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1
Wang, Menghong. "Degradation of Photovoltaic Packaging Materials and Power Output of Photovoltaic Systems: Scaling up Materials Science with Data Science." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1595416965256375.
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Liu, Tong. "Construction of Supramolecular Structures by Mimicking Metallurgy." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron160370390740064.
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Shichen, Yu. "CHAIN ENTANGLEMENTS EFFECTS IN NASCENT ULTRA-HIGH MOLECULAR WEIGHT POLYPROPYLENE SYNTHESIZED BY ZIEGLER – NATTA MULTIPLE-SITES AND METALLOCENE SINGLE-SITE CATALYSTS." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1620286973657457.
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Zhang, Ci. "Humidity Response of Capture Silk and Its Effect on Adhesion." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428335464.
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Dong, Hui. "Devulcanization Of Waste EPDM Rubber And Manufacturing Of Polypropylene (Pp)/ Waste EPDM Thermoplastic Elastomers Using Ultrasonically Aided Extrusion." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430683095.
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Zhang, Chi. "Wetting on Lubricant Infused Polyeletrolyte Multilayer Surfaces." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1435735900.
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Peng, Peng. "PREPARATION AND CHARACTERIZATION OF POLYMER/FERROELECTRIC CERAMIC PARTICLE COMPOSITES FOR ELECTROACTIVE ACTUATION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1443539252.
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Feng, Jiawei. "Compatibility and Shape Memory Effect Study of Maleated Ethylene Propylene Copolymer(MAn-g-EPM)/Fatty Acid Blends." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1500514544100023.
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Chen, Peiru. "Surface functionalized TPU for antifouling catheter application." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525170686769959.
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Smith, Scott M. "Resolving the Mechanistic Origins of Reinforcement in Filled Elastomers Using Molecular Simulation." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1531739330550906.
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HUANG, DA. "Molecular Insights Into the Deformation of Polymer Glasses Revealed by Real-time Birefringence Measurements." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1590418690531163.
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Johnson, Joseph Casey. "Peptidic Materials: Nature Inspired Mechanical Enhancement." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1403197488.
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Li, Bing Li Christopher Yuren. "Exploiting polymer single crystals to assemble and functionalize nanomaterials /." Philadelphia, Pa. : Drexel University, 2009. http://hdl.handle.net/1860/3182.
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Zheng, Jincai Cernansky N. P. Miller David L. "A study of homogeneous ignition and combustion processes in CI, SI, and HCCI engine systems /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/557.
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Badge, Ila. "Tuning Wettability And Adhesion Of Structured Surfaces." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1393716842.
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He, Tianda. "Electrospun Nanofibers and Their Applications in Transparent Electrodes." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396876037.
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Shams, Es-haghi Siamak. "Mechanics of Tough Chemically Cross-linked Hydrogels." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430411138.
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Lee, Jeongwoo. "Fabrication of polymer/metal oxide composites through polymerization-induced phase separation and characterization of their mechanical and electrochemical properties." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1446217264.
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Ge, Sirui. "The Entanglement-Disentanglement Transition (EDT) During Creep With Either Constant Or Oscillatory Stress In Highly-Entangled Polybutadiene Solution." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1459949733.
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Zhao, Wenhan ZHAO. "SMALL ANGLE X-RAY SCATTERING AND RHEOLOGY STUDIES OF POLYISOBUTYLENE WITH OLIGO(ß-ALANINE) GRAFTS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1528983070278315.
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Liu, Suqi. "Droplet-jet shape in electrospinning: real-time feedback control of nanofiber diameter." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1573221625942164.
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Rahner, Nils. "Inorganic polymers (geopolymers) as potential bioactive materials : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Master of Science in Chemistry /." ResearchArchive@Victoria e-thesis, 2009. http://researcharchive.vuw.ac.nz/handle/10063/952.
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Razgoniaev, Anton. "Design, synthesis, and characterization of photoresponsive materials usingcoordination bonds and other supramolecular interactions." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1510918007338796.
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Li, Lingyu Li Christopher Yuren. "Polymer crystallization enabled carbon nanotube functionalization: morphology, structure and applications /." Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1223.
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Tahhan, May. "Carbon nanotubes and conducting polymer composites." Intelligent Polymers Research Institute - Faculty of Science, 2004. http://ro.uow.edu.au/theses/407.
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A nanocomposite is defined as a material of more than one solid phase, where at least one dimension falls in the nanometer range. The combination of carbon nanotubes (CNT) and conducting polymers offers an attractive route for the production of novel compounds that can be used in a variety of application such as sensors, actuators, and molecular scale electronic devices. The ultimate goal of this work is to develop and investigate CNT composites that provide a structural functionality together with one or more other key functions. A variety of novel CNT dispersions were prepared using commercially available CNT systems such as Rice single-walled carbon nanotubes (RCNT), HiPco single-walled carbon nanotubes (HCNT), and Multi-walled carbon nanotube (MWCNT). This study explored the application of novel functional dispersing agents. Deoxyribose Nucleic Acid (DNA) a biological molecule, N- sopropylacrylamide 2-acrylamido-2-methyl-1-propanesulfonic acid (NIPPAm-AMPS) a polyelectrolyte, Didodecyldimethyl ammonium bromide (DDAB) a polymerizable compound, Poly(methoxyaniline-5-sulfonic acid) (PMAS) an inherently conducting polymer, and PVA an insulating polymer were some of the agents used to disperse the CNT. These dispersions were then evaluated in term of their stability and ability to effectively disperse the CNT. Solid-state CNT composites (mats) were then prepared by means of pressure filtration of the CNT/dispersant solutions. These mats were characterized using a variety of different techniques to determine their viability to be used as mechanical actuators or electrochemical devices. The characterization methods included cyclic voltammetry, conductivity, capacitance, atomic force microscopy, scanning electron microscopy, Young’s modulus, and actuation measurements. Abstract RCNT/conducting polymer composites were prepared by the electropolymerization of Pyrrole with a range of different dopant anions in the presence of different RCNT dispersions. In these composites, the RCNT were completely covered by the polymer, consequently the electrochemical responses of these composites were dominated by the electrochemistry of the polymers with the CNT functioning as a conductor element. Polypyrrole was also electropolymerized using functionalized multi-walled carbon nanotubes (FMWCNT) as dopant. Electropolymerization was carried out using galvanostatic and potentiostatic techniques on gold-coated Mylar and ITO-glass. It was determined that PPy/FMWCNT composites deposited on either electrode using potentiostatic deposition exhibited redox peaks. This redox behavior was not observed when the galvanostatic deposition was employed. HCNT/Polyaniline (PAn) composites were prepared by either casting a film from a solution of HCNT and PAn in 1,2-Dichlorobenzene, or by casting a film of PAn onto an existing HCNT mat. The latter exhibited the highest conductivity. The actuation behavior of these CNT composites was investigated and it was determined that the PAn component contributes to the actuation strain while the HCNT component contributes to Young’s modulus. The combination of the HCNT (with their mechanical properties) and PAn (with its actuator behavior) offers and attractive route not only to reinforce the polymer film but also to introduce new electronic properties based on morphological modifications or electronic interactions between the two components giving a robust blend of optimum properties. These results open the door for these composites to be used in a variety of applications that require a combination of the above characteristics such as mechanically reinforced actuator devices, robotics, optical fiber switches, prosthetic devices, and anti-vibration systems. In addition, PPy with a range of dopant anions was electrodeposited galvanostatically, potentiostatically, and potentiodynamically on the surface of four different carbon electrodes, RCNT mat (unannealed), RCNT mat (annealed), glassy carbon, and carbon foil. It was found that the method of electrodeposition was crucial to the electroactivity of the deposited polymers, particularly when deposited onto a RCNT mat due to the different interaction between the deposited polymer and the RCNT mat. Finally, HCNT/SDS, HCNT/PMAS, and HCNT/DNA fibers were prepared using the Particle Coagulating Spinning method (PCS). The annealing process resulted in a dramatic increase in conductivity of up to 2600 times higher compared to the unannealed fibers. However, the annealing process did not play any role in keeping the fibers together or modifying the alignment of the carbon nanotubes ropes within the fibers. The HCNT/DNA fibers, with their biocompatibility, high conductivity, and good mechanical properties can be used as artificial muscles, bioelectronic sensors, or even as platforms to support the growth of nerve cells. This thesis delineates the methods of successful production of solid sate CNT mats and fibers, utilizing traditional polymeric and more novel multi- functional dispersant materials. Thereby, providing a series of new framework for which future device structures can be fabricated.
