changes in thickness and roughness of the coatings and it was found that the presence of salt in polyelectrolyte solutions promoted polymer chains conformations with more loops and tails and this arrangement in solution is transmitted to films, resulting in rougher coatings. Furthermore, the film thickness can be precisely controlled by adjusting the pH of the polyelectrolyte solution. The incorporation of rose bengal and alcian blue dyes in conjunction with FTIR analysis allowed identifying the functional groups responsible for the functionality of the coatings formed. Finally, we evaluated the antifungal activity of the LbL coatings (with and without silver ions) against Candida albicans strain and we observed that films containing Ag+ were able to inhibit the growth of the fungus. The synergistic use of natural polymers and LbL technique made possible, in a simple and versatile way, the construction of nanostructured films with great potential for antifungal surfaces
Mestrado
Engenharia de Processos
Mestre em Engenharia Química
28
Geraldo, Vananélia Pereira Nunes. "Filmes nanoestruturados contendo lipossomos para liberação controlada do Ibuprofeno." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-17062008-120210/.
Full textAbstract:
A liberação controlada de fármacos é um tópico importante para várias iniciativas em nanotecnologia devido ao possível impacto para a sociedade, com a criação de sistemas otimizados que garantam a liberação num sítio específico e a uma taxa controlada. Dentre os vários paradigmas de liberação controlada destaca-se o uso de lipossomos, uma vez que muitos fármacos e drogas podem ser transportados. Este trabalho descreve a fabricação de filmes automontados de lipossomos que incorporam o fármaco ibuprofeno. Os lipossomos foram preparados de dipalmitoil fosfatidil colina (DPPC), dipalmitoil fosfatidil glicerol (DPPG) e palmitoil-oleoil fosfatidil glicerol (POPG), cujas camadas foram alternadas por interações eletrostáticas com camadas do dendrímero PAMAM geração 4. Medidas de espalhamento dinâmico de luz indicaram que a incorporação do ibuprofeno tornou os lipossomos de DPPC e DPPG mais estáveis, com uma diminuição no diâmetro médio de 140 para 74 nm e 132 para 63nm, respectivamente. Ao contrário, os lipossomos de POPG ficaram menos estáveis, com aumento do diâmetro de 110 para 160 nm. A influência na estabilidade foi confirmada em medidas de microscopia de força atômica nos filmes automontados, que mostraram grande tendência à ruptura nos lipossomos de POPG com a incorporação de ibuprofeno. O crescimento dos filmes automontados foi investigado com espectroscopia de fluorescência e uma balança de cristal de quartzo. A intensidade da fluorescência devida ao ibuprofeno aumentou exponencialmente com o número de camadas depositadas, mas não por causa de uma crescente adsorção de ibuprofeno. Ao contrário, a quantidade de material adsorvido nas primeiras camadas aumentou inicialmente, mas depois diminuiu drasticamente após a 6ª. bicamada, e o filme praticamente pára de crescer a partir da 10ª. bicamada. Portanto, a grande fluorescência para filmes espessos deve ser associada a um ambiente favorável, que aumenta a emissão quântica do ibuprofeno. A liberação do ibuprofeno, estudada com medidas de fluorescência, é mais lenta quando incorporado em lipossomos. Em experimentos com uma membrana de diálise, notamos que o tempo de decaimento do ibuprofeno puro é 5,2 h, enquanto este tempo aumentou para 9,2 e 8 h para ibuprofeno encapsulado em lipossomos de DPPG e POPG, respectivamente. O ibuprofeno também foi liberado de filmes automontados contendo lipossomos de DPPG e POPG, o que é promissor para o uso em bandagens (patches).Controlled drug delivery is a key issue in a number of nanotechnology endeavors owing to the large impact on society that may achieved if improved systems are created which allows for delivery at a specific target and with a controlled rate. Among the various paradigms employed in drug delivery, the use of liposomes is prominent because a variety of drug molecules can be carried. This work describes the fabrication of layer-by-layer (LbL) films made with liposomes incorporating ibuprofen. The liposomes were made with dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl glycerol (DPPG) and palmitoyl-oleoyl-phosphatidyl glycerol (POPG), whose layers were alternated with layers of the dendrimer PAMAM generation 4 via electrostatic interactions. According to dynamic light scattering measurements, the incorporation of ibuprofen caused DPPC and DPPG liposomes to become more stable, with a decrease in diameter from 140 to 74 nm and from 132 to 63 nm, respectively. In contrast, liposomes from POPG became less stable, with an increase in size from 110 to 160 nm. These results were confirmed with atomic force microscopy images of LbL films, which showed a large tendency to rupture for POPG liposomes. The film growth was monitored with fluorescence spectroscopy and a quartz crystal microbalance (QCM). The fluorescence intensity arising from ibuprofen increased exponentially with the number of layers, but this was not caused by an increased adsorption of ibuprofen. Instead, the QCM measurements showed that the amount of material adsorbed increases initially with the number of PAMAM/liposome(ibuprofen) layers, but after the 6th bilayer it decreases sharply and film growth practically stops after the 10th layer. Therefore, the inevitable conclusion is that the increased fluorescence is due to a favorable environment for the ibuprofen, whose quantum emission efficiency increases with the number of layers deposited. Also using fluorescence measurements, we noted that release of ibuprofen was delayed when incorporated in liposomes. For instance, in a membrane dialysis experiment, the characteristic decay time was 3.5 h for ibuprofen in solution, whereas this time increased to 9.2 and 8 h for ibuprofen encapsulated into DPPG and POPG liposomes, respectively. Ibuprofen could also be released from the LbL films made with DPPG and POPG liposomes, which is promising for further use in patches.
29
Mauroy, Cyprien. "Films multicouches nanocristaux de cellulose/Ge-Imogolite pour l'élaboration de nouveaux matériaux nanoporeux." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0265/document.
Full textAbstract:
Lors des dix dernières années, les films multicouches ont suscité l’intérêt de la communauté scientifique pour leurs propriétés innovantes. Principalement issus de l’association de polyélectrolytes et/ou de nanoparticules de différentes morphologies, ils ont ouvert la voie à la fabrication d’une nouvelle catégorie de matériaux nanoporeux, possédant des propriétés optiques attractives telles que la coloration structurale et l’antireflet. Les films multicouches à base de deux nanoparticules de charges opposées sont plus rares et permettent de jumeler les propriétés des deux nanoparticules utilisées et d’en faire émerger de nouvelles. Dans cette étude, nous nous sommes intéressés à deux nanoparticules anisotropes, de facteurs d’aspects contrôlés et respectivement bio/geosourcées : les nanocristaux de cellulose (NCC) et des nanotubes d’imogolite. Le but de cette étude est d’étudier la possibilité de créer un film multicouche bio-géo inspiré à base de ces deux nanoparticules par immersion et d’en étudier les propriétés optiques. Dans un premier temps, nous avons comparé les films multicouches NCC/Ge-imogolites à ceux plus communément décrits dans la littérature, à savoir, des films à base de NCC ou d’imogolite associés à un polyélectrolyte de charge opposée. Les différents paramètres de trempage comme le temps d’immersion et la force ionique de la suspension ont été variés afin d’obtenir une densité de film optimale. Pour finir la porosité des films et leur comportement dans l’eau ont été étudiés par QCM-D, ainsi que leurs propriétés optiques par mesure de transmittanceIn the past decade, multilayer thin films drew the scientific community attention for their unique properties. Indeed, principally made of an association of polyelectrolytes and/or nanoparticles, of various morphologies and chemistries, they allow the design of a range of porous nanomaterials with unique optical properties, such as structural colors or anti-reflectivity. Less commonly described, thin films made of two nanoparticles of opposite charges are gaining interest since they combine the properties of the two nanoparticles used, and generate new ones through their association. In this study, multilayer coatings were formed through the association of two anisotropic oppositely charged nanorods of well-controlled aspect ratio, i.e. bio-based anionic cellulose nanocrystals (CNC) and geo-based cationic Imogolites. This study deals with the feasibility to create a bio-geo-inspired multilayer thin film based on these two nanoparticles by dipping and characterize their optical properties. Firstly, elaboration of multilayered thin films from CNC and Ge-Imogolites nanorods, were studied in comparison with reference films incorporating CNC or Imogolites with polyelectrolytes bearing opposite charges of the nanorods. Multilayered thin films were assembled by the dipping procedure and various parameters (adsorption time, ionic strength, etc.) were varied to investigate the optimal density for the film. To finish, film porosities were investigated using QCM-D, and optical properties were investigated by transmittance measurements
30
McNeill, David William. "Semiconductor layer growth by rapid themal chemical vapour deposition." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238986.
