Dissertations / Theses on the topic 'Nanoparticles - Functional Properties'

This thesis focuses on the shape-controlled metal nanoparticles for functional applications, covering the synthesis, characterization and optical properties. Three parts are mainly involved in this work, including, gold worm-like nanoparticles, silver nanoplates, and silver induced selenium nanowires. The first part focuses on a facile synthesis method for shape control of gold nanoparticles by treating an aqueous solution of chloroauric acid with sodium citrate and poly(vinyl pyrrolidone) (PVP), in which those worm-like nanoparticles were investigated by various advanced experimental characterizations combining density function theory (DFT) calculation. These nanoparticles can be used for optical sensing detection of ions in aqueous system. The second part involves the synthesis, growth, and optical properties of silver nanoplates (triangles and circular discs). Such nanoplates could be synthesized by a self-seeding co-reduction method at ambient conditions. In particular, molecular dynamics simulation is used to quantify the interaction energies between surfactant molecules and different facets of silver crystal. Such molecular information, together with measurements using x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and ultraviolet??visible (UV??vis) spectroscopy, has proven to be useful for understanding the growth mechanisms of silver nanoplates. The third part focuses on the template of silver nanoparticles for generating trigonal selenium (t-Se) nanowires. This technique exhibits some advantages in fabricating t-Se nanostructures, including no need to use stabilizers and sonichemical process and all operations being proceeded in aqueous media and at room temperature. Particularly it can successfully achieve the transformation from amorphous α-Se to crystalline t-Se in aqueous solution and this method would be useful for generating one-dimensional nanostructures with similar lattice parameter(s). It is considered that the technique for the shape-controlled metal nanoparticles can at least partially, be extended to other nanomaterials for functional applications.

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
The remarkable optical and luminescence properties of noble metal nanoparticles (with diameters < 2 nm) attract researchers due to potential applications in biomedicine, photocatalysis, and optoelectronics. Extensive experimental investigations on luminescence properties of thiolate-protected gold and silver nanoclusters during the past decade have failed to unravel their exact photoluminescence mechanism. Herein, density functional and time-dependent density functional theory (DFT and TDDFT) calculations are performed to elucidate electronic-level details of several such systems upon photoexcitation. Multiple excited states are found to be involved in photoemission from Au₂₅(SR)₁₈– nanoclusters, and their energies agree well with experimental emission energies. The Au₁₃ core-based excitations arising due to electrons excited from superatom P orbitals into the lowest two superatom D orbitals are responsible for all of these states. The large Stokes shift is attributed to significant geometrical and electronic structure changes in the excited state. The origin of photoluminescence of Ag₂₅(SR)₁₈– nanoclusters is analogous to their gold counterparts and heteroatom doping of each cluster with silver and gold correspondingly does not affect their luminescence mechanism. Other systems have been examined in this work to determine how widespread these observations are. We observe a very small Stokes shift for Au₃₈(SH)₂₄ that correlates with a relatively rigid structure with small bond length changes in its Au₂₃ core and a large Stokes shift for Au₂₂(SH)₁₈ with a large degree of structural flexibility in its Au₇ core. This suggests a relationship between the Stokes shift of gold−thiolate nanoparticles and their structural flexibility upon photoexcitation. The effect of ligands on the geometric structure and optical properties of the Au₂₀(SR)₁₆ nanocluster is explored. Comparison of the relative stability and optical absorption spectra suggests that this system prefers the [Au₇(Au₈SR₈)(Au₃SR₄)(AuSR₂)₂] structure regardless of whether aliphatic or aromatic ligands are employed. The real-time (RT) TDDFT method is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems. A systematic benchmark study is performed to demonstrate the consistency of linear-response (LR) and RT-TDDFT methods for calculating the optical absorption spectra of a variety of bare gold and silver nanoparticles with different sizes and shapes.

Cerium dioxide (ceria) is an excellent catalytic material due to its ability to both facilitate oxidation/reduction reactions as well as store/release oxygen as an oxygen buffer. The traditional approach to assess and improve ceria's catalytic behavior focuses on how efficiently O-vacancies can be generated and/or annihilated within the material, and how to extend established understandings of "bulk" ceria to further explain the greatly enhanced catalytic behavior of ultra-small ceria nanoparticles (uCNPs) with sizes less than 10 nm. Here, using density functional theory (DFT) calculations, we reexamine the atomic and electronic structures of uCNPs, especially their surface configurations. A unique picture dissimilar to the traditional point of view emerges from these calculations for the surface structure of uCNPs. uCNPs similar to those obtained by experimental synthesis and applied in catalytic environments exhibit core-shell like structures overall, with under-stoichiometric, reduced CNP "cores" and over-stoichiometric, oxidized surface "shell" constituted by various surface functional groups, e.g.,-Ox and/or -OH surface groups. Therefore, their catalytic behavior is dominated by surface chemistry rather than O-vacancies. Based on this finding, reaction pathways of two prevalent catalytic reactions, namely CO oxidation and the water-gas shift reaction over uCNPs are systematically investigated. Combined, these results demonstrate an alternative understanding of the surface structure of uCNPs, and provide new avenues to explore and enhance their catalytic behavior, which is likely applicable to other transition metal oxide nanoparticles with multivalent ions and very small sizes.

In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.

In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.

Optical properties of nanocluster-based plasmonic materials were studied along this thesis by the Generalized Multiparticle Mie approach. Far- and local-field optical properties of basic plasmonic structures such as sphere dimers and chains were successfully analyzed as a function of their composition and their topological features. The provided physical insight is then exploited in the modeling of strongly coupled complex structures obtained by ion beam processing. These systems were called nanoplanets since they are constituted by a large central cluster surrounded by small satellite ones very close to its surface. Nanoplanets show extremely interesting far- and local-field properties which may be carefully tailored by varying the ion beam synthesis conditions. GMM theory allowed to establish that the strong interparticle coupling is at the base of their peculiar optical features. Finally multiple coupled cluster are proposed as efficient nanoantennae. Nanoparticle dimers were proved to provide extremely efficient broadband light extraction. If regular sphere array are used instead, broadband limitation imposed by isolated antennae may be overcome and tunable wavelength selective recombination rate enhancement is obtained. Overall this thesis gives an interesting insight in the plasmonic properties of functional multiple coupled cluster nanostructures.

The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the  bottom-up approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a variety of theoretical and computational tools with different degrees of accuracy to study problems in different time and length scales. Interactions between the atoms are derived using both Density Functional Theory (DFT) and Embedded Atom Method (EAM), depending on the scale of the problem at hand. For some cases, both methods are used for the purpose of comparison. For revealing the local contributions to the vibrational dynamics and thermodynamics for the systems possessing site-specific environments, a local approach in real-space is used, namely Real Space Green s Function method (RSGF). For simulating diffusion of atoms/clusters and growth on metal surfaces, Molecular Statics (MS) and Molecular Dynamics (MD) methods are employed.
Ph.D.
Department of Physics
Sciences
Physics PhD