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Hundt, Nadia Khanam. "Novel thiophene-containing semiconducting polymers for organic electronic applications /." 2009. http://proquest.umi.com/pqdweb?did=1952837921&sid=2&Fmt=2&clientId=10361&RQT=309&VName=PQD.
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Zerda, Adam S. "Molecular and nanoscale reinforcement of polymers." 2002. https://scholarworks.umass.edu/dissertations/AAI3068604.
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The reinforcement of polymers using additives of dimensions below one micrometer is presented: those acting at the molecular and nanometer scales. This thesis will describe new additives and morphologies exhibiting high levels of mechanical reinforcement. It is the focus of this work to chronicle the range of physical and material properties that are altered upon inclusion of these modifiers. Additionally, this thesis will establish how these physical-property changes affect the mechanical behavior of the resulting composite. In the area of molecular reinforcement, a new class of additive, the organophosphate, is shown here to enhance modulus and yield strength in epoxy polymers once cured. Initially, the effect on the physical and thermal properties of the polymer system is investigated as a function of additive molecular weight, solubility, and concentration. The altered properties include T g, density, thermal stability and initial epoxy viscosity. The mechanical properties of the modified epoxy are demonstrated to be a result of the physical changes made to the matrix polymer through the addition of the organophosphorous additive. By increasing the density of the polymer and reducing or eliminating sub-Tg relaxations, the modulus and yield strength of the polymer can be greatly enhanced. These property changes are investigated in a variety of epoxy polymer systems in order to elucidate the effects of both the additive and polymer chemical structure on final mechanical properties. Polymer modification using nanometer-scale additives and modifiers has been the focus of intense study recently. Heretofore, these studies have focused on the exfoliated, or delaminated, clay morphology to impart the property enhancements, effectively isolating the particulates within the matrix. This thesis focuses on polymer modification at the nanometer scale such that the added clays interact and positively change the composite fracture toughness. By introducing this clay-clay interaction, modulus and strength can be increased together with the toughness. Such a property combination is highly desirable, as most toughening agents reduce modulus and strength. Initially, the intercalated morphology is investigated in an epoxy system. Additionally, new routes to synthesizing intercalated morphologies of clay concentrations approaching 50% are developed.
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Su, Zhaohui. "Chemical modification of polymers and properties of functionalized polymers." 1997. https://scholarworks.umass.edu/dissertations/AAI9809403.
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The work presented in this thesis is divided into four chapters. Chapter I describes the control of the crystallization behavior of syndiotactic polystyrene (sPS) by chemical modification of sPS using sulfonation. In Chapter II, preparation of wood-ceramic composites through sol-gel processes is described. Chapter III describes the end-functionalization of poly(ethylene oxide)s (PEOs), and the interfacial properties of the functionalized PEOs. Finally, the distribution of chain conformation of PEO in the liquid state is discussed in Chapter IV. Direct sulfonation of highly stereoregular syndiotactic polystyrene (sPS) has been accomplished in chloroform. The degree of sulfonation can be effectively controlled. The crystallization behavior of sulfonated sPS is considerably different than the unmodified polymer. The crystallinity and the crystallization kinetics of sPS decrease with increasing extent of modification. Wood-ceramic composites were prepared by introducing a ceramic component into pine, a softwood, through sol-gel processes. Several ceramic precursors, including SiCl$\sb4$, Si(OCH$\sb3)\sb4$, and CH$\sb3$SiCl$\sb3$, were used. The ceramic content introduced into the wood structure can be controlled by varying the reaction time and the moisture content of wood. The modification of wood by CH$\sb3$SiCl$\sb3$ in supercritical CO$\sb2$ penetrated the entire wood structure, generating a macroscopically uniform distribution of the ceramic component in wood. Samples with one or both ends of monodisperse PEO functionalized with perfluorodecanoyl groups (PEO$\sp{\rm F}$ or PEO$\sp{\rm F2}$) were synthesized and blends of these end-capped PEOs with PEOs of the same molecular weight (M$\sb{\rm n}$$\sim$2000 - $\sim$16000) were prepared as cast films. Due to the lower surface energy of the fluorocarbon end groups, the modified PEOs preferentially adsorb to the free polymer surface. The surface concentration of the perfluoroalkyl end groups was measured by XPS which indicates that perfluoroalkyl chain ends adsorb to the polymer surface in a reasonably close-packed fashion (at all molecular weights) and leave a zone depleted of fluorine immediately beneath the highly fluorinated surface region. There is only a slight effect of molecular weight on surface fluorine content indicating a "stretched brush" conformation for the higher molecular weight samples. The adsorption of these polymers at the air-water interface was studied as well. The packing density and the orientation angle of the fluorinated chain end segregated at the interface were assessed by external reflectance IR. Isotropic Raman spectra of PEO in aqueous solution and in the melt were simulated by superposing calculated spectra resulting from a series of normal coordinate calculations performed for an ensemble of conformers, and compared with the corresponding experimental results. The conformational distribution for poly(ethylene oxide) in the molten state favors the tgg' conformer, and the aqueous solution of poly(ethylene oxide) contains mostly tgt conformers. The results for PEO were supported by measurements and computations made using 1,2-dimethoxyethane as a model.