Full text
31
Vasconcellos, Fernando da Cruz. "Produção de nanoestruturas de biopolímeros através de deposição "Layer-by-Layer" com propriedades antibacterianas e de imobilização de linfócitos." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266901.
Full textAbstract:
Orientador: Marisa Masumi BeppuTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-18T11:40:54Z (GMT). No. of bitstreams: 1 Vasconcellos_FernandodaCruz_D.pdf: 16906370 bytes, checksum: f307344fa0f9ccb976c0dbb73c5bf226 (MD5) Previous issue date: 2011
Resumo: O trabalho trata da produção de filmes nanoestruturados multicamadas de biopolímeros sobre substratos sólidos com a técnica de deposição layer-by-layer (LbL). A técnica de montagem layer-by-layer é uma ferramenta adequada para produção controlada de filmes de multicamadas com propriedades importantes tais como: a biocompatibilidade, a biodegrabilidade, a baixa toxicidade, a hidrofilicidade e a baixa citotoxicidade, concedendo a estes filmes grande versalitidade em suas aplicações. O foco principal da pesquisa foi estudar multicamadas dos polieletrólitos naturais quitosana e ácido hialurônico e sua aplicabilidade para: 1) promover a adesão de linfócitos B, 2) gerar superfícies antibacterianas. Os testes da preparação e o estudo da variação de parâmetros de montagem de filmes dos biopolímeros, assim como sua caracterização foram úteis para a avaliação dessas aplicações. O estudo também incluiu a produção de filmes multicamadas contendo outros biopolímeros (alginato de sódio e carboximetilcelulose), assim como polímeros sintéticos e nanopartículas. A caracterização dos filmes envolveu diversas técnicas de análise, dentre elas: microscopia de força atômica (MFA), que permitiu obter informações sobre a topologia e elasticidade dos filmes, e microbalança de cristal de quartzo com dissipação (QCM-D), que permitiu fazer uma análise em tempo real das características dos filmes durante a deposição dos biopolímeros. Os resultados obtidos neste trabalho mostram a viabilidade da fabricação de filmes multicamadas a base de biopolímeros para uso na imobilização de linfócitos B. Os resultados mapeiam e otimizam as variáveis de preparação dos filmes de multicamadas dos polieletrólitos (PEMs) de HA e CHI através do pH, força iônica, e última camada depositada, que influenciam a imobilização seletiva dos linfócitos. Estes filmes exploram as interações CD44-ácido hialurônico sem a necessidade de utilização de reações químicas agressivas e promovem a adesão seletiva de linfócitos assegurando a viabilidade, habilidade de replicação e funções dos linfócitos, após a imobilização. Filmes assim construídos tem aplicação em biossensores a base de células, engenharia do sistema imune, sistemas de diagnóstico e tratamento de doenças entre outras. Os resultados mostraram também que a técnica LbL é viável para a construção de superfícies antibacterianas. As propriedades antibacterianas e de imobilização de linfócitos da superfície desses filmes são passíveis de aplicações biotecnológicas
Abstract: This thesis is on the production of biopolymer nanostructured multilayered thin films deposited on solid substrates utilizing the layer-by-layer (LbL) deposition technique. The layer-by- layer deposition technique of assembly is a simple yet versatile and powerful tool for the controlled production of biopolymer multilayered thin films carrying important properties, such as: biocompatibility, biodegradability, low toxicity, hydrophilicity, low cytotoxicity, which entice them as candidates for a wide variety of applications. The main focus of the research was the study of natural biopolymer polyelectrolytes such as chitosan and hyaluronic acid, and their applicability in: 1) promoting the adhesion of B lymphocytes, and 2) generating antibacterial surfaces. The film preparation process in itself and the study of the film properties as a function of deposition parameters, such as pH and ionic strength, during assembly, were very important in tailoring the multilayer film for specific applications. The study also included the production of multilayered films composed by other biopolymers (sodium alginate, carboxymethylcellulose), as well as by synthetic polymers and nanoparticles. The characterization of the films involved various techniques, such as: atomic force microscopy (AFM) - which allowed the acquisition of information regarding film topology and elasticity, and the quartz crystal microbalance with dissipation (QCM-D), which permitted an analysis, in real time, of the film characteristics during deposition of the biopolymers. The results obtained in this work show the feasibility of fabricating multilayered thin films based on biopolymers for their use in the adhesion of B lymphocytes. The results map out and optimize the preparation of polyelectrolyte multilayered (PEMs) composed of HA and CHI through the variation of pH, ionic strength, and choice of last layer deposited, all factors that influence the selective immobilization of lymphocytes. These films explore the CD44- hyaluronic acid interactions without the use of aggressive chemical reactions to promote the selective adhesion of lymphocytes, maintaining their viability, meaning, maintaining their ability to replicate and their native functions after being immobilized. The results also show the feasibility of the LbL technique in producing biopolymer films having antibacterial properties. Both film characteristics - the adhesion and the antibacterial properties - find applicability in the area of bionanotechnology. These films may be used in the fabrication of cell based sensors, in immune system engineering, in diagnostics systems and in disease treatments, among others
Doutorado
Engenharia de Processos
Doutor em Engenharia Química
32
Palumbo, Marco. "Layer-by-layer assembly of organic films and their application to multichannel surface plasmon resonance sensing." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3094/.
Full textAbstract:
This thesis provides a study of a single chip, multi-channel surface plasmon resonance (SPR) imaging system. The equipment has no moving parts and uses a single sensor "chip" onto which multiple channels can be incorporated. A light emitting diode is used as a photon source while a CCD camera forms the detector. The optical configuration has been designed to achieve a uniform illumination of the sample over a fixed area with a range of incident angles. Poly(ethylene imine), PEI, poly(ethylene-co-maleic acid), PMAE, poly(styrene sulfonate), PSS, and a cationic modified polyacrylic ester, PMADAMBQ, are used as the molecular "bricks" in layer-by-layer (LbL) self-assembled organic architectures. Reflectivity changes in real time are used to follow the adsorption steps during the deposition of the multilayer films. Sensing experiments are mainly focused on the first row transition metals such as iron (II), nickel (II), copper (II)and zinc (II). Sensing of anionic sodium dodecylbenzene sulphate, C(_12)H(_25)C(_6)H(_4)SO(_3)Na, and a reversible pH-dependent response for a PEI/PMAE/PMADAMBQ LbL film are also reported. Using a two bilayer structure, PEI/PMAE/PMADAMBQ/PMAE, a detection limit of less of one part per million for copper ions in solution is measured. Atomic force microscopy is used to elucidate the morphology of the organic films. In some cases, the visualization of isolated polymeric chains is demonstrated. It is proved that polyelectrolytes of different charge density form dissimilar structures. The outer surface of PEI/PSS bilayers appears to be more uniform than that of PEI/PMAE bilayers. This is believed to have an influence on the sensing performance of the LbL architectures. The use of the SPR sensing system for simultaneous interrogation of different polyelectrolyte thin films is demonstrated. Two different LbL self-assembled films, PEI/PSS and PEI/PMAE, are built-up on the same chip. Their response to a variety of metal ions is shown to be independent and reasonably reproducible. Moreover, consistent results are obtained when using sensing chips stored for a relatively long time.
33
Shimazaki, Yuzuru. "Studies on the Layer-by-Layer Deposited Ultrathin Polymer Films Based on the Charge-Transfer Interaction." Kyoto University, 2001. http://hdl.handle.net/2433/150662.
Full text
34
Storti, Felipe Chagas. "Estudo da arquitetura molecular de filmes layer-by-layer de ftalocianina tetrasulfonada de cobre /." Presidente Prudente, 2008. http://hdl.handle.net/11449/88497.