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
Small silver and gold clusters (less than 2 nm) display a discrete absorption spectrum characteristic of molecular systems whereas larger particles display a strong, broad absorption band in the visible. The latter feature is due to the surface plasmon resonance, which is commonly explained by the collective dipolar motion of free electrons across the particle, creating charged surface states. The evolution between molecular properties and plasmon is investigated. Time-dependent density functional theory (TDDFT) calculations are performed to study the absorption spectrum of cluster-size silver and gold nanorods. The absorption spectrum of these silver nanorods exhibits high-intensity longitudinal and transverse modes (along the long and short axis of the nanorod respectively), similar to the plasmons observed experimentally for larger nanoparticles. These plasmon modes result from a constructive addition of the dipole moments of nearly degenerate single-particle excitations. The number of single-particle transitions involved increases with increasing system size, due to the growing density of states available. Gold nanorods exhibit a broader absorption spectrum than their silver counterpart due to enhanced relativistic effects, affecting the onset of the longitudinal plasmon mode. The high-energy, high-intensity beta-peak of acenes also results from a constructive addition of single-particle transitions and I show that it can be assigned to a plasmon. I also show that the plasmon modes of both acenes and metallic nanoparticles can be described with a simple configuration interaction (CI) interpretation. The evolution between molecular absorption spectrum and plasmon is also investigated by computing the density of states of spherical thiolate-protected gold clusters using a charge-perturbed particle-in-a-sphere model. The electronic structure obtained with this model gives good qualitative agreement with DFT calculations at a fraction of the cost. The progressive increase of the density of states with particle size observed is in accordance with the appearance of a plasmon peak. The optical properties of nanoparticles can be tuned by varying their composition. Therefore, the optical behavior of the bimetallic Au[subscript](25-n)Ag[subscript]n(SH)[subscript]18[superscript]- cluster for different values of n using TDDFT is analyzed. A large blue shift of the HOMO-LUMO absorption peak is observed with increasing silver content, in accordance with experimental results.

This doctoral Thesis has been focused on the preparation of magnetic materials by different methods, the characterization of their structural characteristics, and the understanding of their mechanical and magnetic properties. Furthermore, a big effort has been paid to investigate the frequency-dependent functional properties of different materials, which are increasingly demanded in novel technological applications. Moreover, this work presents this characterization in a wide range of frequencies, from the kHz to the THz. In the first chapter, the reader will find an introduction to the topic and the state of the art of those materials that have been synthesized and developed in this Thesis. Then, the general goals of our research are described. Chapter II provides all the needed fundamental theory to accomplish with the previously stated goals. The concepts exposed here will be used later in the following chapters where the results will be shown and discussed. Moreover, this chapter does not only pretend to give the essential notions used in the following chapter, but we also aim to provide a useful guide to anyone who starts working on this field. All the materials, devices, software, and experimental conditions used in this Thesis are described in Chapter III. Here, we describe these aspects in detail in order to allow an agile discussion in the following chapters. The first experimental chapter is Chapter IV, where the synthesis of copper ferrite nanoparticles by mean of sol-gel and co-precipitation is described. The sol-gel process is optimized through of design of experiments (DoE) approach. The results of the mechanical and magnetic characterization of solid pellets fabricated with the previously synthesized nanoparticles are also shown in this chapter. Finally, by using statistical methods a direct experimental correlation between the mechanical and magnetic properties is found in this material. Another material, a carbon nanotube–based nanocomposite, is studied in Chapter V. This novel material is first structurally characterized in order to understand its magnetic properties. A big effort is paid on the study of the magnetic relaxation of this material, which has not been previously reported as far as we know. The investigation of soft magnetic materials (SMM) and composites (SMC) can be found in Chapter VI. The actual SMCs are first structurally and magnetically characterized. Their magnetic properties in the kHz and MHz frequency range are also investigated, showing the better performance of the SMC at high frequencies. In the second part of the chapter, the development on new SMC’s formulations is described. The developed materials are potentially useful for applications in the kHz and MHz frequency range. The frequency is raised in Chapter VII. Terahertz time-domain spectroscopy (THz-TDS) is used to investigate the optical and dielectric properties of two different semiconductor oxides from 180 GHz to 3 THz. The signal processing and the interpretation of the effect that different characteristics of the sample may have on the observed properties are discussed. In this chapter, magnetic materials are not investigated because the Fresnel model – which is the base of this technique - assumes a non-magnetic response of the material. The work described in Chapter VIII is completely different from the previous ones. In this case, we investigate the manipulation of the magnetic moments by using surface acoustic waves (SAWs). The experiments done in this chapter lead to interesting observation about the potentiality of the use of SAWs to accelerate the magnetic moment reversal in magnetic nanoparticles.
Esta Tesis Doctoral se centra en el estudio de materiales magnéticos en su conjunto, tanto desde la síntesis hasta sus propiedades mecánicas y funcionales finales. Además, ha habido un especial interés en el estudio de las propiedades funcionales en un amplio rango frecuencial. De este modo, en el primer capítulo, el lector puede encontrar una introducción al campo de investigación, así como también el estado del arte de aquellos materiales que se han sintetizado y desarrollado en esta Tesis. Por otro lado, en el Capítulo II se aportan todos los conceptos teóricos necesarios para el siguiente desarrollo de la Tesis. Además, los materiales, dispositivos, software y condiciones experimentales utilizados durante el desarrollo de esta investigación están descritos en el Capítulo III. El Capítulo IV es la primera parte experimental de la Tesis, y en la que se describe la síntesis de nanopartículas de ferrita de cobre vía sol-gel y coprecipitación. Además, se estudian las propiedades magnéticas y mecánicas en bulk, y se analiza su correlación empírica. El Capítulo V está dedicado al estudio de un nuevo material: un nanocompuesto magnético basado en nanotubos de carbono. Inicialmente se caracteriza química y estructuralmente para después centrarse en las propiedades magnéticas. Se realiza, además, un detallado estudio de su relajación magnética. Por otro lado, en el Capítulo VI, se investigan materiales magnéticos blandos. Inicialmente se analizan los materiales actualmente utilizados, mientras que en una segunda parte se desarrollan nuevas formulaciones con interesantes propiedades tecnológicas. En el Capítulo VII se presenta el estudio de las propiedades ópticas y dieléctricas en el rango de los THz. Se describe detalladamente el método, análisis de señal, y efecto de las características físicas de la muestra sobre la medida. Finalmente, también se propone un método para cuantificar el efecto de la porosidad de las muestras. Por último, el Capítulo VIII se investiga la manipulación del momento magnético mediante estímulos mecánicos como las ondas acústicas superficiales (SAW, en inglés). Se observa una clara variación experimental con la aplicación de las SAWs, y se relaciona matemáticamente esta variación con la frecuencia y potencia de las SAWs.

Doctor of Philosophy
Department of Chemistry
Christine M. Aikens
Gold and silver particles with dimensions less than a nanometer possess unique characteristics and properties that are different from the properties of the bulk. They demonstrate a non–zero HOMO–LUMO gap that can reach up to 3.0 eV. These differences arise from size quantization effects in the metal core due to the small number of atoms. These nanoparticles have attracted great interest for decades both in fundamental and applied research. Small gold clusters protected by various types of ligands are of interest because ligands allow obtaining gold nanoclusters with given sizes, shapes and properties. Three main families of organic ligands are usually used for stabilization of gold nanoclusters: phosphine ligands, thiolate ligands and DNA. Usually, optical properties of these NPs are studied using optical absorption spectroscopy. Unfortunately, sometimes this type of spectrum is poorly resolved and tends to appear very similar for different complexes. In these cases, circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopy can be applied. However, the interpretation of experimental CD and MCD spectra is a complicated process. In this thesis, theoretically simulated CD and MCD spectra were combined with optical absorption spectra to study optical activity for octa– and nona– and undecanuclear gold clusters protected by mono– and bidentate phosphine ligands. Additionally, optical properties of bare and DNA protected silver NPs were studied. Theoretical CD spectra were examined to learn more about the origin of chirality in chiral organometallic complexes, and to contribute to the understanding of the difference in chiroptical activity of gold clusters stabilized by different phosphine ligands and DNA–stabilized silver clusters. Furthermore, optical properties of the small centered gold clusters Au₈(PPh₃)₈²⁺ and Au₉(PPh₃)₈³⁺ were examined by optical absorption and MCD spectra using TDDFT. Theoretical MCD spectra were also used to identify the plasmonic behavior of silver nanoparticles. These results showed that CD and MCD spectroscopy yield more detailed information about optical properties and electronic structure of the different chemical systems than optical absorption spectroscopy alone. Theoretical simulation of the CD and MCD spectra together with optical absorption spectra can be used to assist in the understanding of empirically measured CD and MCD and provide useful information about optical properties and electronic structure.