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Rockford, Lee David. "Polymers on nanoperiodic, heterogeneous surfaces." 2001. https://scholarworks.umass.edu/dissertations/AAI3000338.
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Herein we establish a relationship between controlled nanoscale surface interactions and subsequent macromolecular ordering. Chemically heterogeneous striped surfaces of polar silicon oxide and non polar gold are generated over large areas, via glancing angle evaporation on facetted silicon substrates. The processing conditions required for generation of stripe widths comparable to the size of a polymer molecule are outlined. Substrates with 20–30 nm metal linewidths and 40–60 rim stripe periods are prepared. Spin and solution casting of incompatible polymer mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) on heterogeneous surfaces are found to generate films with unique, substrate directed morphologies dependant on the kinetics of the casting process. Spin cast films posses a surface adsorbed layer of blended composition due to rapid polymer adsorption from solution, while solution cast films phase separate at the substrate/polymer interface on a molecular level. Preferential adsorption of PS to the non polar gold stripes and PMMA to polar silicon oxide stripes is observed at the substrate beneath the macroscopically phase separated domains of the blend components. Preferential adsorption occurs over a large molecular weight range, with a molecular weight dependence on the morphology of the adsorbed polymer lines found. Solution cast films of the symmetric copolymer poly(styrene-block-methylmethacrylate), P(S-b-MMA), on heterogeneous surfaces show lamellar microdomain orientations perpendicular to the substrate plane, parallel to the striping. Commensurability of the block copolymer and substrate stripe periods is found to be essential for producing such a surface directed morphology. The commensurability window depends inversely on the degree of confinement of the morphology, with unconfined films requiring more stringent conditions for surface directed morphology reorientation. The distance over which the orientation of the microdomains persists in thick films is found to depend on the ordering kinetics, scaling with copolymer molecular weight. Confinement effects such as tension and compression and defects in the lateral long range orientation of surface directed lamellar morphologies are observed for slightly incommensurate morphologies, with the amount of strain and defect concentration found to increase with the loss of commensurability.
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Zhang, Huiqing. "Fire -safe polymers and polymer composites." 2003. https://scholarworks.umass.edu/dissertations/AAI3110571.
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The intrinsic relationships between polymer structure, composition and fire behavior have been explored to develop new fire-safe polymeric materials. Different experimental techniques, especially three milligram-scale methods—pyrolysis-combustion flow calorimetry (PCFC), simultaneous thermal analysis (STA) and pyrolysis GC/MS—have been combined to fully characterize the thermal decomposition and flammability of polymers and polymer composites. Thermal stability, mass loss rate, char yield and properties of decomposition volatiles were found to be the most important parameters in determining polymer flammability. Most polymers decompose by either an unzipping or a random chain scission mechanism with an endothermic decomposition of 100–900 J/g. Aromatic or heteroaromatic rings, conjugated double or triple bonds and heteroatoms such as halogens, N, O, S, P and Si are the basic structural units for fire-resistant polymers. The flammability of polymers can also be successfully estimated by combining pyrolysis GC/MS results or chemical structures with TGA results. The thermal decomposition and flammability of two groups of inherently fire-resistant polymers—poly(hydroxyamide) (PHA) and its derivatives, and bisphenol C (BPC II) polyarylates—have been systematically studied. PHA and most of its derivatives have extremely low heat release rates and very high char yields upon combustion. PHA and its halogen derivatives can completely cyclize into quasi-polybenzoxazole (PBO) structures at low temperatures. However, the methoxy and phosphate derivatives show a very different behavior during decomposition and combustion. Molecular modeling shows that the formation of an enol intermediate is the rate-determining step in the thermal cyclization of PHA. BPC II-polyarylate is another extremely flame-resistant polymer. It can be used as an efficient flame-retardant agent in copolymers and blends. From PCFC results, the total heat of combustion of these copolymers or blends changes linearly with composition, but the change of maximum heat release rates also depends on the chemical structure of the components. The flammability of various polymers and polymer composites measured by PCFC, cone calorimeter ASTM E1354 and Ohio State University (OSU) calorimeter ASTM E906 were also compared. For pure polymers, there is a relatively good correlation between different methods. However, for polymer composites with inert fillers or flame-retardant additives, OSU and cone calorimetries are more suitable evaluation methods.
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Chen, Wei. "Polymer surface modification: Chemical surface modification, layer-by-layer adsorption, and surface reconstruction." 1997. https://scholarworks.umass.edu/dissertations/AAI9809316.
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The three projects, chemical modification (Chapter 1), layer-by-layer deposition (Chapter 2), and surface reconstruction (Chapter 3), that constitute this Ph.D. thesis are closely related in their overall objectives: using polymer surface modification to manipulate microscopic surface structures and control macroscopic properties. Alcohol functionality can be introduced to the surface of poly(ethylene terephthalate) (PET) using either reduction or glycolysis; both of which cleave the PET chain. Both of these modified surfaces (PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G})$ and hydrolyzed PET (PET-OH/COOH) can be prepared using conditions that optimize surface functional group concentration, but minimize sample degradation. The surface alcohol density is higher on PET-OH$\rm\sp{G}$ than on PET-OH$\rm\sp{R}$ by a factor of $\sim$2. The concentration of alcohols on reduced surfaces is increased by solvent annealing of the PET film prior to reduction. Reactivities of PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G}$ samples were assessed and compared. Layer-by-layer deposition of polyelectrolytes (poly(allylamine hydrochloride)) and poly(sodium styrenesulfonate)) has been used to build up multilayer films on three organic polymer substrates: PET, PET-CO$\sb2\sp-$ and PET-NH$\sb3\sp+.$ XPS and contact angle data indicate that the layers are stratified and the wettability of the multilayer assemblies is largely controlled by the identity of the outermost polyelectrolyte layer. The layer thickness and the stoichiometry of the deposition process (ammonium ion:sulfonate ion ratio) are affected by the substrate surface chemistry and can be controlled by adjusting the ionic strength of the polyelectrolyte solutions. Peel tests indicate that the multilayer assemblies show good mechanical integrity. A perfluorohexylated-C$\sb{60}$ (fullerene) was prepared and its surface activity and mobility were studied as a function of bulk concentration, annealing temperature, and annealing time in a polymer matrix (polystyrene). Perfluorohexylated-C$\sb{60}$ is extremely surface-active in the polystyrene matrix and occupies 95%-85% of the outermost 10 A-40 A (XPS results), and renders a surface that is similar to a monolayer containing -CF$\sb3$ groups (hexadecane contact angle data). Surface reconstruction studies were carried out via either spin-casting or transferring a free standing polystyrene film over the composite materials (the surface-active agent and polystyrene). Both approaches show similar behavior of migration of perfluorohexylated-C$\sb{60}$ from the bulk to the surface.