Full textAbstract:
Orientador: Carlos José Leopoldo ConstantinoBanca: Marystela Ferreira
Banca: Luciana Gaffo
O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: Nesta dissertação é apresentado um estudo envolvendo a arquitetura molecular (crescimento controlado, morfologia e organização molecular) de filmes Layer-by-Layer (LbL) contendo ftalocianina tetrasulfonada de cobre (CuTsPc). Inicialmente foram realizados estudos sobre a cinética de crescimento desses filmes para determinação do tempo de adsorção do material no substrato. Uma vez determinado este tempo, filme LbL foram fabricados utilizando soluções catiônica de poli(alilamina) hidroclorada - PAH) e aniônica de CuTsPc. Os filmes de PAH/CuTsPc foram produzidos de forma manual e utilizando um braço mecânico em valores de pHs 2,5; 5,5 e 8,5 sendo então caracterizados por espectroscopia eletrônica via absorção na região do ultravioleta-visível (UV-Vis), espectroscopia vibracional via espalhamento Raman e absorção na região do infravermelho com transformadora de Fourier (FTIR) e microscopias óptica e força atômica (AF,A). A espectroscopia de absorção na região do UV-Vis foi utilizada para acompanhar o crescimento do filme LbL assim como investigar a presença de agregados. A técnica de FTIR permitiu investigar as interações entre o PAH e a CuTsPc e determinar a organização molecular comparando filme LbL e cast. O acoplamento entre microscópio óptico e espectrógrafo Raman (técnica microRaman) possibilitou analisar a morfologia do filme LbL em escala micrométrica combinando informações ópticas e químicas. A morfologia do filme LbL em escala nanométrica foi investigada utilizando-se AFM. Foi observado que os filmes crescidos mecanicamente são mais espessos em relação aos crescidos manualmente, além de apresentarem maior rugosidade. Ainda em termos morfológicos, os filmes crescidos mecanicamente apresentam uma maior quantidade de agregados, porém, menores em termos de "diâmetro médio", tanto em escala nano como micrométrica... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This dissertation presents a study involving the molecular architecture (controlled growth, morphology, and molecular organization) of layer-by-layer (LbL) films containing copper phthalocyanine tetrasulfonated (CuTsPc). Initially, the studies were performed on the kinetics of growth of these films to determine the time of adsorption of the material on the substrate. Once determined this time, LbL films were produced by using solutions of cationic poly (hydrochloric alilamina - PAH) and anionic CuTsPc. The films of PAH / CuTsPc were produced either manually or using a mechanical arm in pH values of 2.5, 5.5, and 8.5, and then characterized by electron spectroscopy via absorption in the ultraviolet-visible (UV-Vis), vibrational spectroscopy by Raman scattering and absorption in the infrared region with Fourier transform infrared (FTIR) and optical microscopy and atomic force microscopy (AFM). The absorption spectroscopy in the UV-Vis was used to follow the growth of the LbL film and to investigate the presence of aggregates. The FTIR technique allowed investigatin the interactions between the PAH and CuTsPc and determining the molecular organization comparing LbL films and cast. The coupling between optical microscope and Raman spectrograph (micro-Raman technique) allowed analyzing the morphology of the LbL film at micrometric scale combining optical and chemical information. The morphology of the LbL film at nanometer scale was investigated by using AFM. It was observed that the films grown mechanically are thicker in relation to grown manually and present greater roughness. Also in morphological terms, the films grown mechanically have an increased number of aggregates, however, smaller in terms of "average diameter", at nano and micrometric scales. It was found that the pH is a key parameter to induce the formation of molecular clusters. For instance, more homogeneous LbL films in term... (Complete abstract click electronic access below)
Mestre
35
Hewson, Daniel James. "Iridescence and circular dichroism in cellulose nanocrystal thin films." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/32480.
Full textAbstract:
Only in recent times has the true potential of cellulose as a high-end functional and sustainable material been realised. As the world’s most abundant resource cellulose has been utilised by man throughout history for timber, paper and yarns. It is found in every plant as a hierarchical material and can be extracted and converted into fibres which are of great use, especially in the form of nanofibrous materials. This thesis has focused on the utilisation and ability of cellulose nanocrystals (CNCs) to generate structural colour in fabricated thin films. This has been achieved in two ways: Firstly, the natural morphology of CNCs and their ability to form a suspension have been applied to a layer-by-layer (LbL) regime to produce tunable Bragg reflecting thin films. Secondly, a novel technique combining profilometry and spectroscopy has been developed to estimate the distribution of CNCs within EISA thin films and correlate this with the optical properties of the film. This thesis reports the successful fabrication of synthetic CNC LbL Bragg reflecting thin films. The film was compiled using an additive layer-by-layer technique which allowed the construction of a multi-layered thin film and control over individual layer thicknesses and refractive index. Also reported is the discovered reflection of both left and right handed circularly polarised light (CPL) from CNC EISA thin films. These reflections were found to correlate with CNC distribution within the thin films. The distribution of CNCs was estimated using a novel technique which combined spectroscopically measured film absorbance as a function of the volume of the film area under investigation. The specific volumes were calculated using profilometry measurements and the beam spot size used in the spectroscopy measurements.
36
Li, Yihong. "Bio-enabled syntheses of functional mineral oxide thin films." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52955.
Full textAbstract:
The bio-enabled syntheses of functional nano-structured metal oxide thin films is of importance for a range of applications, in photonics, electronics, sensing, cell engineering, and biochemical devices. This type of novel syntheses method can overcome problems common in conventional oxide processing. In general, conventional oxide processes often require thermal treatment, caustic chemicals, and mechanical processing when producing shape-controlled inorganic materials. In contrast, biological processes are usually carried out under mild conditions (low temperature, neutral pH, and atmospheric pressure) and are therefore promising for the development of benign processes. Functional materials synthesized at room temperature using biomolecules are promising due to their expediency. During recent years, significant discoveries and progress have been made in discovering, and finding new applications for such biomimetic oxide-based minerals. However, much of the research has focused on SiO- and TiO-bearing organic-inorganic hybrid materials, of which a significant limitation is that, there are relatively few water-soluble inorganic oxide precursors commercially available for such biological syntheses. Two common compounds that are used in the biomimetic syntheses of SiO₂ and TiO₂ are tetramethoxisilane (TMOS) and Ti(IV) -bis(ammonium lactato) dihydroxide ( TiBALDH ). As a result, approaches to synthesize new water-soluble transitional metal complexes for use as precursors in the biomineralization of the corresponding functional metal oxide thin films were explored in this work, in order to expand the range of functional oxide chemistries formed via bio-enabled methods. A Ti-containing compound was synthesized to compare the behavior of commercially-available and as-synthesized TiBALDH. Another titanium-containing complex with citrate ligands, instead of lactate, was also synthesized to investigate the influence of the ligand type on the deposition behavior of the precursors. Zirconium- and hafnium-containing complexes were also synthesized to demonstrate the feasibility and versatility of the idea of applying bio-enabled syntheses to the fabrication of functional mineral oxides other than the reported SiO₂ and TiO₂. The second part of this thesis focuses on developing a novel way to fabricate porous functional mineral oxide thin films with controlled pore size, which can be used in a variety of applications, such as dye loading for optical, photochemical, or electrochemical purposes. Commercially-available, carboxyl-group-terminated polystyrene spheres of different sizes were utilized as pore-size controllers in the bio-enabled syntheses of TiO₂ by protamine. This approach has been found to be an effective means of creating uniform pores in inorganic mineral oxide coatings. The accomplishments of this work have the potential to be integrated so as to expand the boundaries of biomineralization in materials science and engineering fields.
37
Spears, Mark William. "Microgel-based coatings and their use as self-healing, dynamic substrates for bioapplications." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53060.
Full textAbstract:
Microgels are solvent swollen, cross-linked polymer macromolecules of micro or nanoscale dimensions. In this work, microgels are used as versatile building blocks in layer-by-layer assemblies to form thin coatings. While conceptually simple materials, these microgel-based films actually possess extremely complex behavior as evidenced by two particular areas. First, microgel films have self-healing properties, allowing them to rapidly recover from damage in the presence of solvent. The healing step requires rearrangement of film components, demonstrating the dynamic and mobile nature of the films. Second, fibroblasts display complex behavior on microgel films arising from the properties of the coating. A chemical crosslinking treatment of the film affects the film network structure in a concentration-dependent manner. These network changes result in altered mechanical properties that are the primary controlling factor in determining cell behavior at the interface. These data suggest that fibroblasts are not solely controlled by the film elasticity, but rather by the viscoelasticity, and there is a viscoelastic range that results in maximal cell spreading.
38
Garg, Akhilesh. "Organic Self-Assembled Films for Nonlinear Optics: Film Structure, Composition and Kinetics of Film Formation." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28872.
Full textAbstract:
Organic materials exhibiting second-order non-linear optical (NLO) properties are a key to the development of advanced electro-optic (EO) modulators used in fiber-optic communications system. This work addresses the fabrication and characterization of organic materials with NLO properties using a self-assembly approach by alternately dipping a charged substrate into positively and negatively charged polymers to build up layer-by-layer (LbL) films.