We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl3, CoCl2, CuCl2, and MnCl2. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have considerable internal strain, resulting in clearly visible lattice distortions in bright and dark-field transmission electron micrographs. Photo and electroluminescence studies indicate that the strain-induced defects strongly dominate any dopant-related effects. However, annealing at moderate temperature as well as laser annealing induces strain relaxation and leads to dopant activation. Hence, the optical and electrical properties of the nanowires significantly improve, allowing these nanowires to become feasible for use in the fabrication of solar cell and LED devices. In addition, the magnetic impurities incorporated into our ZnO nanowires show superparamagnetic behavior at room-temperature, while Al-doped and undoped ZnO nanowires show no magnetic behavior. The electroluminescence (EL) is achieved from a vertical hybrid p-n junction LED arrangement consisting of a hole-conducting polymer and n-type ZnO nanowires, our group was the first to report this vertical nanowire-based LED in Könenkamp et al., 2004 [12]. The observed EL spectra show an ultraviolet excitonic emission peak and a broad defect-related emission band in the visible range. After annealing at 380° C, the defect related EL peak exhibits a characteristic shift to higher wavelengths, where the magnitude of the shift is dependent on the dopant type. Aluminum incorporation exhibited the most improved exciton related-emission, leading to the emergence of a narrow excitonic luminescence peak around 390 nm, which is close to the bandgap of ZnO. The comparison of spectra obtained from temperature-dependent photoluminescence (PL) measurements, before and after thermal annealing, also indicates that the optical activity of impurities changes noticeably upon annealing. The internal quantum efficiency for PL is measured to be as high as 16 percent for Al-doped samples annealed at 380° C. The PL measurements also show that the excitonic luminescence is preferentially guided, while the defect related emission is more isotropically emitted. The nanostructured heterojunction solar cell is designed such that thin CdSe quantum dot films are embedded between a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and an efficient collection of photogenerated carriers. Here, we present a detailed analysis of the pyridine solution and 1,2- ethanedithiol ligand exchange processes of the quantum dots, deposition processes of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal annealing process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous poly-crystalline film, with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the CdSe layer. The combination of the solution and ligand exchange of CdSe quantum dots, as well as the deposition and optimized annealing processes of this quantum dot layer, resulted in solar cells with an open-circuit voltage up to 0.6 V, a short circuit current of ~15 mA/cm2, an external quantum efficiency of 70 percent, and an energy conversion efficiency of 3.4 percent. This 3.4 percent efficiency is presently one of the best efficiencies obtained for this type of device.

Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is considered
Tiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille
Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., & Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., & Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., & Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046

Os problemas ambientais provocados pelas embalagens à base de materiais sintéticos não biodegradáveis têm provocado um importante aumento nos estudos sobre filmes à base de biopolímeros. Entretanto, esses filmes têm limitações em suas propriedades, devido, sobretudo à sensibilidade a umidade relativa ambiente. Dentre as alternativas estudadas para melhorar as características desses materiais está o uso de nanopartículas, com destaque para a montmorilonita, que tem problemas de dispersão em água. Outra nanopartícula pouco usada em estudos à base de biopolímeros é a laponita, que é uma nanoargila sintética. Assim, o objetivo geral desta tese foi o desenvolvimento de filmes à base de biopolímeros (colágeno, gelatina e fécula de mandioca), reforçados com uma nanoargila (laponita). Foi estudado o efeito da concentração do biopolímero e da laponita, assim como o método de produção dos filmes (casting e espalhamento mecânico), além da qualidade da dispersão da nanopartícula, sobre as principais propriedades físicas dos filmes nanocompósitos, com especial interesse nas propriedades de superfície. Os filmes foram preparados pela desidratação de soluções formadoras de filmes (SFF), com 2, 4 ou 8 g de biopolímero/100 g SFF; 25 ou 30 g glicerol/100 g de biopolímero; e 0, 1,5; 3; 4,5 e 6 g laponita/100 g de biopolímero. A laponita foi dispersa em água destilada, utilizando-se ultraturrax com velocidade de agitação de 20.000 rpm, por 30 minutos. As partículas de laponita em água tiveram tamanhos menores que 50 nm. Não houve efeito da concentração do biopolímero, nem do método de produção (casting ou espalhamento mecânico) sob as propriedades de topografia superficial e físico-químicas estudadas nos filmes nanocompósitos. As análises de raios X e espectroscopia de infravermelho por transformada de Fourier revelaram que as plaquetas de laponita estiveram esfoliadas e/ou intercaladas nos filmes, e que não houve nenhuma formação de ligação química entre as plaquetas de laponita e os biopolímeros em estudo. A presença de laponita incrementou a irregularidade superficial dos filmes, especialmente naqueles produzidos com colágeno e fécula de mandioca. Outras propriedades dos filmes nanocompósitos, tais como densidade, umidade, cor, opacidade, propriedades térmicas, propriedades mecânicas, solubilidade em água, ângulo de contato à água, isotermas de sorção e permeabilidade ao vapor de água não sofreram alterações com a presença de laponita.
The environmental problems caused by packaging based on non-biodegradable synthetic materials have lead to a significant increase in studies about biopolymer films. However, these films have limited physicochemical properties due mainly to its sensitivity to ambient relative humidity. Among the alternatives studied to improve the physicochemical properties of these materials is the use of nanoparticles, especially the montmorillonite, which has problems of dispersion in water. Another nanoparticle no so much studied in films based on biopolymers is laponite, which is a synthetic nanoparticle. Thus, this these aims to development and characterize films based on biopolymers (collagen, gelatin and cassava starch), with a nanoparticle (laponite). The effects of biopolymer and laponite concentrations were studied, as well as, the film production method (casting and spreading), besides the quality of laponite dispersion and its relationship with the physicochemical properties of the films were investigated, with special interest on the surface properties. The films were produced by the dehydration of filmogenic-forming solutions (FFS), with 2, 4 or 8 g of biopolymer/100 g FFS; 25 or 30 g glycerol/100g of biopolymer; and 0, 1.5, 3, 4.5 and 6 g of laponite/100g of biopolymer. The laponite was dispersed in water using ultraturrax, at 20,000 rpm, for 30 minutes. The laponite particles in water had sizes smaller than 50 nm. There was not effect of biopolymer concentration and film production method (casting or spreading) on the surface and physicochemical properties studied in the nanocomposite films. X-ray analysis and Fourier transform infrared spectroscopy revealed that laponite platelets were exfoliated and/or intercalated in the films, and that there were no formed chemical bonds between laponite platelets and the biopolymers studied. The presence of laponite increased the surface irregularity of the films, especially in those produced with collagen and cassava starch. Other properties in the nanocomposite films, such density, moisture content, color, opacity, thermal properties, mechanical properties, water solubility, water contact angle, sorption isotherms and water vapor permeability were not altered by the presence of laponite.

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010.
Committee Chair: Marder, Seth; Committee Co-Chair: Perry, Joseph; Committee Member: Dickson, Robert; Committee Member: El-Sayed, Mostafa; Committee Member: Riedo, Elisa. Part of the SMARTech Electronic Thesis and Dissertation Collection.