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Gower, Laurie Anne. "The influence of polyaspartate additive on the growth and morphology of calcium carbonate crystals." 1997. https://scholarworks.umass.edu/dissertations/AAI9809341.
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The addition of low levels of polyaspartate to a supersaturated calcium carbonate (CaCO$\sb3$) solution leads to unusual morphologies in the inorganic phase. Spherulitic vaterite aggregates with helical protrusions, and distorted calcite crystals that contain spiral pits, have been produced. The helical particles are coated with an inorganic membrane that appears to be responsible for the helical twist. The polymer also causes deposition of thin CaCO$\sb3$ tablets and films on the glass substrate. Two distinct types of films are deposited; the first is a mosaic of calcite crystals, and the second is spherulitic vaterite. In situ observations of the crystallization reaction have determined that the thin-film morphology is a result of the phase separation of a hydrated CaCO$\sb3$/polymer liquid-precursor, whereby accumulation of isotropic droplets creates a coating on the substrate, and subsequent dehydration and crystallization yields birefringent CaCO$\sb3$ films. During the amorphous to crystalline transition, incremental growth steps lead to "transition bars" and sectored calcite tablets. This in vitro system was originally modeled after certain aspects of CaCO$\sb3$ biomineralization, in which the soluble proteins extracted from biominerals tend to have high levels of aspartic acid residues. Based on the similarities between features exhibited by the products of this system and those in biominerals, an argument has been presented to suggest that this polymer-induced liquid-precursor (PILP) process is involved in the morphogenesis of CaCO$\sb3$ biominerals. These features include the following: thin CaCO$\sb3$ tablets that grow laterally; tablets that express unstable crystallographic faces; non-faceted single crystals with curved surfaces; spatially-delineated single crystals; sectored calcite tablets; hollow-shell spheres; calcium carbonate cements; and magnesium-bearing calcites. This work has demonstrated that a means of morphological control can be accomplished through non-specific organic/inorganic interactions, whereby the polyelectrolyte transforms the solution crystallization to a solidification process. Not only are such findings of significance to the field of biomineralization, but a better understanding of the interactions between polymers and inorganic materials may be expected to lead to new strategies for crystal and particle engineering.
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Kim, Taehyung. "Polymer nanorods: Preparation, analysis, and chemical modification." 2007. https://scholarworks.umass.edu/dissertations/AAI3254958.
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The overall objectives of the projects which constitute this Ph.D. thesis are a preparation of two-component polymer nanorods using anodic alumina membranes as templates and an investigation of their structures as well as a possibility for a preparation of composite nanorods. Anodic alumina membranes with various pore size prepared by the anodization of aluminum in electrochemical cell are used as well as commercial membrane (Chapter 2). Diblock copolymer nanorods are prepared using these membranes and their microphase-separated structures inside the membrane pores are investigated (Chapter 3 and 4). Semicrystalline polymer nanorods are prepared using these membranes and their composites are prepared by polymerizing second monomer inside these nanorods (polymer/polymer composite nanorods) or depositing metal clusters inside these nanorods (polymer/metal composite nanorods) (Chapter 5). Microphase-separated structures of diblock copolymers inside the cylindrical membrane pores are affected by the relationship between the size of pores and the repeat period of the block copolymers (commensurability). Polystyrene- b-polybutadiene (PS-b-PBD) confined inside the membrane pores show novel structures that cannot be accessed by any other method, caused by the commensurability and large curvature of the templates. The interaction between each block of diblock copolymer and the alumina surface is another factor for the micro-phase separated structures of diblock copolymers inside alumina membrane pores. Surface modification of alumina membrane pores using octyltrimethoxysilane (OTMS) inverted the multi-barrel structure of symmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) and asymmetric PS-b-PMMA at large D/L 0, by changing the polarity of the templates. Asymmetric PS- b-PMMA at small D/L0 does not show this inversion. Poly(4-methyl-1-pentene) (PMP) nanorods are prepared using commercial alumina membranes. PMP/polynorbornene nanorods are prepared by polymerizing norbornene inside PMP nanorods using liquid CO2 as reaction medium. This also provides a way to observe the structures of these semicrystalline polymer nanorods. PMP/Pt nanorods are prepared by introducing Pt precursors, dimethyl(cyclooctadiene)platinum(II) (CODPtMe2), clusters using supercritical CO2 as a medium and reducing it with H2 to form Pt clusters inside PMP nanorods.
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Herrera-Alonso, Margarita. "Surface chemistry of poly(p-xylylene) and nylon." 2005. https://scholarworks.umass.edu/dissertations/AAI3163673.
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The interaction of a material with its surroundings occurs at the material-environment interface, therefore, the chemical and physical characteristics of the material's surface plays a fundamental role in determining its properties, such as its biocompatibility, adhesion, and wettability, and ultimately, its technological applicability. This dissertation discusses aspects of the chemical surface modification of two polymers, poly(p-xylylene) and nylon. Chapter 2 focuses on the synthesis and wet-chemistry surface modification of poly(p-xylylene) (PPX) thin films. A series of electrophilic aromatic substitutions were studied including chlorosulfonation, chloroamidomethylation, and Friedel-Crafts catalyzed reactions. It was found that the yields and surface selectivity of the reactions studied were highly dependent on the interaction of the polymer with the reaction medium. Chapter 3 describes the use of vapor deposition polymerization in template-assisted synthesis. Poly(p-xylylene) nanotubes were synthesized by template assisted methods using porous aluminum oxide membranes as the templating material. The pore diameter showed a linear dependence with respect to the deposition time. FESEM analysis showed that PPX was deposited along the pores of the membranes. Exposure of the membranes to a reactive solution resulted in chemical functionalization of the inner walls of the nanotubes, confirmed by XPS. Chapter 4 discusses the chemical reduction of nylon film surfaces by reaction with a borane-tetrahydrofuran complex. It was observed that, while the reaction occurs in high yields, its surface-confinement is highly dependent on the segmental mobility of the polymer. The amine-rich surfaces were further used as templates for the synthesis of composite films by electrostatic adsorption of polyanions. Chapter 5 deals with the synthesis of linear polyalkyleneimines of different hydrocarbon lengths by the surface-mediated reduction of nylons. These polyalkyleneimines were further used as compatibilizers for the melt intercalation of montmorillonite clays, modified and unmodified, with polypropylene. The polyamines were found to interact favorably with the clays, leading to intercalated and exfoliated systems. The determining factor in controlling the degree of dispersion of the clays, was the enthalpic interaction between the clay and the compatibilizer.
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Lavery, Kristopher A. "Pressure effects on entropically driven phase transitions in block copolymers." 2005. https://scholarworks.umass.edu/dissertations/AAI3193915.