The effect of solution pH on the formation of LbL films fabricated using the polycation poly(allylamine hydrochloride) (PAH) and the polyanion poly{1-[p-(3–-carboxy-4–-hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl} (PCBS) was studied using a quartz crystal microbalance with dissipation (QCM-D) monitoring, ellipsometry, absorbance, and second harmonic generation (SHG) measurements. PCBS has an azo-benzene chromophore side group that, when sufficiently oriented, results in measurable SHG. Films of PAH/PCBS fabricated at neutral pH where both PAH and PCBS are highly charged led to thin bilayers, ~1 nm, with a 1:1 molar ratio of PCBS:PAH. This molar ratio was found to be important for long-range polar ordering of PCBS in these films. Increasing the rate of convection was found to reduce the time required for complete adsorption of the polyion. This can have a significant impact on fabrication of films with high bilayer numbers.
A variation of the above technique, which involves adsorbing one of the constituents electrostatically and another covalently, was studied using PAH and a reactive dye, Procion Brown (PB), which has a significantly higher hyperpolarizability than PCBS. It was found that a high pH, ~10.5, was important for achieving covalent attachment of the PB to the underlying PAH films. This resulted in much higher SHG intensities compared to when PB was deposited pH at 8.5-9.5 where the attachment of PB was due to a combination of electrostatic and covalent interactions. QCM-D results for PAH/PB films revealed the presence of a high percentage of unreacted amine groups in the underlying PAH film. A rate constant value for PB attachment step to the underlying PAH was also calculated.
To enhance the SHG intensity of these films, silver nanoprisms were synthesized and deposited onto films using physisorption. An enhancement in the SHG intensity was observed for both PAH/PCBS and PAH/PB films.Ph. D.
39
Osypova, Alina. "Design of multi-stimuli responsive films through layer-by-layer assembly for the control of protein adsorption." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066727.
Full textAbstract:
L'adsorption de protéine sur une surface artificielle solide est un phénomène fondamental qui détermine la réponse biologique d'un organisme vivant entrant dans n'importe quel matériel d'implant. Donc, l'adaptation de surfaces pour l'adsorption de protéine contrôlée est au coeur de beaucoup de champs de recherche d'aujourd'hui incluant la science de matériels et la biotechnologie. Dans ce contexte, les matériels sensibles de stimulus qui peuvent changer leurs propriétés comme une réponse à une petite monnaie dans leur environnement physicochimique attirent un grand intérêt comme ils permettent la création de surfaces avec des propriétés commutables pour le contrôle d'adsorption de protéine. Dans cette thèse, nous faisons un rapport sur la conception et l'élaboration de films minces sensibles de stimulus multi et de nanotubes. À cette fin, nous avons employé la couche-par-couche robuste et polyvalente…Protein adsorption on a solid artificial surface is a fundamental phenomenon that determines the biological response of a living organism entering any implant material. Therefore, tailoring surfaces for controlled protein adsorption is at the heart of many of today's research fields including biotechnology and materials science. In this context, stimuli-responsive materials that are able to change their properties as a response to a small change in their physico-chemical environment are attracting a great interest as they allow the creation of surfaces with switchable properties for the control of protein adsorption. In this thesis, we report on the design and elaboration of multi stimuli-responsive thin films and nanotubes. For this purpose, we employed the robust and versatile layer-by-layer (LbL) assembly technique to incorporate block copolymers made of poly(acrylic acid) PAA and poly(N-isopropylacrylamide) PNIPAM with tunable and well-controlled block lengths. The combination of ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and infrared data reveal the possibility to build up (PAH/PAA-b-PNIPAM)n multilayers. The stimuli-responsive properties of these LbL films were examined by monitoring the adsorption of proteins by means of QCM-D and fluorescence measurements, while varying (i) temperature, (ii) pH, (iii) ionic strength, or (iv) a combination of the above parameters. It appears that all these stimuli strongly influence the amount of adsorbed proteins. In short, these new PNIPAM block copolymer-based LbL coatings are easy to build on substrates of various nature and geometry (including nanoporous membranes)
40
Luo, Xinhang. "Few-Layer MoS2 Thin Films Grown by Chemical Vapor Deposition." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417656899.
Full text
41
Martinez, Jimenez Mawin Javier 1985. "Mecanismos de condução em filmes nanoestruturados de óxidos de grafeno." [s.n.], 2017. http://repositorio.unicamp.br/jspui/handle/REPOSIP/330593.
Full textAbstract:
Orientador: Antonio Riul JúniorTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-09-02T19:37:47Z (GMT). No. of bitstreams: 1 Jimenez_MawinJavierMartinez_D.pdf: 7578838 bytes, checksum: def5bc65d8270856f55d63211e1e0f09 (MD5) Previous issue date: 2017
Resumo: Para alcançar alto desempenho em dispositivos e aplicações faz-se necessário uma melhor compreensão do comportamento de materiais a base de grafeno em nanoescala para otimização de design e fabricação. A síntese química é uma excelente rota alternativa para produzir compósitos em nanoestruturas bem definidas de tamanhos semelhantes, garantindo propriedades elétricas reprodutíveis para aplicações confiáveis. O grafeno, na forma de pontos quânticos (QDs, do inglês quantum dots) em dimensão zero e nanofolhas (NPLs, do inglês graphene nanoplateletes) bidimensionais (2D), são materiais emergentes com funcionalidades únicas promissoras para novas aplicações. Neste trabalho apresentamos um estudo detalhado dos mecanismos de transporte em nanoestruturas formadas pela técnica de automontagem por adsorção física (LbL, do inglês Layer-by-Layer) na forma de multicamadas, com controle de espessura em nível molecular. Os filmes LbL foram formados por óxido de grafeno reduzido (rGO) funcionalizado com diferentes polieletrólitos tanto na forma de QDs quanto nanofolhas. As caracterizações elétricas indicaram corrente limitada pela carga espacial em algumas amostras, e em outras arquiteturas moleculares, mecanismo de condução via Poole-Frenkel seguindo a lei de Mott dominada por saltos variáveis. A flexibilidade da técnica LbL aliada à dimensão dos materiais utilizados foram favoravelmente exploradas como um ajuste fino para controle da mobilidade de portadores dentro das nanoestruturas formadas. Foi observado em alguns casos uma condução planar no interior da camada contendo rGOs na estrutura LbL com mobilidade eletrônica efetiva de ~ 35 cm² V^-1 s^-1. Em outros casos um mecanismo de condução 3D (interplanar ao longo de toda nanoestrutura LbL) com mobilidade eletrônica de ~ 151 cm² V^-1 s^-1. Medidas em função da temperatura indicaram alta probabilidade de saltos randômicos entre ilhas condutoras de rGO distribuídas ao longo da camada contendo os pontos quânticos, que contribui para um maior tempo de trânsito dos portadores e, consequentemente, mobilidades menores. O oposto ocorre para as nanofolhas de rGO, que requerem maiores energias de ativação devido ao tamanho e presença de defeitos, resultando em caminhos condutores maiores e com maiores mobilidades
Abstract: To achieve high-performance in devices and applications it is important a better comprehension of the behavior at nanoscale of graphene-based materials to promote a rational design and fabrication. The chemical synthesis is an excellent alternative route to optimize graphene-based composites in well-defined nanostructures of similar sizes, ensuring reproducible electrical properties for reliable applications. Graphene as quantum dots (QDs) and nanoplatelets (NPLs) presents emerging zero- and two-dimensional (2D) materials with promising unique functionalities to novel applications. We present here a detailed study of the charge transport mechanisms in multilayered nanostructures formed by physical adsorption through the layer-by-layer (LbL) technique, with molecular level thickness control. The LbL films were formed by reduced graphene oxides (rGO) functionalized with different polyelectrolytes and processed either as QDs or nanoplatelets. The electrical characterizations indicated a space-charge-limited current (SCLC) in some samples, while in other molecular architectures it was found a Poole-Frenkel conduction mechanism dominated by a Mott-variable range hoping model. The LbL assembly together with the dimensionalty of the materials could be favorably used as a fine tuning to control the charge carrier mobility inside the formed nanostructures. The flexibility of the LbL technique together with the dimensionality of the materials were favorably explored as a fine tuning of the charge carrier mobility inside the nanostructures. It was observed in some cases a 2D intra-planar conduction within the rGO layer in the LbL films, with an effective charge carrier mobility of ~ 35 cm² V-1 s-1, and in other cases a 3D conduction mechanism (interplanar along with the LbL nanostructure) with electronic mobility of ~ 151 cm² V-1 s-1. Temperature measurements indicated a higher probability of random jumps between rGO conducting "islands" distributed along with the plane layer having quantum dots, which contributes for a longer transit time of the carriers and, consequently, lower mobility values. The opposite occurred for the rGO nanoplatelets that required higher activation energy due to size and presence of defects, resulting in larger conductive pathways and higher mobilities
Doutorado
Física
Doutor em Ciências
1247719
CAPES
FAPESP
42
Jesus, Cliciane Guadalupe de. "FILMES AUTOMONTADOS DO CLORETO DE 3-n-PROPILPIRIDÍNIO SILSESQUIOXANO E FTALOCIANINA DE COBRE OBTIDOS PELA TÉCNICA LbL: PREPARAÇÃO, CARACTERIZAÇÃO E APLICAÇÕES." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2009. http://tede2.uepg.br/jspui/handle/prefix/2064.