In the course of this thesis gold nanoparticle/polyelectrolyte multilayer structures were prepared, characterized, and investigated according to their static and ultrafast optical properties. Using the dip-coating or spin-coating layer-by-layer deposition method, gold-nanoparticle layers were embedded in a polyelectrolyte environment with high structural perfection. Typical structures exhibit four repetition units, each consisting of one gold-particle layer and ten double layers of polyelectrolyte (cationic+anionic polyelectrolyte). The structures were characterized by X-ray reflectivity measurements, which reveal Bragg peaks up to the seventh order, evidencing the high stratication of the particle layers. In the same measurements pronounced Kiessig fringes were observed, which indicate a low global roughness of the samples. Atomic force microscopy (AFM) images veried this low roughness, which results from the high smoothing capabilities of polyelectrolyte layers. This smoothing effect facilitates the fabrication of stratified nanoparticle/polyelectrolyte multilayer structures, which were nicely illustrated in a transmission electron microscopy image. The samples' optical properties were investigated by static spectroscopic measurements in the visible and UV range. The measurements revealed a frequency shift of the reflectance and of the plasmon absorption band, depending on the thickness of the polyelectrolyte layers that cover a nanoparticle layer. When the covering layer becomes thicker than the particle interaction range, the absorption spectrum becomes independent of the polymer thickness. However, the reflectance spectrum continues shifting to lower frequencies (even for large thicknesses). The range of plasmon interaction was determined to be in the order of the particle diameter for 10 nm, 20 nm, and 150 nm particles. The transient broadband complex dielectric function of a multilayer structure was determined experimentally by ultrafast pump-probe spectroscopy. This was achieved by simultaneous measurements of the changes in the reflectance and transmittance of the excited sample over a broad spectral range. The changes in the real and imaginary parts of the dielectric function were directly deduced from the measured data by using a recursive formalism based on the Fresnel equations. This method can be applied to a broad range of nanoparticle systems where experimental data on the transient dielectric response are rare. This complete experimental approach serves as a test ground for modeling the dielectric function of a nanoparticle compound structure upon laser excitation.
Im Rahmen dieser Arbeit wurden Gold-Nanopartikel/Polyelektrolyt Multischichtstrukturen hergestellt, strukturell charakterisiert und bezüglich ihrer optischen Eigenschaften sowohl statisch als auch zeitaufgelöst analysiert. Die Strukturen wurden mithilfe der Dip-coating oder der Spin-coating Methode hergestellt. Beide Methoden ermöglichen das Einbetten einzelner Partikellagen in eine Polyelektrolytumgebung. Typische Strukturen in dieser Arbeit bestehen aus vier Wiederholeinheiten, wobei jede aus einer Nanopartikelschicht und zehn Polyelektrolyt-Doppellagen (kationisches und anionisches Polyelektrolyt) zusammengesetzt ist. Die Stratizierung der Gold-Nanopartikellagen wurde mittels Röntgenreflektometrie-Messungen im Kleinwinkelbereich nachgewiesen, welche Bragg Reflexionen bis zur siebten Ordnung aufzeigen. Das ausgeprägte Kiessig Interferenzmuster dieser Messungen weist zudem auf eine geringe globale Rauheit hin, die durch Oberflächenanalysen mit einem Rasterkraftmikroskop bestätigt werden konnte. Diese geringe Rauheit resultiert aus den glättenden Eigenschaften der Polyelektrolyte, die die Herstellung von Multilagensystemen mit mehreren Partikellagen erst ermöglichen. Die Aufnahme eines Transmissionselektronenmikroskops veranschaulicht eindrucksvoll die Anordnung der Partikel in einzelne Schichten. Durch photospektroskopische Messungen wurden die optischen Eigenschaften der Strukturen im UV- und sichtbaren Bereich untersucht. Beispielsweise wird eine Verschiebung und Verstärkung der Plasmonenresonanz beobachtet, wenn eine Goldnanopartikellage mit transparenten Polyelektrolyten beschichtet wird. Erst wenn die bedeckende Schicht dicker als die Reichweite der Plasmonen wird, bleibt die Absorption konstant. Die spektrale Reflektivität jedoch ändert sich auch mit jeder weiteren adsorbierten Polyelektrolytschicht. Die Reichweite der Plasmonenresonanz konnte auf diese Art für Partikel der Größe 10 nm, 20 nm und 150 nm bestimmt werden. Die Ergebnisse wurden im Kontext einer Effektiven Mediums Theorie diskutiert. Die komplexe dielektrische Funktion einer Multilagenstruktur wurde zeitabhängig nach Laserpulsanregung für einen breiten spektralen Bereich bestimmt. Dazu wurden zuerst die Änderungen der Reflektivität und Transmittivität simultan mittels der Pump-Probe (Anrege-Abtast) Spektroskopie gemessen. Anschließend wurden aus diesen Daten, mithilfe eines Formalismus, der auf den Fresnelschen Formeln basiert, die Änderungen im Real- und Imaginärteil der dielektrischen Funktion ermittelt. Diese Methode eignet sich zur Bestimmung der transienten dielektrischen Funktion einer Vielzahl von Nanopartikelsystemen. Der rein experimentelle Ansatz ermöglicht es, effektive Medien Theorien und Simulationen der dielektrischen Funktion nach Laserpulsanregung zu überprüfen.

The application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA) which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analysed using the change in the Gibbs free energy computed by Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The Gibbs free energy was highest for PAA coated CNPs by 250 kg/mole indicating the most stable coating. The free energy for PAA 100 kg/mole coated CNPs is 85% lower than the PAA250 coated CNPs. This significant difference is caused by the strong adsorption of PAA100 on CNPs. Catalytic activity of PAA-CNPs is accessed by the catalase enzymatic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. Apart from PAA coating the catalase activity is also affected by the structure of the coating layer.
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering

Content: Nanoparticles showed a huge potential for new properties development in many economic sectors like electronics, medicine, textile, waste water treatment etc. The modification of surface functionality by using low concentrations of nanomaterials opens the possibility of lowering the ecological impact of chemical materials based on volatile organic compounds. The objectives of our research were related to the use of commercial nanoparticles based on Ag and TiO2 with average particle size of 8 nm for leather surface functionalization and the investigation of the cytotoxicological impact of nanoparticle concentrations on human skin cells. The practical implications of the approach consist of multifunctional leather surface development, leather durability and comfort increase by generating antimicrobial and self-cleaning properties. The relation between leather functionality and the cytotoxicity concentration limit of nanomaterials was the hypothesis of our research. The main procedures for leather surface covering followed the classical recipes based on surface spraying with film forming composites with nanoparticle content. The optimized technology was evaluated by leather surface analyses regarding the antimicrobial (SR EN ISO 20645) and self-cleaning properties under UV and visible light exposure as compared to leather surface covered without nanoparticles. The cytotoxicity tests were performed by incubation of keratinocytes (Human immortalized keratinocytes-HaCaT) with different concentrations of nanoparticles for 48 hours and measurement of cell viability by MTT (3-[4,5-dimethylthiazol- 2-yl]-2,5-diphenyltetrazolium bromide) assay protocol. Other tests were devoted to leather wearing simulation in order to estimate the potential transfer of nanoparticles on human skin and the health and safety impact. These simulations were based on rubbing test (SR EN ISO 11640) followed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) analyses and by leachability tests (SR EN ISO 4098) performed in artificial perspiration solution followed by inductively coupled plasma -mass spectrometry (ICP-MS) analyses, according to SR EN ISO 17294-2 and SR EN ISO 16171. The main conclusions of our research showed that it is possible to add multifunctional value to leather surface by using Ag and TiO2 nanoparticles with low impact on safety and health. Acknowledgements: The works were funded by UEFISCDI and MCI, project number PNIII_15/2015-2018 under the frame of SIINN, the ERA-NET for a Safe Implementation of Innovative Nanoscience and Nanotechnology program and respectively, PN 19 XX 05 01 project/2019 under Nucleus program TEX-PELVISION 2022 Take-Away: - antimicrobial and self-cleanning nanoparticles for leather surface finishing - Ag and TiO2 nanoparticle cytotoxicity tests for human skin cells - multifunctional surface properties with low cytotoxicological impact