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The binary polymer system of polystyrene and poly(n-pentyl methacrylate) was recently found to exhibit closed-loop type phase behavior. This is the first known example of a weakly interacting system exhibiting such a phase diagram. At atmospheric pressure the block copolymer displays both a lower disorder-to-order and upper-order-to-disorder transition, representing the lower and upper bounds of the closed-loop phase diagram. The application of hydrostatic pressure served to shrink the closed-loop, yielding pressure coefficients of the lower disorder-to-order and upper order-to-disorder transitions of 725°C/kbar and -725°C/kbar respectively. These pressure coefficients were consistent with those calculated from the Clausius-Clapeyron equation, using the experimentally determined ΔHdisorder and ΔV disorder for each transition. The χeff determined from small angle neutron scattering (SANS) was found to decrease, pass through a minimum, increase to a maximum, and then decrease with increasing temperature. Swelling the system with carbon dioxide served to promote an expansion of the closed-loop. This was due to the entropic nature of both transitions, with differential dilation of the copolymer domains resulting in dissimilar compressibilities of the blocks. In addition to influencing block copolymer phase behavior, carbon dioxide can have a profound impact on resulting morphological structure. A 42/58 PS-b-PnPMA diblock copolymer was found to exhibit lamellar morphology at ambient pressures. With the application of 2500 psi carbon dioxide the morphology shifted to hexagonally-packed cylinders due to preferential absorption into the PnPMA block. Furthermore, the influence of carbon dioxide sorption on the morphology of the PS/poly(n-alkyl methacrylate) block copolymer series was studied both in thin films and in the bulk.
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McNamara, Joseph E. "Monte Carlo, small angle light scattering, and dynamic light scattering studies of dilute polymer solutions." 2005. https://scholarworks.umass.edu/dissertations/AAI3193925.
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The adsorption of negatively charged polymer, negative/neutral block copolymer and a polyampholyte to patterned surfaces is investigated using off-lattice Monte Carlo simulations. The surface is decorated by stripe and checkerboard patterns of mixed charges. The polymer has periodic charge segments, which potentially match the periodicity of the surface pattern. Results show that the chain entropy of a flexible polymer disrupts and prevents full pattern recognition. Quantities such as average adsorption energy and the radii of gyration of the adsorbed polymer are calculated and found to be dictated by the size of the surface pattern and its correlation to the polymer charge density. We performed small angle light scattering on dilute-solution-grown polyethylene crystals grown from quenches in para-xylene. The quench depths ranged from 60 to 85°C for 0.05 wt.% and 0.1 wt.% linear-low-polydispersity polyethylenes. We found asymmetric scattering patterns for the lower temperature quenches to 65°C, and symmetric scattering patterns for the higher temperature quenches to 80°C. There is a smooth transition from asymmetric to symmetric scattering as we change the quench depth. The correlation lengths d=2π/qmax corresponding to the peaks of intensity versus q ranged from 15 to 30 μm. We find evidence that these length scales correspond to assemblies of single polyethylene crystals. Also, we have performed dynamic light scattering on solutions of sodium-poly(styrene-sulfonate) (NaPSS) and poly(ethylene-oxide) (PEO) in water with BaCl2. The fast mode ( Dfast) and slow mode (Dslow) diffusion coefficients were measured as a function of polymer concentration for both polymers in dilute solution. We found that the diffusion coefficients remained relatively constant in the concentration regimes investigated and Dfast and Dslow for both polymers differed by about 1½ orders of magnitude: 1.1 × 10-6 cm2/s versus 7.8 × 10-8 cm2/s for NaPSS and 6.7 × 10-7 cm2/s versus 4.2 × 10-8 cm2/s for PEO. Also, we studied more concentrated solutions of PEO without salt and used Dfast and Dslow to calculate hydrodynamic radii of single and aggregated PEO chains. Using a concentration-dependent viscosity for PEO in water, we found single chain radii from 1 to 5 nm and aggregate radii from 45 to 60 nm.
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Leach, Kathryn Amanda. "Kinetics and morphology of electric field -induced patterning in thin polymer films." 2005. https://scholarworks.umass.edu/dissertations/AAI3194033.
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Electrohydrodynamic instabilities in thin liquid polymer films are generated when electrostatic pressure overcomes surface tension, leading to amplification of fluctuations at the polymer surface. The growth kinetics of these fluctuations are, in principle, similar to the growth in size of domains during phase separation of polymer mixtures. Consequently, an exponential dependence of fluctuation height on time, characterized by a time constant, can be predicted from the strength of the electric field and the characteristics of the polymer. Results for in situ measurements of fluctuation growth in polydimethylsiloxane show good agreement with theory at early stages and divergence from theory at later stages. At the early stages, the measured time constants shoe quantitative agreement with theory, using no adjustable parameters. Furthermore, a significant reduction in the rate of amplification was observed when a low-viscosity thiolene mixture was used. To preserve the fluctuations and patterned structures, the low molecular weight liquid could be polymerized using ultraviolet light. In situ observation of the growth and decay of electrohydrodynamic instabilities in varying electric fields showed that, since the time scales are predictable, they can be manipulated by varying the electric field. When the electric field was cycled between low and high, growth and decay of fluctuations in the varying electric fields was observed. Electric fields were also used to generate patterns in polymer/polymer/air trilayers with a PS film sandwiched between a silicon substrate and a layer of PMMA. The degree to which the viscosity of the polymer film at the substrate is smaller than that of the upper layer has a strong effect on the morphology of structure formation. Several unique three-dimensional microstructures are made possible by tuning electric-field induced fluctuations in concert with dewetting. The kinetics of structure formation were enhanced by this configuration resulting in much faster patterning than achieved in prior studies. External electric fields were also used to amplify fluctuations in bilayers with block copolymers added to reduce interfacial tension. A significant reduction in characteristic length scale for the instabilities was observed. This process shows promise for application to nanometer-scale lithography.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Windows MediaPlayer or RealPlayer.
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Mowery, Daniel Michael. "Investigation of the structure of cold -drawn high -density polyethylene using solid-state NMR." 2002. https://scholarworks.umass.edu/dissertations/AAI3068580.