Full textAbstract:
Made available in DSpace on 2017-07-24T19:37:59Z (GMT). No. of bitstreams: 1
ClicianeGuadalupeJesus.pdf: 2429700 bytes, checksum: c3ac935bcc2b97480f80dc8cf9ff472d (MD5)
Previous issue date: 2009-02-27Nanostructured films composed by a 3-n-propylpyridinum silsesquioxane polymer (designated as SiPy+Cl-) and copper (II) tetrasulphophthalocyanine (CuTsPc) were produced using the Layer-by-Layer technique (LbL). The deposition of the bilayers was monitored by UV-Vis spectroscopy accompanying the absorbance of Q-band at 617 nm. It was observed that the absorbance linearly increased with the number of SiPy+Cl-/CuTsPc or CuTsPc/SiPy+Cl- bilayers, indicating that the same amount of material was deposited at each step of film formation. FTIR spectra showed that there is a specific interaction by the SO3 - groups of CuTsPc and the pyridinium groups of the polycation, SiPy+Cl-. Morphological studies of films surfaces showed that their roughness and thickness increase with the number of bilayers. The films were employed to detect dopamine (DA) and ascorbic acid (AA) using cyclic voltammetry. It was observed that the number and the sequence of bilayers deposition directly influenced on the electrochemical response in presence of the analytes. LbL films with lower number of bilayers (1 to 5 bilayers) presented higher current values in presence of the analytes, which is attributed to the higher facility of diffusion of target species to the electrode surface and enhancement of the efficiency of the electron transfer process. Considering the sequence of bilayers deposition, it was observed that the CuTsPc/SiPy+Cl- film did not show any redox peaks in the potential range -0.2 V to 1.6 V vs Ag/AgCl in presence of DA and AA. In contrast, the SiPy+Cl-/CuTsPc LbL film, presented a defined oxidation redox peak at approximately 1.2 V for DA and 0.8 V for AA, which linearly increased with DA concentration in HCl 1.0x10-3 molL-1 electrolyte solution (pH 3). Studies in different scan rates for the SiPy+Cl-/CuTsPc LbL film in presence of these analytes showed that the anodic peak current (Ipa) linearly increased with the square root of the scan rate (n1/2 ) which is a typical behavior for systems governed by a diffusion controlled mechanism. The relationship Ipa/ n1/2 vs n resulted in an exponential profile, confirming the existence of an electrocatalytical process for both AA and DA provided by CuTsPc in the LbL film. Using differential pulse technique, films comprising SiPy+/CuTsPc were able to distinguish between DA and ascorbic acid (AA), with a potential difference of approximately with 400 mV, in the concentration range of 9.0x10-5 to 2.0x10-4 molL- 1(in pH 3.0) and detection limits in the order of 10-5 molL-1.
Filmes nanoestruturados formados entre o polímero 3-n-propilpiridínio silsesquioxano (designado como SiPy+Cl-) e ftalocianina tetrasulfonada de cobre (II) (CuTsPc) foram produzidos usando a técnica Layer-by-Layer (LbL). A formação dos filmes foi monitorada por espectroscopia na região do UV-Vis, acompanhando-se a absorbância da banda Q da ftalocianina em 617 nm. Observou-se que a absorbância aumentou linearmente com o número de bicamadas para os filmes SiPy+Cl-/CuTsPc ou CuTsPc/SiPy+Cl-, indicando que a mesma quantidade de material foi depositado a cada bicamada depositada. Espectros FTIR mostraram que há interação específica entre os grupos SO3 - da CuTsPc e o anel piridínio do policátion, SiPy+Cl-. Estudos da morfologia da superfície dos filmes mostraram que a rugosidade média e espessura dos filmes aumentam de acordo com o número de bicamadas. Os filmes foram empregados para detectar DA e AA, utilizando-se a técnica de voltametria cíclica. Observou-se que o número de bicamadas e a seqüência de deposição das mesmas influenciam diretamente sobre a resposta eletroquímica na presença dos analitos. Filmes LbL com menor número de bicamadas (1 a 5 bicamadas) apresentaram maiores valores de corrente, fato este atribuído a maior facilidade de difusão das espécies à superfície do eletrodo, aumentando a eficiência do processo de transferência de elétrons. Com relação à sequência de deposição das bicamadas constatou-se que o filme CuTsPc/SiPy+Cl- não mostrou picos redox na faixa de potencial de -0,2 V a 1,6 V vs Ag/AgCl na presença de DA e AA. Enquanto que o filme SiPy+Cl-/CuTsPc, apresentou um pico de oxidação bem definido em aproximadamente 1,2 V, para DA e em 0,8 V para AA, o qual aumentou linearmente com a concentração dos analitos utilizando HCl como eletrólito suporte. Estudos em diferentes velocidades de varredura do eletrodo SiPy+Cl-/CuTsPc na presença dos analitos mostraram que a corrente de pico anódica (Ipa) aumenta linearmente com a raiz quadrada da velocidade de varredura (n1/2), indicando que o processo de transferência de elétrons é controlado pela difusão das espécies à superfície do eletrodo. A relação entre Ipa/n1/2 vs n, resultou numa curva exponencial, confirmando a existência do processo eletrocatalítico resultante da oxidação da DA e AA proporcionada pela CuTsPc. Utilizando-se a técnica de voltametria de pulso diferencial, o eletrodo SiPy+Cl-/CuTsPc foi capaz de distinguir AA e DA quando presentes numa mesma solução, com um diferença de potencial de aproximadamente 400 mV, no intervalo de concentração de 9,0x10-5 a 2,0x10-4 molL-1(em pH 3) e limites de detecção (LOD) da ordem de 10-5 molL-1.
43
Kitagawa, Igor Lebedenco. "Caracterização por espectroscopia vibracional de filmes "Layer-by-Layer" contendo ftalocianina, polímeros condutores e gomas naturais /." Presidente Prudente, 2009. http://hdl.handle.net/11449/99695.
Full textAbstract:
Orientador: Carlos José Leopoldo ConstantinoBanca: Aldo Eloizo Job
Banca: Patrícia Alexandra Antunes
Banca: Neri Alves
O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp
Resumo: Esta dissertação apresenta o estudo do crescimento (em escala nanométrica) e morfológica (em escala micrométrica) de filmes finos fabricados segundo a técnica Layer-by-Layer (LbL) contendo ftalocianina tetrasulfonada de níquel, polímeros condutores, o polímero poli(alilamina hidroclorada) (PAH), e gomas naturais. Três sistemas foram investigados: i) filmes LbL de NiTsPc e PAH; ii) filme LbL de NiTsPc, PAH e gomas naturais e iii) filmes LbL dos polímeros condutores polianilina (PANI) e poli(o-metoxianilina) (POMA) com gomas naturais. As gomas utilizadas neste trabalho foram extraídas das árvores cajueiro (Anacardium occidentale), chichá (Sterculia striata), caraia (Sterculia urens) e angico (Anadenanthera macrocarpa Benth). As caracterizações destes filmes foram realizadas por meio das técnicas de espectroscopia eletrônica utilizando absorção na região do ultravioleta-visível (UV-vis), espectroscopia vibracional por espalhamento micro-Raman e por absorção na região do infravermelho (IV) com transformada de Fourier (FTIR). Os resultados deste trabalho mostraram que, somente os filmes de NiTsPc e PAH em pH 8,5 e os filmes de NiTsPc, PAH e gomas naturais apresentaram crescimento controlado, uniformidade morfológica e química.