The confluence of intriguing size and morphology dependent optical and chemical properties with versatile application in various fields, such as energetic and magnetic makes monometallic nonmaterial of high fundamental scientific interest. However, the challenge that needs to be addressed is to achieve their synthesis with a rational control on their dimensions, morphology and dispersion for the widespread applications of these materials. In addition to synthesis, achieving long-lasting stability of nonmaterial becomes imperative in order to realize their potential applications. Miniaturization in size of particles results in an increased surface to volume ratio, conducing especially reactive metal nanoparticals prone to oxidation. This thesis describes the synthesis of nearly monodiperse colloids of metallic and intermetallic nanoparticles using solvated metal atom dispersion method and digestive ripening facilitated interatomic diffusion process. Our aim is to understand the combinatiorial effects of nanosizing and stability on the functional properties of these nanomaterials. Towards this Direction, we investigated Co, A1 and Mg monometallic, and Au/Ag-In and Au-Sn intermetallic nanoparticle systems. Chapter 2 Describes the synthesis, detailed characterizations and magnetic properties of nearly monodisperse cobolt nanoparticles(<5nm) synthesized using a hydride synthetic protocol, solvated metal atom diserion method. The as-prepared cobalt nanoparticles in this size range exhibit intrinsic instability towards Oxidations. After 30 day of exposure to air, magnetic measurements showed drastic degration in saturation magnetization and complete conversion to antiferromagnetic cobalt oxide was confirmed. In order to achieve their stability, a heat treatment was applied to decompose the organic solvent and capping agent, resulting in carbonization of solvent/ligand around the surface of cobolt nano particles. Controlled and optimized annealing at different temperatures resulted in the formation of hexagonal closed packed (hcp) and fape-centered cubic (fcc) phases of metallic cobalt. Remarkably, the corresponding heat treated samples retained their rich magnetic behavior even after exposure to air for a duration of one year. Compared to un-annealed samples, magnetization values increased two-fold and the corecivity of nanoparticles exhibited strong dependence on the phase transformation of cobolt. Chapter 3 Deal with an exploratory study of the synthesis, characterization, and stabilization of nanometer-sized enegetic material, aluminum. Highly monodisperse colloidal aluminum nanoparticles (3.1‡ 0.6 mm) were prepared by using hexadecy amine (HAD) as the capping agent tetrahydrofurma as a coordinating solvent in the SMAD method. Since such small particles are highly prone to oxidation, a support materials is required for their stabilization. Stability has been achived by carbonization of the capping agent on the surface of A1 nanoparticles by carrying out thermal treatment of A1-HAD nanoparticles at a modest temperature. Presence of corbon was confirmed using Raman spectroscopy and TEM measurements evidencing that annealed A1 nanoparticles are encapsulated in a corbon matrix. The exhibition of robust stability was established using thermal analysis (TGA/DTA) wherein, oxidation of aluminum in air did not occur upto 500 0C. Indirectly, the successful passivation was further exploited in the synthesis and characterization of small sized monodisperse magnesium nanoparticles. The resulting samples were hybrided and nanosized MgH2 released hydrogen at much lower temperature than that of the bulk MgH2 (573 K). The observed hydrogen release was only partially reversible. This partial reversibility could be attributed to the coalescence of small sized Mg nanoparticles upon subsequent charging/discharging hydrogen cycles. In the next step, we exploed the intermetallic systes which are composed of more than one metallic species. Chapter 4 describes the synthesis and characterization of small sized, monodisperse (<10 nm) colloidal AuIn2 and Ag3In intermetallic nanoparticles. The formation of intermetallic nanoparticles could be explained by invoking digestive ripening facilitated atomic diffusion of Au/Ag and In nanoparticles followed simultaneously by their growth in te solution. The course of the reaction was followed using optical spectroscopy where the changes in UV-visible absorption band were correlated to the formation of AuIn/Ag3In intermetallic. Structural characterization, Performed using powder X-ray diffraction, brought out the formation of phase pure AuIn2 and Ag3In intermetallic compounds. Digestive ripening effects were clearly observed using transmission electron microscopy which showed the transformation of polydisperse physical mixture colloid of nanometallic species to uniform sized intermetallic nanoparticles. By invoking the phenomenon of interatomic diffusion at nanoscale favored by feasible thermodynamics ( G being negative) we were successful inrealizing the formation of these intermetallic nanoparticles. Optimization of temperature at which digestive ripening was performed, turned out to be a crucial factor in the successful synthesis of phase pure intermetallic nanoparticles. These promising results inspired us to study further the preparation of Au-Sn intermetallic system which is described in Chapter 5. The potential of such an unprecedented approach has been exploited in the synthesis of homogeneous intermetallic nanaocrystals of Au5Sn and AuSn. The two monometallic collids (Au and Sn), mixed in a stoichiometric amount were subjected to digestive ripening process. 1:1 stichiometry always led to the formation of eutectic mixture (Au5Sn and AUSn), The stoichiometry of monometallic nanocrystals. Therefore, by taking an extra equivalent of Au and Sn in two different experiments, phase pure Au5Sn and AuSn intermatillic nanocrsytals were obtained, respectively. This is the first observation that has been reported regarding the phase pure synthesis if Au5Sn intermetallic nanocrystals using solution based approach. Formation of different phases was established by structural characterization which elicited srystalline nature of the samples. A combination of TEM, HRTEM, and STEM-EDS mapping techniques employed here, brought and tailored phase. In conclusion, the careful selection of solvent, stoichiometry and growth directing agents is an important prerequisite for realizing distinct phases of Au-Sn system with a controlled morphology.