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In this dissertation, the cold-drawing response of a commercial high-density polyethylene (HDPE) resin has been studied using solid-state nuclear magnetic resonance (NMR) spectroscopy and variety of other complementary techniques. Melt-crystallized, isotropic samples of the HDPE have been drawn to various extensions at ambient temperature (21°C) and at a relatively slow strain rate (0.0013 s−1). Using solid-state NMR, the first unambiguous evidence for a major morphological component intermediate to the crystalline and amorphous domains in the cold-drawn HDPE microstructure has been found. Employing an ‘inverse 13 C T1 filter’ and other filtering techniques, signals from the various components have been selected and compared. The intermediate component comprises chains of all-trans conformation but with significant disorder in packing. The chains show fast, intermediate-amplitude motions about their axes and are generally aligned with the draw direction, but with a greater distribution of orientation angles relative to crystalline phase. A quantitative 13C NMR procedure has been utilized in the analysis of morphological component composition during cold drawing. In the undeformed material, the NMR-derived composition shows excellent agreement with other common techniques. The mass fraction of the intermediate component has been measured by NMR to be as high as 35% in the cold-drawn HDPE, greater than the contributions from the amorphous domains and monoclinic crystals. The intermediate component content dramatically increases by 240% just after necking, along with a doubling in the monoclinic crystals. At the same time, decreases of about 25% in the total crystalline and amorphous phases occur. A general re-ordering in the microstructure takes place during neck propagation and strain hardening. The total crystallinity rises by about 8%, with a corresponding decrease in the monoclinic crystals (50%) and amorphous material (30%). Based on 1H spin diffusion data, a microstructural model of cold-drawn HDPE is offered. The spin diffusion data identify the intermediate component with tie-molecule bundles that connect small ‘mosaic block’ crystallites (ca. 10–15 nm side dimension) along the draw direction. The bundles consist of about 30 chains and are estimated to be about 2.5 nm in diameter and 3 nm in length.
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Zheng, Lei. "Polyolefin cubic silsesquioxane nanocomposites." 2002. https://scholarworks.umass.edu/dissertations/AAI3068607.
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This thesis focuses on the synthesis and characterization of polyolefin nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) units. Two copolymerization methods were developed utilizing either ring-opening metathesis polymerization or metallocene-catalyzed reactions to incorporate cubic silsesquioxane into polyolefins. Ring-opening metathesis copolymerizations of cyclooctene and the POSS-norbornylene macromonomer have been performed using Grubbs' catalyst RuCl2(=CHPh)(PCy3)2. Random copolymers have been prepared and characterized with POSS loadings as high as 55 wt%. Diimide reduction of these copolymers affords polyethylene-POSS random copolymers. Polyethylene (PE) and isotactic polypropylene (PP) copolymers incorporating POSS have also been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. A wide range of POSS concentrations was obtained in these polyolefin POSS copolymers under mild conditions; up to 56 wt% for PE-POSS copolymers and 73 wt% for PP-POSS copolymers were prepared. Copolymerizations of styrene and the POSS-styryl macromonomer have been performed using CpTiCl 3 in conjunction with MAO. Random copolymers of syndiotactic polystyrene and POSS copolymers have been formed and characterized. Novel nanocomposites of PE-POSS have been characterized using Wide Angle X-ray Scattering (WAXS). From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn sample, we conclude that POSS forms anisotropically shaped crystallites. On the basis of this result, a novel approach to obtain nanocomposites containing inorganic nanolayers is proposed. Cubic silsesquioxane (POSS) nanoparticles are used to achieve the nanolayered “clay-like” structure through controlled self-assembly. The organic polymer, covalently connected to POSS, is intended to regulate the POSS crystallization into a two-dimensional lattice. The concept is demonstrated by random copolymers of polybutadiene and POSS. The data from WAXS and transmission electron microscopy clearly show the formation of lamellar nanostructure of POSS aggregates, which bares the similarity at low POSS loadings to the morphology of exfoliated polymer clay nanocomposites. By taking the advantage of controlled interactions between polymer chains, we open the door to the design of polymeric materials at important nanometer length scales beyond their primary sequence length. Ultimately, this may provide materials with properties bridging the performance gap between polymer and ceramics.
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Seurer, Bradley. "Synthesis and characterization of novel thermoplastic elastomers employing polyhedral oligomeric silsesquioxane physical crosslinks." 2008. https://scholarworks.umass.edu/dissertations/AAI3315482.
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Polyhedral oligomeric silsesquioxanes (POSS) are molecularly precise isotropic particles with average diameters of 1-2 nm. A typical T 8 POSS nanoparticle has an inorganic Si8O12 core surrounded by eight aliphatic or aromatic groups attached to the silicon vertices of the polyhedron promoting solubility in conventional solvents. Previously, efficient synthetic methods have been developed whereby one of the aliphatic groups on the periphery is substituted by a functional group capable of undergoing either homo- or copolymerization. In the current investigations, preparative methods for the chemical incorporation of POSS macromonomers in a series elastomers have been developed. Analysis of the copolymers using WAXD reveals that pendant POSS groups off the polymer backbones aggregate, and can crystallize as nanocrystals. From both line-broadening of the diffraction maxima, and also the oriented diffraction in a drawn material, the individual POSS sub-units are crystallizing as anisotropically shaped crystallites. The formation of POSS particle aggregation is strongly dependent on the nature of the polymeric matrix and the POSS peripheral group. X-ray studies show aggregation of POSS in ethylene-propylene elastomers occurred only with a phenyl periphery, whereas POSS particles with isobutyl and ethyl peripheries disperse within the polymer matrix. By altering the polymer matrix to one containing chain repulsive fluorine units, aggregation is observed with both the phenyl and isobutyl peripheries. Altering the polymer chain to poly(dimethylcyclooctadiene), POSS aggregates with isobutyl, ethyl, cyclopentyl, and phenyl peripheries. The formation of POSS nanocrystals increases the mechanical properties of these novel thermoplastic elastomers, including an increase in the tensile storage modulus and formation of a rubbery plateau region. Tensile tests of these elastomers show an increase in elastic modulus with increasing POSS loading. The elongation at break was as high as 720%. Cyclic tensile test show some hysteresis of the elastomers. However, the curves show Mullins effect behavior, commonly seen in elastomers. Elastomers with POSS dispersion, however, show poor mechanical properties. These results demonstrate the novel material property gains by the incorporation and aggregation of POSS in thermoplastic elastomers, as well as the influence of the POSS periphery.
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Calzia, Kevin J. "Molecular aspects of yield and fracture in glassy thermosets and their nano-composites." 2006. https://scholarworks.umass.edu/dissertations/AAI3242098.
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The ability to fundamentally understand how changes in the molecular architecture and reinforcement at the molecular and nano-scale effect the mechanical and thermal behavior of glassy thermosets is of considerable interest. A series of epoxy-based networks with controlled molecular weight between crosslinks and backbone stiffness are utilized to identify characteristics that govern yield behavior. Two parameters, the glass transition temperature, Tg, and cohesive energy density, Ec, are identified to describe changes in network stiffness and strength, respectively. The parameters are incorporated into a model that describes yielding over a range of stress states, strain rates, and temperatures. The same epoxy network is used to explore the effects of backbone stiffness and crosslink density on the strain hardening modulus and fracture. It is found the strain hardening modulus is directly related to the crosslink density of the network similar to a traditional rubber. The backbone stiffness appears to have no effect on several post-yield phenomena. A class of compounds labeled molecular fortifiers are then incorporated into the model epoxy network. Two phosphorus-based compounds, one that is included as a free additive and another that is covalently bound to the network, are shown to improve a range of mechanical, physical, and thermal properties. The covalently bound fortifier increases the crosslink density through specific physical bonding interactions and alters the characteristics of the network. In addition several sulfur and a carbon-based compound are investigated as possible molecular fortifiers. The phhysical interactions in the interphase region are found to be enhanced in nano-clay composites that contain fortifiers. These interactions lead to improved mechanical and thermal characteristics over composites utilizing commercially modified nano-clays.