Abstract: This dissertation presents the study of growth (in nano-scale thickness) and morphology (micrometric scale) of thin films produced using the Layer-by-Layer technique (LbL) containing nickel tetrasulfonated phthalocyanine, conducting polymers, the polymer poly(allylamine hydrochloride) (PAH), and natural gums. Three systems were investigated: i) LbL films of NiTsPc and PAH; ii) LbL films of NiTsPc, PAH and natural gums and iii) LbL films of the conducting polymers polyaniline (PANI) and poly (o-methoxyaniline) (POMA) with natural gums. The gums used in this work were obtained from the cashew (Anacardium occidentale), chicha (Sterculia striata), caraia (Sterculia urens) and angico (Anadenanthera macrocarpa Benth) trees. The characterizations of the LbL films were made using the ultraviolet-visible (UV-vis) absorption spectroscopy, vibrational spectroscopy through micro-Raman scattering and Fourier Transform infrared (FTIR) absorption. The results showed that only the LbL films of NiTsPc and PAH at pH 8.5 and the LbL films of NiTsPc, PAH and natural gums present controlled growth and morphological and chemical uniformity.
Mestre
44
Herodotou, Stephania. "Zirconium doped zinc oxide thin films deposited by atomic layer deposition." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2013045/.
Full textAbstract:
Doped zinc oxide is of interest as a transparent conductive oxide (TCO), due to the abundance of its major constituents, its low resistivity, high transparency and wide bandgap. The current work focuses on the properties required for TCO applications including resistivity of ≤10-3 Ω•cm, carrier density of ≥1020 cm-3, and transparency >80% in the visible light. Zirconium (Zr4+) was chosen as the dopant in the current work due to its abundance, comparable ionic size to Zn and because it can act as a double donor providing up to two extra free electrons per ion when substituted for Zn2+. The doping process can be controlled using atomic layer deposition (ALD), with the doped films resulting in an increased conductivity. The films in the current work resulted in a minimum resistivity of 1.44×10-3 Ω•cm and maximum carrier density of 3.81×1020 cm-3 for films <100 nm thickness, having 4.8 at.% Zr concentration. The resistivity was further reduced after reducing the interfacial and grain boundary scattering (i.e. increase grain size), by increasing the overall film thickness. The resistivity of 7.5×10-4 Ω•cm, carrier mobility of 19.6 cm2V‒1s-1 and carrier density of 4.2×1020 cm-3 were measured for a 250 nm thick film with 4.8 at.% doping. The tuning of the carrier density via doping offers control over the optical gap due to the net effect of Burstein-Moss effect and bandgap renormalisation. This resulted to an increase of the optical gap from 3.2 eV for the un-doped ZnO to 3.5 eV for 4.8 at.% Zr-doped films. The average optical transparency in the visible/near IR range was as high as 91% for 4.8 at.% doped films. The thickness increase also resulted in a grain orientation shift from perpendicular to the substrate (i.e. polar c-plane orientation) to parallel (i.e. non-polar m-plane) due to the strain increase that forced the films to grow at a low strain energy direction. This offers the possibility of growing non-polarised films that show no piezoelectric field charge observed in polar oriented films. Therefore, controlling the grain size through the number of ALD cycles can effectively result in mobility and preferred orientation control, while the doping concentration controls the resistivity, optical bandgap and transparency of the films.
45
Aoki, Pedro Henrique Benites [UNESP]. "Filmes nanoestruturados de fosfolipídios como sistemas miméticos de membrana biológica para aplicação em sensores via sers e espectroscopia de impedância." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/99692.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0
Previous issue date: 2011-02-15Bitstream added on 2014-06-13T20:00:21Z : No. of bitstreams: 1
aoki_phb_me_bauru.pdf: 3726182 bytes, checksum: c582cd9cf1e3d2f3af8f65685764355e (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A presente dissertação de mestrado trata da fabricação de filmes ultrafinos (nanômetros de espessura) de fosfolipídios aniônicos (DPPG e CLP) e zwiteriônicos (DPPC e DOPC) utilizando as técnicas layer-by-layer (LbL) e Langmuir-Blodgett (LB), possibilitando assim a obtenção de filmes com diferentes arquiteturas moleculares. O objetivo principal foi explorar a aplicação destas diferentes arquiteturas moleculares na detecção do fármaco fenotiazínico azul de metileno (AM) em soluções diluídas. O crescimento linear, camada por camada, desses filmes foi verificado e monitorado por espectroscopia de absorção no UV-Vis. Verificou-se por FTIR que o crescimento dos filmes LbL e LB é determinado por interações eletrostáticas entre os fosfolipídios e o polieletrólito catiônico PAH utilizado como camada de suporte, favorecendo o crescimento dos filmes com fosfolipídios aniônicos. A morfologia foi analisada através de microscopias ópticas, AFM e MEV, revelando que os fosfolipídios estruturam-se como vesículas nos filmes LbL e monocamadas nos filmes LB. Filmes LbL e LB de fosfolipídios com diferentes espessuras foram então depositados sobre eletrodos interdigitados de Pt formando unidades sensoriais que foram aplicadas na detecção de AM via espectroscopia de impedância. Os resultados mostraram que as diferentes arquiteturas moleculares dos filmes LbL e LB levam a respostas elétricas distintas e permitem a detecção de AM em concentrações de nanomolar. A técnica SERS foi utilizada para obter informações estruturais do sistema AM/fosfolipídios nos níveis de diluição alcançados via espectroscopia de impedância. Para tanto, monocamadas LB foram depositados sobre filmes evaporados com 6 nm de Ag e nanopartículas de Ag foram dispersas no interior dos filmes LbL. A presença da Ag na forma de nanopartículas em ambos os casos permitiu a obtenção...
Thin films of anionic (DPPG and CLP) and zwiterionic (DPPC and DOPC) phospholipids with different molecular architectures were fabricated using the layer-by-layer (LbL) and Langmuir-Blodgett (LB) techniques. The main goal of this work was to explore the Application of these distinct molecular architectures in the detection of high diluted solutions of methylene blue (MB), a phenothiazine derivative drug. The linear growth, layer by layer, of these films was verified and monitored by UV-Vis absorption spectroscopy. It was found by FTIR that electrostatic interactions among the phosholipids and the supporting layer of PAH (cationic electrolyte) are the main driving force allowing the growth of the LbL and LB films, which favors the growth of the cationic phospholipids. The morphology was analyzed through optical microscopy, AFM and SEM, revealing that the phospholipids are structured as vesicles in the LbL films and as monolayers in the LB films. Different thickness of LbL and as monolayers in the LB filma containing phospholipids were deposited onto Pt interdigitated electrodes forming sensingn units applied in the detection of MB using impedance spectroscopy. The results showed that the different molecular architectures of the LbL and LB films take to different eletrical responses and allow the MP detection in concentrations of nanomolar. The SERS technique was applied to obtain structural information of the system MP/phospholipids at the dilution levels reached via impedance spectroscopy at the dilution levels reached via impedance spectroscopy. Then, LB monolayers were deposited onto 6nm of Ag evaporated films with and Ag evaporated films with and Ag nanoparticles were dispersed within the LbL films. The presence of Ag forming nanoparticles in both cases played a key role in achieving the MB SERRS signal allowing obtaining the detection in high dilution levels, approaching... (Complete abstract click electronic access below)
46
Perinotto, Angelo Cesar. "Estudo de birrefrigência fotoinduzida em filmes automontados de azopolímeros e azocorantes." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-11062008-095810/.