The confluence of intriguing size and morphology dependent optical and chemical properties with versatile application in various fields, such as energetic and magnetic makes monometallic nonmaterial of high fundamental scientific interest. However, the challenge that needs to be addressed is to achieve their synthesis with a rational control on their dimensions, morphology and dispersion for the widespread applications of these materials. In addition to synthesis, achieving long-lasting stability of nonmaterial becomes imperative in order to realize their potential applications. Miniaturization in size of particles results in an increased surface to volume ratio, conducing especially reactive metal nanoparticals prone to oxidation. This thesis describes the synthesis of nearly monodiperse colloids of metallic and intermetallic nanoparticles using solvated metal atom dispersion method and digestive ripening facilitated interatomic diffusion process. Our aim is to understand the combinatiorial effects of nanosizing and stability on the functional properties of these nanomaterials. Towards this Direction, we investigated Co, A1 and Mg monometallic, and Au/Ag-In and Au-Sn intermetallic nanoparticle systems. Chapter 2 Describes the synthesis, detailed characterizations and magnetic properties of nearly monodisperse cobolt nanoparticles(<5nm) synthesized using a hydride synthetic protocol, solvated metal atom diserion method. The as-prepared cobalt nanoparticles in this size range exhibit intrinsic instability towards Oxidations. After 30 day of exposure to air, magnetic measurements showed drastic degration in saturation magnetization and complete conversion to antiferromagnetic cobalt oxide was confirmed. In order to achieve their stability, a heat treatment was applied to decompose the organic solvent and capping agent, resulting in carbonization of solvent/ligand around the surface of cobolt nano particles. Controlled and optimized annealing at different temperatures resulted in the formation of hexagonal closed packed (hcp) and fape-centered cubic (fcc) phases of metallic cobalt. Remarkably, the corresponding heat treated samples retained their rich magnetic behavior even after exposure to air for a duration of one year. Compared to un-annealed samples, magnetization values increased two-fold and the corecivity of nanoparticles exhibited strong dependence on the phase transformation of cobolt. Chapter 3 Deal with an exploratory study of the synthesis, characterization, and stabilization of nanometer-sized enegetic material, aluminum. Highly monodisperse colloidal aluminum nanoparticles (3.1‡ 0.6 mm) were prepared by using hexadecy amine (HAD) as the capping agent tetrahydrofurma as a coordinating solvent in the SMAD method. Since such small particles are highly prone to oxidation, a support materials is required for their stabilization. Stability has been achived by carbonization of the capping agent on the surface of A1 nanoparticles by carrying out thermal treatment of A1-HAD nanoparticles at a modest temperature. Presence of corbon was confirmed using Raman spectroscopy and TEM measurements evidencing that annealed A1 nanoparticles are encapsulated in a corbon matrix. The exhibition of robust stability was established using thermal analysis (TGA/DTA) wherein, oxidation of aluminum in air did not occur upto 500 0C. Indirectly, the successful passivation was further exploited in the synthesis and characterization of small sized monodisperse magnesium nanoparticles. The resulting samples were hybrided and nanosized MgH2 released hydrogen at much lower temperature than that of the bulk MgH2 (573 K). The observed hydrogen release was only partially reversible. This partial reversibility could be attributed to the coalescence of small sized Mg nanoparticles upon subsequent charging/discharging hydrogen cycles. In the next step, we exploed the intermetallic systes which are composed of more than one metallic species. Chapter 4 describes the synthesis and characterization of small sized, monodisperse (<10 nm) colloidal AuIn2 and Ag3In intermetallic nanoparticles. The formation of intermetallic nanoparticles could be explained by invoking digestive ripening facilitated atomic diffusion of Au/Ag and In nanoparticles followed simultaneously by their growth in te solution. The course of the reaction was followed using optical spectroscopy where the changes in UV-visible absorption band were correlated to the formation of AuIn/Ag3In intermetallic. Structural characterization, Performed using powder X-ray diffraction, brought out the formation of phase pure AuIn2 and Ag3In intermetallic compounds. Digestive ripening effects were clearly observed using transmission electron microscopy which showed the transformation of polydisperse physical mixture colloid of nanometallic species to uniform sized intermetallic nanoparticles. By invoking the phenomenon of interatomic diffusion at nanoscale favored by feasible thermodynamics ( G being negative) we were successful inrealizing the formation of these intermetallic nanoparticles. Optimization of temperature at which digestive ripening was performed, turned out to be a crucial factor in the successful synthesis of phase pure intermetallic nanoparticles. These promising results inspired us to study further the preparation of Au-Sn intermetallic system which is described in Chapter 5. The potential of such an unprecedented approach has been exploited in the synthesis of homogeneous intermetallic nanaocrystals of Au5Sn and AuSn. The two monometallic collids (Au and Sn), mixed in a stoichiometric amount were subjected to digestive ripening process. 1:1 stichiometry always led to the formation of eutectic mixture (Au5Sn and AUSn), The stoichiometry of monometallic nanocrystals. Therefore, by taking an extra equivalent of Au and Sn in two different experiments, phase pure Au5Sn and AuSn intermatillic nanocrsytals were obtained, respectively. This is the first observation that has been reported regarding the phase pure synthesis if Au5Sn intermetallic nanocrystals using solution based approach. Formation of different phases was established by structural characterization which elicited srystalline nature of the samples. A combination of TEM, HRTEM, and STEM-EDS mapping techniques employed here, brought and tailored phase. In conclusion, the careful selection of solvent, stoichiometry and growth directing agents is an important prerequisite for realizing distinct phases of Au-Sn system with a controlled morphology.

The main objective of this research was to better understand the formation, stability and properties of emulsions having lipid nanoparticles with tunable functional properties by controlling the composition and structure of the biopolymer interface, in order to develop better food-grade delivery systems. Initially, the influence of environmental stresses (pH, heating and salts) on the physicochemical properties of cationic lactoferrin (LF)-stabilized oil-in-water emulsions was investigated. At ambient temperature, the emulsions were found to be stable at all times except when pH was close to pI. When LF-coated droplets were heated in distilled water, and then their pH was adjusted in the range 2 to 9, they were highly unstable to aggregation at pH 7 and 8. These results have important implications for the formulation and production of emulsion-based products using lactoferrin as an emulsifier. Next, we studied the properties and stability of multilayer emulsions formed using the primary emulsifier lactoferrin and secondary polysaccharides like low methoxyl pectin (LMP), high methoxyl pectin (HMP) and alginate. At neutral pH, electrostatic attractions occurred between the anionic groups on the polysaccharide molecules and the cationic patches on the protein surfaces. In the absence of polysaccharide, the LF-coated droplets were highly unstable to aggregation when heated above about 60 ºC at pH 7, presumably because thermal denaturation of the adsorbed proteins increased droplet attraction. Changes in the physicochemical properties and digestibility of both the primary LF and the secondary LF-polysaccharide emulsions, under simulated gastrointestinal conditions were monitored. The presence of a dietary fiber coating around the initial lipid droplets had little influence on the total extent of lipid digestion in simulated intestinal fluid (SIF), but LF-alginate emulsions had a slower initial digestion rate than the other emulsions. These results suggest that the dietary fiber coatings may become detached in the small intestine, or that they were permeable to digestive enzymes. Pepsin was found to have little influence on the physical stability or digestibility of the emulsions. Next, we fabricated emulsions with oil droplets coated by sequential electrostatic deposition of cationic LF and anionic β-lactoglobulin (BLG) at pH 6.5: LF, LF-BLG, LF-BLG-LF, and LF-BLG-LF-BLG. Changes in the physicochemical properties of these systems were characterized when they were exposed to environmental stresses and simulated small intestine conditions. LF-coated droplets were stable throughout the entire pH range which was attributed to strong steric repulsion. All the nanolaminated droplets were unstable to aggregation at pH 5, which is between the isoelectric points of BLG and LF. Finally, a "premix" approach was utilized to fabricate interfacial coatings around the lipid droplets, instead of the LbL approach. This method involved mixing BLG and LF prior to emulsion formation and the influence of environmental stresses on the properties of these emulsions was examined. Droplets coated by BLG were unstable to aggregation near their isoelectric point (pH ≈ 5), whereas those coated by LF were stable across the whole pH range. The stability of emulsions to pH induced aggregation improved as the ratio of LF-to-BLG in the mixed systems was increased. Lipid droplets coated by either LF or BLG were unstable to aggregation at high salt concentrations (500 mM NaCl, pH 6.5), but those stabilized by mixed protein coatings (LF and BLG) were stable, which was attributed to an increase in interfacial thickness and steric repulsion. Droplets coated by BLG were stable to droplet aggregation after thermal treatment (30 to 90 oC, 0 mM, NaCl pH 7), whereas those coated by LF were highly unstable when heated above their thermal denaturation temperature. The thermal stability of the droplets decreased as the amount of LF in the mixed systems increased. (Abstract shortened by UMI.)