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Phuvanartnuruks, Vipavee. "Polymer surface chemistry: Surface mixtures, supported polyelectrolyte multilayers and heterogeneous chemical modification." 1997. https://scholarworks.umass.edu/dissertations/AAI9809386.
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This dissertation is divided into three parts that summarize three discrete projects that are related only in their overall objective of using chemistry to rationally control polymer surface structure and properties. Each part involves polymer surface modification, but the three employ very different techniques to effect surface-chemical changes. The first part (Chapter 1) involves the preparation of surfaces containing controllable mixtures of two functionalities (alcohol/ester or hydrocarbon ester/fluorocarbon ester) from alcohol-functionalized poly(chlorotrifluoroethylene) (PCTFE-OH) and the studies of their wetting behavior as a function of composition and structure. Contact angle analyses indicate that sequential and competitive esterifications yield mixed surfaces consisting of the two functional groups distributed randomly, while compositionally similar, patchy mixed surfaces can be prepared by partial hydrolysis/re-esterification under some specific conditions. Greater contact angle hysteresis was observed on the patchy surfaces. The second part (Chapter 2) describes the layer-by-layer deposition of cationic (polyallylamine hydrochloride (PAH)) and anionic (polysodium styrenesulfonate (PSS)) polyelectrolytes onto the PCTFE-OH substrate. XPS and contact angle data indicate that the assembled layers are stratified even though the individual layers are extremely thin (0.3-4.1 A). This thickness depends both on the charge density of the first layer of PAH (controlled using pH) and the ionic strength of the PSS adsorption solution. The stoichiometry of the assembly process also varies with the ionic strength of the PSS adsorption solution. The third part (Chapter 3) involves the heterogeneous (gas-solid) chemical modification of poly(trifluoroethylene) (PF$\sb3$E). Chlorination of PF$\sb3$E is a surface-selective reaction and the extent of chlorination can be controlled by time and light intensity. The fluorination of PF$\sb3$E carried out using 5% F$\sb2$/N$\sb2$ yields products that exhibit similar surface properties to poly(tetrafluoroethylene) (PTFE). Very thin coatings of PF$\sb3$E on inorganic supports (Si wafers) were prepared by the adsorptions from THF:toluene solutions. The higher the toluene composition, the more polymer adsorbs and the rougher the substrate becomes. The amount of PF$\sb3$E adsorption is increased significantly by introducing a polar functional group to the polymer by maleation.
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Arora, Kelyn Anne. "Preparation and characterization of microcellular foams processed in supercriticaln carbon dioxide." 1999. https://scholarworks.umass.edu/dissertations/AAI9932288.
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The aim of this research program was to elucidate the process-structure-property relationships that occur in the fabrication of microcellular foams using supercritical (SC) CO2. The first goal was to develop an understanding of the microcellular foaming process for a homogeneous system (polystyrene was chosen as a model). Rapid decompression of a SC CO2-saturated substrate at sufficiently high temperatures (above the depressed Tg) yields expanded microcellular foams. Foam structure and density can be controlled by manipulating processing conditions such as temperature, pressure, depressurization profile and vessel geometry. The foams were found to have either isotropic or transversely isotropic monodisperse cells ranging from 0.5 to 100 μm in diameter. The foamed samples either retained the geometry of the initial substrate or were expanded into the shape of the vessel in which they were made, depending on the conditions. The compressive behavior and microcellular collapse mechanisms of the polystyrene foams produced in SC CO2 were evaluated. The effects of cell geometry on the compressive strength were determined, and a buckling model was used to explain the results. The foams were found to have yield strengths exceeding those of conventional foams of equivalent density. The microcellular buckling mechanisms have been identified and it was found that collapse proceeds in a heterogeneous, progressive fashion. By analysis of the collapse behavior as a “reverse necking” phenomenon, a model was developed, using energy balance arguments, that describes the energy required for microcellular collapse. Additional studies were performed that explored the effects of material heterogeneity, constrained boundary conditions, temperature, and strain rate on the mechanical properties of the foams. Polymer blends having kinetically trapped morphologies were made via the supercritical CO2-assisted infusion of styrene monomer into and subsequent free-radical polymerization within solid polymer substrates. Blend composition and phase morphology were controlled by varying monomer concentration, reaction time and reaction temperature. Annealing studies were performed to evaluate the stability of the blends. Attempts to expand poly(tetrafluoroethylene- co-hexafluoropropylene (FEP)/polystyrene blends into composite foams were unsuccessful due to large scale phase separation. Expansion of poly(4-methyl-1-pentene) (PMP)/polystyrene blends was successful, and experiments were carried out to determine the effects of blend composition and phase morphology on foam structure.
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Sill, Kevin N. "Quantum dot - polymer nanocomposites: New materials for dispersion, encapsulation, and electronic applications." 2006. https://scholarworks.umass.edu/dissertations/AAI3242311.
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Tremendous advances in the synthesis and functionalization of nanoparticles over the past twenty years have resulted in remarkable discoveries in the field of nanotechnology. One such development is found in quantum dots, semiconductor nanoparticles that exhibit unique optical and electronic properties not found in the bulk. Research efforts associated with the combination of quantum dots and polymers center on uniting the mechanical or processing properties of the polymer with the optical properties of the quantum dot. Simply blending polymers with nanoparticles typically leads to nanoparticle aggregation, which negates the inherent advantageous properties of the quantum dots. The development of organic and polymer ligands for nanoparticle surface modification enables the preparation of dispersed nanocomposites that retain, or even enhance, the original nanoparticle properties. Presented here is the synthesis of functionalized nanoparticles that are tailored for the growth of polymers directly from the particle surface. Initial studies focused on the preparation of nanoparticle-polymer hybrid materials where the nanoparticles were evenly dispersed throughout the polymer. A method was developed to cross-link polymers grafted from the nanoparticle in an encapsulating shell, with the goal of minimizing nanoparticle degradation. In addition, polymerization chemistry from quantum dot surfaces was modified and optimized to produce conjugated polymer-quantum dot composites. The coupling of these two electronically active components gave composite materials with very unique optical properties that hold potential as displays, sensors, and light-emitting materials.
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Gobran, David A. "Phase separation and morphology of diblock and segmented block copolymers." 1990. https://scholarworks.umass.edu/dissertations/AAI9101634.