Full textAbstract:
Neste trabalho foi estudada a influência da arquitetura molecular e das condições de fabricação de filmes sobre a birrefringência fotoinduzida em filmes automontados de um azopolímero comercial PS-119 ou do corante Brilliant Yellow (BY) como espécies fotorreativas. Os filmes automontados foram fabricados a partir de seis policátions, a saber, poli(alilamina hidroclorada) (PAH), poli(c1oreto de dodecildimetilamônio) (PDAC) (com 3 massas molares diferentes), poli(etileno imina) (PEI) e dendrímero poli(amidoamina) geração 4 (PAMAM-G4). No processo de fabricação o substrato era imerso alternadamente em solução aquosa de policátions e poliânions nos pHs 4, 6 e 8. O crescimento dos filmes foi monitorado por espectroscopia UV-VIS. após cada etapa de adsorção. Um aumento linear do pico em 480 nm, atribuído a transição , indicou que a mesma quantidade de material era adsorvida em cada passo de deposição. A birrefringência foi opticamente induzida usando-se um laser de 532 nm Nd-YAG. Dentre as propriedades dos filmes automontados, a que mais variou de um sistema para outro foi o tempo de escrita característico, definido como o tempo necessário para atingir 50% da birrefringência máxima. Este tempo dependia do polieletrólito e do pH da solução de partida. Os filmes PEI/PS-119 em pH 8 e PDAC(HMW)/PS-119, em pH 4, PAWBY em pH 8, e PDAC(HMW)/BY em pH 4, forneceram os seguintes tempos característicos: 34 min, 0,5 min, 10 min e 3 s, respectivamente. Estas grandes variações nos tempos de escrita estão relacionadas as diferenças nas estruturas dos policátions, que determinam a intensidade das interações entre os polieletrólitos. Os baixos tempos para PDAC, por exemplo, são atribuídos as menores interações com o poliânion, já que a carga do PDAC, um sal quaternário, sofre efeito de blindagem por grupos CH3. Mencione-se que o tempo de escrita para os filmes automontados de PDACIBY é o menor já relatado para filmes automontados, sendo da mesma ordem de grandeza dos filmes obtidos por spin-coating ou técnica de Langmuir-Blodgett (LB). A birrefringência residual, após o desligamento do laser de escrita, foi superior a 78% em todos os sistemas estudados, demonstrando a utilidade de filmes automontados para dispositivos de memória óptica permanente.This work was aimed at investigating the influence of the molecular architecture and film fabrication on the photoinduced birefi-ingence of layer-by-layer (LbL) films containing the azopolymer PS 119® or the azodye Brylliant Yellow (BY) as photoreactive materials. The LbL films were produced with six polications, viz.: poly(allylamine hydrochloride) (PAH), poly(diallyldimethylammonium chloride) (PDAC) (with three different molecular weights), poly(ethy1eneimine) (PEI) and generation 4 dendrimer poly(amidoamine) (PAMAM-G4). They were prepared via the alternate immersion of a substrate into the polycationic and polyanionic aqueous solutions, at concentrations of 0.5 mg/mL at three pHs: 4, 6 and 8. The assembly of multilayers was monitored aRer each adsorption step by UV-VIS spectroscopy. A linear increase was observed in the peak at 480 nm, assigned to the transition of the azobenzene moiety, indicating that the same amount of material was deposited at each deposition step. Birefringence was optically induced in films using a 532 nm NdYAG laser. Among the LbL properties, the characteristic writing time - corresponding to the time to achieve 50% of maximum birefiingence - was the quantity that most varied with the materials and experimental conditions employed. The writing time was estimated as 34 min. for PEI/PS-119 with solution at pH 8 films, 0.5 min. for PDAC(HMW)/PS-119, pH 4 films, ca. 10 min. for PAWBY, pH 8 films and 3 s for PDAC(HMW)íBY, pH 4 films. These differences in writing times are probably related to the structural differences of the polycations, which determine the degree of interactions between polycation and polyanion. Indeed, interactions between polyanion and PDAC are expected to occur to a lesser extent (in comparison to the other films) due to the hindering promoted by the dimethyl group in the quaternary ammonium salt, minimizing the interaction with sulfonated groups from PS-119 or BY. With less interaction the azobenzene groups are more mobile, thus causing the writing time to be shorter for PDACIpolyanion films. It should be stressed that the writing time for PDAC/BY is the shortest ever reported for LbL films, being of the same order of magnitude of writing times in cast and Langmuir-Blodgett (LB) films. The residual birefringence, aRer the writing laser was switched off, was at least 78% for all systems, indicating that these LbL films are suitable for long-term optical memories.
47
Altay, Gizem. "Free Standing Layer-by-layer Films Of Polyethyleneimine And Poly(l-lysine) For Potential Use In Corneal Stroma Engineering." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613005/index.pdf.
Full textAbstract:
In this study we fabricated free standing multilayer films of polyelectrolyte complexes for potential use in tissue engineering of corneal stroma by using the layer-by-layer (LbL) approach. In the formation of these LbL films negatively charged, photocrosslinkable (methacrylated) hyaluronic acid (MA-HA) was used along with polycations polyethyleneimine (PEI) and poly(L-lysine) (PLL). Type I collagen (Col) was blended in with PLL for improving the water absorption and cell attachment properties of the films. It was shown that the LbL films could be easily peeled off from glass substrates due to the photocrosslinking of one of the LbL components, the hyaluronic acid. Film growth and composition were monitored with FTIR-ATR. Heights of peaks at 3383 cm-1, and 2958 cm-1increased along with the bilayer number confirming the polymer build-up. Film integrity and thickness were investigated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Films thicker than 5 bilayers (BLs) were found to be uniform in appearance and 10 BL (PEI/MeHA) films were calculated to be ca. 6 &mum thick. Atomic force microscopy (AFM) revealed that as the number of BLs increased, surface roughness decreased. Activity of methacrylated hyaluronic acid was shown by the increased resistance of photocrosslinked multilayer films against hydrolysis by hyaluronidase. Patterns could be created on the films by photocrosslinking further proving that the crosslinking step is successful. Since the ultimate goal was to construct a corneal stroma PEI/MA-HA films were tested with corneal stroma cells, keratocytes. Cell proliferation on PEI/MA-HA films was quite poor in comparison to TCPS. In order to improve the cell adhesion the tests were repeated with PLL/MA-HA. Collagen was added to decrease the hydrophilicity and introduce cell adhesion sequences (Arg-Gly-Asp, RGD) to improve cell proliferation on the films and thus PLL+Col/MA-HA films were also tested. Introduction of collagen to the PLL/MA-HA films was found to decrease water retention of the multilayer films and improve cell viability and proliferation. Col+PLL/MA-HA LbL thus appear to be a promising platform for tissue engineering, especially of corneal stroma.
48
Tian, Yayang. "Elaboration of New Layer by Layer (LbL) Fluorescent thin films and their functionalization for the sensitive detection of bacteria." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLN029/document.
Full textAbstract:
Les antibiotiques ont été utilisés pour le traitement des infections bactériennes depuis plus de 70 ans, sauvant des millions de vies. Cependant, leur mauvaise et sur-utilisation ont conduit à l’émergence de la résistance bactérienne. Outre le développement de nouvelles familles d'antibiotiques, la détection rapide et sensible de bactéries est très importante pour le diagnostic médical. Les polymères fluorescents représentent un grand potentiel, car ils sont faciles à fonctionnaliser, synthétiser et greffer. Les films sont plus pratiques, faciles à manipuler et peuvent être réutilisés, ce qui n'est pas le cas des méthodes de détection en solution. L’objectif de ce travail est de développer un film de polymère nanostructuré fluorescent et sensible sur des surfaces de verre pour la détection bactérienne. Sur la base de la méthode de polymérisation radicalaire par transfert de chaîne réversible par addition-fragmentation (RAFT), trois types de polyélectrolytes fluorescents à base de BODIPY (FPC) ont été synthétisés : des chaînes relativement courtes à caractère polyélectrolyte faible (SW FPC), des chaînes courtes à caractère polyélectrolyte fort (SS FPC) et enfin des chaînes longues à caractère polyélectrolyte faible (FPC LW). Les films FPC LbL ont été élaborés sur des lames en verre par interaction électrostatique. Les propriétés photophysiques et de surface des FPC LbL ont été contrôlées en ajustant les conditions de dépôt. Les films FPC LbL à base de BODIPY ont été utilisés comme dispositif de première génération pour la détection de E. coli. Dans l'étape suivante, la sensibilité des films a été augmentée en utilisant le principe de fluorescence exaltée par plasmon (Metal Enhanced Fluorescence MEF). Un film LbL -MEF a été préparé et testé pour la détection de bactéries. Des nanoparticules d'or sphériques (Au NPs) ont été synthétisées et recouvertes de poly(chlorhydrate d'allylamine) (PAH). Le FPC LW a été sélectionné comme couche fluorescente. Différents films contenant des Au NPs et LW FPC- ont été fabriqués. La distance entre les NPs Au et LW FPC- a été ajustée par l'ajout de deux polymères de charge opposée (PC + et PC-). Les deux surfaces de AuNP / 4 couches PC / LWFPC- et Au NPs / 8 couches PC / LWFPC- ont montré que E. coli peut être ciblée par LW FPC-.La sélectivité des films LbL a été ajoutée en introduisant un anticorps comme site de reconnaissance spécifique. Le polyanion et le polycation avec le groupe fonctionnel 4-dibenzocyclooctynol (DIBO) ont été assemblés sur des lames de verre activées. L'anticorps anti-E. coli a ensuite été introduit sur la surface en une seule étape via la réaction de cycloaddition azide-alcyne (SPAAC). Le nombre