碩士
國立中山大學
機械與機電工程學系研究所
98
The structural and electronic properties of small tungsten nanoparticles Wn (n=2-16) were investigated by density functional theory (DFT) calculation. For the W10 nanoparticle, ten lowest-energy structures were first obtained by basin-hopping method (BH) and ten by big-bang method (BB) with the tight-binding many-body potential for bulk tungsten material. These fifty structures were further optimized by the DFT calculation in order to find the better parameters of tight-binding potential adquately for W nanoparticles. With these modified parameters of tight-binding potentials, several lowest-energy W nanoparticles of different sizes can be obtained by BH and BB methods and then further refined by DFT calculation. According to the values of binding energy and second-order energy difference, it reveals that the structure W12 has a relatively higher stability than those of other sizes. The vertical ionization potential (VIP), adiabatic electron affinity (AEA) and HOMO-LUMO Gap are also discussed for W nanoparticles of different sizes.

The modification of surfaces with thin films is widely used to tailor physical and chemical properties of surfaces. This approach can provide "smart" surfaces with desired tunable properties. Polymer brushes represent a class of thin films, where the polymer chains are chemically end-grafted to the substrate. The chain functionality can be tailored by chemical composition, which allows the brushes to respond to external stimuli. In addition, polymer brushes may sterically stabilize colloids. Thus, polymer brushes are suitable candidates as a matrix for the incorporation of inorganic nanoparticles, like gold nanoparticles (AuNPs). AuNPs induce optical properties due to their surface plasmon resonance (SPR), which results in smart nanocomposite materials with tunable optical properties for the application as colorimetric sensors. The ability to control the particle amount and distribution within a brush matrix has a strong impact on fabrication of colorimetric sensors with optical properties on demand. In order to achieve brush/AuNP composites with desired properties, the thesis focuses on the impact of electrostatic interaction and hydrogen bonding on the formation of brush/AuNP composite materials. Here, pH-sensitive AuNPs are embedded into strong cationic and non-ionic polymer brushes. The electrostatic interactions and hydrogen bondings are tuned by changing the surface charge of the AuNPs through variations of pH value, while the charges of the brushes are not affected. The first part of the present thesis presents the assembly of pH-sensitive AuNPs into cationic polyelectrolyte brushes. In particular, the synergistic use of different characterization techniques clarify directly and indirectly effects of the electrostatic interaction on the structure, morphology and sensitivity of cationic brush/AuNP composites. The second part discusses the influence of using a non-ionic polymer brush on the assembly of pH-sensitive AuNPs. It is shown, that the nature of polymer brush has a crucial impact on the stabilization of incorporated AuNPs. This work demonstrates a novel approach to incorporate negatively charged AuNPs into non-ionic polymer brushes by using an electric field. Finally, the quality of brush/AuNP composites was experimental evaluated in terms of the long-term stability for the future prospect as colorimetric sensors. The thesis presents a fundamental understanding of smart coatings, where the particle-particle interaction as well as particle-brush interaction can be simply controlled by variation in pH value and governs their structure and responsive behavior.

Research Doctorate - Doctor of Philosophy (PhD)
The absorption cross-section over the optical range of frequencies of gold and silver clusters of up to 171 atoms was calculated using time-dependent density functional theory. Calculations were performed using the package Octopus and used the explicit time propagation method. The wavefunctions were calculated over a real-space grid and exchange-correlation interactions were including using the local density approximation. Structures were cleaved from a bulk crystal and included high-symmetry structures as well as structures with lower levels of symmetry. The evolution of the absorption spectra over cluster size was investigated and several trends were identified. As cluster size increases the absorption spectra becomes smoother. For gold clusters with more than approximately 70 atoms, the absorption spectra have several common features, including an absorption peak at around 2.5-3.0 eV, commonly attributed to a plasmonic oscillation. Absorption spectra were compared to past calculations and experimental measurements where available. For gold clusters above approximately 150 atoms, the calculated absorption spectra are in reasonable agreement with Mie theory calculations and experimental measurements. The effect of different calculation methods and approximations on the calculated absorption cross-section was also identified. The inclusion of spin-polarisation and the use of an exchange-correlation potential using the generalised gradient approximation had minor impact on the calculated absorption spectra. A new method of analysing the nature of peaks in the absorption spectra was also investigated. This method entailed exciting the system at a single frequency, and analysing the evolution of the electron density over time. This initial investigation indicated a difference in the evolution of the system when it was oscillated at a frequency corresponding to a plasmonic response as compared to a frequency corresponding to an electron hole excitation. This possibly indicates a method for investigating the nature of a plasmonic response in clusters of this size. This thesis demonstrates that with current computing power the optical absorption spectra of metallic clusters can be calculated using time-dependent density functional theory over a continuous range of cluster sizes from several atoms up almost to the point at which classical calculations become accurate. It identifies what calculation parameters are important to the optical absorption spectra for future calculations to agree with classical calculations as more computing power becomes available.

In an effort to develop broadly applicable photoswitchable catalysts, we have reported a method for modulating N-heterocyclic carbene (NHC) donicity using light by incorporating a photochromic diarylethene (DAE) into the backbone of a NHC scaffold. UV irradiation of 4,5-dithienylimidazolone or an analogous NHC-Ir(CO)₂Cl complex effected a photocyclization between the two thiophene rings, which led to a change in the electron donating ability of the NHC scaffold. Subsequent exposure to visible light reversed the photocyclization reaction. The concept of photo-modulating NHC donicity in this manner enabled photoswitchable NHC organocatalysis. The catalytic activity of a DAE-annulated imidazolium pre-catalyst in transesterification and amidation reactions was successfully switched between the active and nearly inactive states ([kappa]vis/[kappa]UV = 100) upon alternate UV ([lambda]irr = 313 nm) or visible ([lambda]irr > 500 nm) irradiation. The photoswitchable NHC organocatalysis was later extended to facilitating ring-opening polymerizations of cyclic esters, the rates of which were controlled via external light stimuli. Additionally, a photochromic dithienylethene-annulated N-heterocyclic carbene (NHC)-Rh(I) complex was synthesized and enabled photoswitching of the catalytic activity in series of hydroboration reactions. All of the examples demonstrate extremely rare instances of photomodulating a catalyst's activity by tuning its electronic properties. Furthermore, by taking advantage of the versatility of NHCs in both organo- and organometallic catalysis, we have developed novel photoswitchable catalysts for a variety of applicable transformations. Nanoparticles that can be transported in subsurface reservoirs at high salinities and temperatures are expected to have a major impact on enhanced oil recovery and electromagnetic imaging. We have developed an approach that will facilitate nanopaticle transport through porous media at high salinity by adsorbing or grafting rationally designed co-polymers on platform nanoparticles. Notably, co-polymers of acrylic acid with either 2-acrylamido-2-methylpropanesulfonate or styrenesulfonate have been electrostatically adsorbed or covalently grafted onto iron oxide nanoclusters. The presence of sulfonate groups on the iron oxide surface enabled long-term colloidal stability of the particles in extremely concentrated brine (8% wt. NaCl + 2% wt. CaCl₂) at elevated temperatures (90 °C) and minimized their adsorption on model mineral surfaces.
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The optical properties of plasmon resonant metallic nanoparticles are of great interest because of their ability both to control optical fields on the nanometer scale and to function as sensitive indicators of their local environment. I investigate the relationship between the dielectric function of a metal and the optical properties of the constituent metallic nanoparticle. Using a Drude shell - silica core nanoshell geometry, I examine how systematic changes in the parameters of the Drude dielectric function affect the near and far field properties of the nanoparticle. The nanoshell geometry allows separation of intrinsic properties and extrinsic phase retardation, or finite size, effects.