d'E. coli capturées dépend de la concentration d’anticorps sur la surface. La surface a montré une sélectivité significative pour E. coli, comparée à B. subtilis.La croissance bactérienne peut être détectée sur un film mince LbL en introduisant un fluorophore sensible au pH (fluorescéine). En effet, la croissance des bactéries est souvent associée à une diminution du pH du milieu due à une libération de métabolites acides. Nous avons préparé avec succès différents types de films LbL sensibles au pH. Dans un premier temps, la synthèse de différents polyanions fonctionnalisés (chaîne courte et longue de DIBO-PC et polymère fluorescent rouge) a été achevée. Ensuite, trois types de surfaces sensibles au pH contenant de la fluorescéine (DIBO-SWPC- / fluorescéine, DIBO-LW PC- / fluorescéine et ratiométrique RFPC- / fluorescéine) ont été préparés sur la base d'assemblage LbL et de chimie click. Enfin, trois surfaces sensibles au pH ont été étudiées pour la détection de la croissance des bactéries. Toutes les surfaces étaient biocompatibles, le nombre de E. coli augmentait même après plusieurs heures d'incubation sur chaque surface. La détection par le changement de fluorescence est en cours de développementAntibiotics have been used for the treatment of bacterial infections for over 70 years, saving millions of lives. The current antibiotic resistance crisis has been attributed to the overuse and misuse of these medications. Therefore, the prevention of infection transmission by the rapid and sensitive detection of antibiotic resistant strains is needed in managing this crisis. Fluorescent polymers show great potential for bacteria detection, because they are easy to functionalize, reproduce and graft. Compared with the methods used for bacterial detection in liquid, bacterial detection on a film surface is more convenient, easier to handle and is applied in devices that can be easily reused. The goal of my PhD work is to develop fluorescent and sensitive nanostructured polymer films on surfaces for bacterial detection. Three types of BODIPY-based fluorescent polyelectrolytes (FPC) with different features were synthetized based on reversible addition-fragmentation transfer (RAFT) polymerization: relatively Short chains and Weak polyelectrolytes (SW FPC), Short chains and Strong polyelectrolytes (SS FPCs) and Long chains and Weak polyelectrolytes (LW FPCs). FPC LbL films were fabricated on activated glass slides by means of electrostatic attraction. The photophysical and surface properties of FPC LbL fims were easily controlled by adjusting the deposition conditions.The following step aimed at increasing the films’ sensitivity by using the metal-enhanced fluorescence (MEF) principle. A MEF based LbL film was prepared and tested for bacteria detection. Spherical gold nanoparticles (Au NPs) were synthesized and coated with poly(allylamine hydrochloride) (PAH). The LW FPC- was selected as the fluorescent layer. Different films containing Au NPs and LW FPC- were fabricated and the distance between the Au NPs and LW FPC- was adjusted by changing the numbers of layers with two oppositely charged polymers (PC+ and PC-). Both Au NPs/4 layers PCs/LWFPC- and Au NPs/8 layers PCs/LWFPC- surfaces indicated that E. coli can be detected by LW FPC-.The selectivity of LbL films was added by introducing an antibody on the surface of the film to provide specific recognition of a chosen bacterial strain. This LbL surface achieved a rapid, effective and specific detection of E. coli bacteria. The polyanion and polycation with a 4-dibenzocyclooctynol (DIBO) functional group were assembled on the activated glass slides and an anti-E. coli antibody containing an azide group was efficiently introduced on the surface in a single step based on the azide-alkyne cycloadditions (SPAAC) reaction. The number of E. coli captured on the surface was shown to be dependent on the amount of antibody on the surface. The anti-E. coli antibody surface showed significant selectivity for E. coli, compared with B. subtilis. An alternative approach is to detect bacterial growth on thin LbL film by introducing pH sensitive fluorophore (fluorescein). The growth of bacteria is often associated with a decrease in pH of the growth medium due to a release of acidic metabolites. Different types of pH sensitive LbL film were prepared and tested for the detection of bacterial growth. Firstly, the synthesis of different functionalized polyanions (short and long chain of DIBO-PC- and red fluorescent polymer) was carried out. Three types of pH sensitive surfaces containing fluorescein (DIBO-SWPC-/fluorescein, DIBO-LW PC-/fluorescein and ratiometric RFPC-/fluorescein surfaces) were prepared based on the combination of LbL assembly and copper-free click chemistry. Finally, three pH sensitive surfaces were studied for bacteria growth detection. All the surfaces were shown to be biocompatible, the number of E. coli increased after several hours of incubation on each surface, as detected by brightfield microscopy imaging. The application for the fluorophore-dependent detection of bacterial growth remains to be developed
49
Liu, David ShinRen. "Controlling the mechanical and transport properties of layer-by-layer films and electrospun mat composite membranes for fuel cell applications." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91061.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
There is an ever increasing need for clean, portable energy devices, such as fuel cells and high energy batteries to replace or reduce the world's dependence on fossil fuels. The continued development of thin-film solid polymer electrolytes with improved mechanical and ion transport properties is critical for the further advancement of such electrochemical energy devices. For hydrogen and methanol fuel cells, the proton exchange membrane (PEM) has to have high protonic conductivity, low fuel crossover, and be mechanically and chemically stable. In particular, for direct methanol fuel cells and for high temperature (>100 °C), low relative humidity (< 60% RH) hydrogen fuel cells, the current industrial standard PEM, Nafion®, does not have all the required attributes. Layer-by-Layer (LbL) assembly allows for the controlled deposition of alternating polyelectrolytes at the nanometer scale. This technique can be used with highly proton conductive water soluble polymers as well as doped polymers. In addition, LbL assembly can be used to coat a variety of substrates of various shapes and sizes. An LbL system composed of poly(diallyl dimethyl ammonium chloride) (PDAC) and sulfonated poly(2,6-dimethyl 1,4- phenylene oxide) (sPPO) has shown to have relatively high proton conductivity and very low methanol permeability compared to that of Nafion@, but lacking in mechanical strength when hydrated and losing significant proton conductivity at lower RH conditions. Herein this thesis work describes the selection, optimization, and utilization of multilayer systems and system composites as the PEM in hydrogen and methanol fuel cells, focusing on improving and understanding the improvements to the properties of layer-by-layer films and composite membranes for fuel cell applications by targeting two main areas: the mechanical properties and the conductive properties. In addition, characterization and film analysis work was done to correlate and explain how the changing of the LbL system and fabrication techniques impacted the membrane's mechanical and conductive properties. First, the mechanical strength and stability were greatly improved by spray-assembling the films on an electrospun fiber mat to form a composite membrane. Spray-LbL assembly was performed both with and without vacuum assistance, which had complementary effects on the film properties. By combining these techniques, composite membranes with methanol permeability twenty times lower than Nafion® and through-plane proton selectivity five times greater than Nafion@ were fabricated. In addition, the planar swelling of the composite membranes in water was significantly reduced. This large reduction in swelling is hypothesized to be due to the electrostatic interaction of the LbL system with the underlying electrospun fibers and would not occur in a typical polymer blend. Second, to improve the conductivity of the LbL films overall and specifically at lower RH conditions, two approaches were used. In the first approach, divalent salts were added to the polyanion solution to provide a stronger shielding effect than monovalent salts. The divalent salts allowed for ion bridging and increased both the number and the mobility of protons associated with sulfonic acid groups in the LbL film; thus increasing the film's conductivity. Through optimization of salt type and concentration, the protonic conductivity of PDAC/sPPO films was increased fourfold, and the humidity dependence of the conductivity was decreased. In the second approach, PDAC was replaced with a phosphoric-acid-doped polymer, poly(2- vinyl pyridine) (P2VP). The phosphoric acid concentration in the LbL film and the number of free sulfonic acid groups could be controlled post film fabrication by changing the concentration of the phosphoric acid dopant. The resulting P2VP/sPPO films exhibited greater conductivity than similarly doped P2VP films and under stronger doping conditions (0.4 M - 1.0 M phosphoric acid), the film's conductivity increases seventy-fivefold (110 mS/cm at 50% RH at room temperature), resulting in a conductivity an order of magnitude greater than Nafion®. The large increases in conductivity, particularly at low RH conditions further support a recently reported and very promising proton transport mechanism that utilizes both phosphoric and sulfonic acid groups.
by David ShinRen Liu.
Ph. D.
50
Puckett, Sean D. "Techniques for the Detection and Development of: Part I Detection of Ozone for Water Treatment Part II. Utilizing Layer-By-Layer Thin Films with Long Period Grating Fibers." Oxford, Ohio : Miami University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1146248790.
Full text