Dielectric oxides are an important class of materials, which are widely used in modern electronic and optoelectronic device applications. Ferroelectrics are the non-linear dielectrics, which possess piezoelectric, pyroelectric, and ferroelectric properties. Ferroelectric ceramic oxides are extensively utilized in various devices such as piezoelectric sensors, actuators, IR detectors, capacitors, energy storage, energy harvesting, and memory devices due to their outstanding physical properties. Among the different structural families, ferroelectric oxides belonging to the perovskite structure are widely used due to the possibility of tuning the physical properties as per the requirement of device applications. In order to further enhance the electromechanical, dielectric and ferroelectric properties, the fabrication of solid solutions with different types of perovskites are one of the suitable approaches. Around the morphotropic phase boundary (MPB) compositions of the ferroelectric solid solutions, anomalous enhancement of dielectric permittivity, polarization, electromechanical and piezoelectric properties are observed. In view of the processing and environmental issues pertaining to leadbased ferroelectric materials, investigations on lead-free ferroelectrics are carried out intensively in recent years. The 1st part of this work is mainly focused on the synthesis and characterization of high quality lead free ferroelectric ceramic oxides having general formula: (1-x) Na0.5Bi0.5TiO3–x BaTiO3 (NBT-BT) solid solutions (x = 0.00, 0.02, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.10). Among the available lead free ferroelectric ceramics, the A-site distorted perovskite (Na0.5Bi0.5)TiO3 (NBT) system has drawn immense attention due to their excellent dielectric, and ferroelectric properties. However, it has some limitations such as (i) high coercive field, (ii) high conductivity, (iii) high dielectric loss and (iv) high leakage current, which is against the use of this system in various device applications. In order to overcome these limitations, fabrication of solid solutions of NBT with BaTiO3 (BT) system has been studied. The NBT-BT ceramics are prepared by sol–gel auto combustion method followed by the sintering using microwave sintering technique. Structural, vibrational, dielectric, ferroelectric, and electrical properties of NBT-BT solid-solution are investigated using a wide variety of experimental techniques. The formation of single phase material with perovskite structure is confirmed from the X ray diffraction (XRD) patterns. A compositional driven structural phase transition from R3c (x = 0.0 to 0.05) to P4mm (x = 0.08 to 0.10) through an intermediate co-existence of R3c + P4mm (x = 0.06 and 0.07) is observed from X-ray Rietveld refinement and Raman spectroscopic studies. Existence of MPB composition has been observed in (1-x) Na0.5Bi0.5TiO3–x BaTiO3 solid solutions at x = 0.06. The same observation is also clearly seen in Raman spectroscopic studies. The scanning electron micrographs confirmed the presence of grains and grain boundaries with dense microstructure. It has been found that the grain size decreases with increasing of BaTiO3 (BT) concentration. The ferroelectric property has been studied by measuring P-E hysteresis loop after electrical poling and observed enhanced and welldeveloped ferroelectric loops after poling the ceramic samples. The highest polarization (2Pr O is observed for x = 0.06 sample. This enhancement of the ferroelectric properties could be resulted due to the presence of the MPB, i.e. the presence of both the rhombohedral and tetragonal phases. The temperature variation of dielectric properties shows two types of phase transitions such as (i) Relaxor ferroelectric to ferroelectric (TFR) and (ii) ferroelectric to paraelectric (FE-PE) phase transition (Tm or TC), for all compositions. It has been observed that the value of Tm is decreased with the increasing x, whereas there is a decrease in value of TFR with increase in composition up to x = 0.06 and thereafter it increases again. On the other hand, the value of dielectric permittivity at Tm (εrmax) increases with an increase in the composition up to x = 0.06 but with further increasing x, it decreases. The observed maximum value of dielectric permittivity at Tm and a minimum value of TFR for x = 0.06 may be due to the existence of MPB. Complex impedance, complex electrical modulus formalism, and frequency dependent ac conductivity analysis have also been carried out to study the relaxation and conduction mechanism. The presence of grain- and grain boundary contribution to impedance spectra in NBT–BT ceramics are analyzed using complex impedance plot (Nyquist plot) in association with complex modulus plot. The experimental data of these materials are fitted using suitable equivalent circuit to explain the electrical response of the materials. The frequency dependent of ac conductivity of these materials fits well with the double power law. The demand for miniaturized, flexible and light weight devices, leads to the development of flexible dielectric materials. There are two types of dielectric materials namely ceramics and polymers are widely used for storing the capacitive energy in capacitor. In view of this, ferroelectric polymer ceramic composites are one of the important R & D activities in the field of materials science. The polymer matrix in the polymer composites has the functionalities such as flexibility, easy processing, low cost and exhibit high breakdown strength. However, polymers are the materials having low dielectric permittivity. On the other hand, ferroelectric ceramic oxides have high dielectric permittivity but low breakdown strength. Therefore, the fabrication of ceramic-polymer composites can be a suitable solution for the problems associated with the ceramics and polymers, when considered separately for the energy storage. Solution-casting technique is used to prepare the free standing and flexible ferroelectric ceramic- polymer composite having general formula PVDF (Polyvinylidene fluoride) + ϕ wt.% of 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 (BNBT) (ϕ = 0, 5, 10, 15, 20, 25, 30, 35, 40 and 50) with 0-3 connectivity. This MPB composition BNBT has been chosen as filler as it possesses high dielectric permittivity and maximum polarization in the entire BNBT series. The semicrystalline nature and formation of composite due to the addition of BNBT filler to PVDF is confirmed from XRD analysis. The surface morphology of the prepared samples is studied using Field Emission Scanning Electron Microscope (FE-SEM), which shows the presence of spherulite and homogeneous distribution of ceramic filler particles in PVDF confirming the semicrystalline nature of the samples. In the polymeric chain of PVDF, systematic packing of parallel dipoles of fluorine atoms on one side yields higher electronegativity and hydrogen atoms on the other side (less electronegativity as compared to fluorine) with carbon as a backbone results in polar β-phase. FTIR and XRD results suggest that the fraction of the electro active β-phase increases with increase in filler concentrations and peaked for 35 wt.% of the ceramic filler. The increase in the fraction of β-phase has been explained based on ion (negatively charged surface ion of the ferroelectric ceramic filler)-dipole (-CH2 dipole of the polymer matrix) interactions, as evidenced from FTIR spectra. It has been observed that dielectric permittivity keep on increasing with addition of ceramic filler up to 35 wt.%. However, above 35 wt.% a decrease in the dielectric permittivity value has been observed for all the frequencies. Swift Heavy Ion (SHI) irradiation is one of the most effective, powerful and emerging techniques for tailoring the physico-chemical properties of the material suitable for a particular application. The effect of Swift Heavy Li3+ ion beam (50 MeV) irradiation with different fluence (ranging from 1×1011 to 3.3×1013 ions/cm2) on the structural, morphological, vibrational, dielectric and ferroelectric properties of PVDF and PVDF + 35 wt.% BNBT (PVDF-BNBT) composite are studied. XRD patterns show an increase of β-phase and degree of crystallinity upon irradiation for the respective films. The scanning electron microscopic study showed a systematic increase in the spherulites size with irradiation. Dielectric permittivity and ferroelectric polarization of PVDF and PVDF-BNBT composite is increased with increase of fluence and the highest value is observed for the highest fluence. So the interaction of Li3+ ions with polymer composite leading to the enhancement β-phase, which plays the decisive role for the enhancement of the functional properties such as dielectric and ferroelectric properties