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Bulk morphologies and microphase separation behavior were studied as a function of composition and temperature for two-component (AB) diblock copolymers and as a function of composition and processing conditions for two-component segmented block copolymers. For the diblock study, well characterized, low molecular weight poly(styrene-isoprene) diblock copolymers (polystyrene volume fractions: 0.21-0.76) were examined with small angle X-ray scattering (SAXS) as a function of temperature to investigate the nature of order-order and order-disorder transitions near the microphase separation transition (MST). Data from these samples was used to develop a comprehensive morphology diagram, near the MST, as a function of $\sb{\chi}$N and composition. These results are compared with MST theories of Leibler and of Fredrickson and Helfand to provide a critical test of their predictions. Near a volume fraction of 0.5, both theories are shown to be relatively accurate, but at compositions far from 0.5 experimental results show that the two blocks are considerably less compatible than has been predicted. The absence of predicted order-order transitions near the MST indicates that composition fluctuation effects are important for low molecular weight diblocks. Further from the MST, an order-order transition was observed in a single sample as a function of temperature. The second study was an investigation of the effect of composition and processing conditions on microphase separation of segmented polyurea block copolymers used for reaction injection molding (RIM). Polyurea block copolymers polymerized in a RIM system were compared with solvent-cast solution polymerized polyureas of the same compositions (hard segment weight fractions: 0.11-0.66) to examine the effect of processing conditions. The Debye correlation function model, which assumes a random two-phase structure with no long or short range order and randomly shaped domains, was found to fit the SAXS data for the entire series of polyureas very well. Except at the highest hard segment content, the degree of phase separation, measured from the SAXS invariant, was higher for the RIM materials than the solution polymerized polyureas. This higher degree of phase separation correlates well with the better mechanical properties of the RIM samples.
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Connolly, John Michael. "Dynamic mechanical, dielectric and magnetic resonance spectroscopy of ionomers." 1990. https://scholarworks.umass.edu/dissertations/AAI9100515.
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The incorporation of a small amount of ionic groups on a hydrocarbon polymer backbone profoundly alters its thermal, rheological and electrical properties. During this study, the effects of ionic content, neutralization level and processing history on ionic group mobility have been clarified. Randomly sulfonated polystyrenes (SPS) along with their sodium and zinc salts were prepared and carefully characterized via element analysis, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). These techniques all indicate a reduction in polymer chain mobility by enhanced glass transition temperatures (T$\sb{\rm g}$) and rubbery plateau moduli and decreased dielectric relaxation strength with increasing sulfonation and neutralization levels. In addition, the importance of processing history was observed through increased rubbery plateau moduli and ionic transition temperatures with increasing molding temperature. A secondary relaxation mechanism associated with ionic domains was revealed by the failure of the Williams-Landel-Ferry (WLF) equation to describe frequency plane shifts of DMTA and DETA data. These results are consistent with a model of ionomer morphology in which polar groups phase separate into thermally labile ionic crosslinks of high functionality with trapped hydrocarbon inclusions. For comparison with recent theories on relaxations of semi-crystalline polymers, a series of ethylene-methyacrylic acid(E-MAA) copolymers and their sodium salts were prepared and characterized by infra-red(IR) spectroscopy, DSC and DMTA. All E-MAA samples exhibited mechanical relaxations similar to low density polyethylene (LDPE). In the acid form, typical copolymer behavior was observed where the alpha transition temperature (T$\sb{\alpha}$) associated with the crystalline phase decreased and the beta transition temperature (T$\sb{\beta}$) or T$\sb{\rm g}$ increased with increasing MAA content. The gamma transition (T$\sb{\gamma}$) associated with local methylene segment motions remained independent of MAA content. The sodium neutralized samples displayed characteristics of a phase separated system in which T$\sb{\beta}$ was independent of MAA content, but about 5$\sp\circ$C higher than LDPE,and T$\sb{\gamma}$ decreased slightly with increasing MAA. The ionic transition temperature of E-MAA materials was found to be about 100$\sp\circ$C lower than the equivalent SPS material, indicating the weaker clustering behavior of carboxylate compared to sulfonate ionomers and the greater flexibility of ethylene- than styrene-based copolymers. Preliminary experiments probing ionic group and cation mobility in E-MAA samples on a molecular scale were undertaken using $\sp{23}$Na nuclear magnetic resonance (NMR) spectroscopy and DETA. The results indicated a broad step increase in the spin-spin relaxation time (T$\sb2$) with increasing temperature in ethylene glycol and water saturated materials. This increase was correlated with a broad dielectric "water relaxation" peak.
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Dadmun, Mark David. "Phase transitions of lyotropic liquid crystalline polymers: Effect of fluctuations and disorder." 1991. https://scholarworks.umass.edu/dissertations/AAI9207381.
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When a solution of rod-like polymers is subjected to a reduction in solvent quality, it is theoretically predicted that a biphasic system will result. This is not what is observed however as the result is gelation; the formation of a three dimensional self-supporting polymer rich network. The lyotropic system of poly ($\gamma$-benzyl l-glutamate) (PBLG) in benzyl alcohol (BA) has been studied on a molecular level as the system is brought from the high temperature phases towards the gel in hopes of understanding the processes that occur that result in gelation. Low angle light scattering and small angle neutron scattering were used to monitor the configuration of the PBLG molecule as the system was brought from the isotropic to gel phase and to study the gel itself. Quasi-elastic neutron scattering was utilized to measure the local dynamics of the PBLG molecule as the system is brought from the cholesteric to the gel phase. The results show that an aggregation of PBLG molecules exists up to 80$\sp\circ$C in the isotropic phase and the size of the aggregate changes little as the gelation threshold is approached. As gelation occurs, the size of the aggregate increase substantially. The thermal history of the solution in the isotropic phase also affects the local structure of the resultant gel. Short annealing times result in an open structure similar to an aggregate that is formed via the clustering of clusters mechanism and longer annealing times allow the aggregate to relax and results in a denser, more compact structure. Quasi-elastic neutron scattering demonstrated that the local dynamics of the polymer are continuous and unhindered in the cholesteric phase, but become more constrained and jump like as the system enters the gel phase. The effect of quenched disorder on the nematic to isotropic transition of a liquid crystal has also been studied. Using Monte Carlo simulation and differential scanning calorimetry, it was seen that quenched disorder will interrupt the ability of the liquid crystal to correlate and this will lower the transition temperature, round and lower the heat capacity peak, and possibly change the order of the transition.
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Reffner, John Richard. "The influence of surfaces on structure formation: I. Artificial epitaxy of metals on polymers. II. Phase separation of block copolymers and polymer blends under nonplanar surface constraints." 1992. https://scholarworks.umass.edu/dissertations/AAI9219485.
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In order to understand the fundamental cause of preferential lattice orientations when certain metals are vapor deposited onto oriented semicrystalline polymers, Sn deposited onto various polyolefins was investigated as a function of polymer crystallinity, crystallography, morphology and Sn deposition conditions. Crystallinity is necessary, however, the invariance of the orientations to changes in the polymer crystallography indicates that the orientation of the metal is not due to lattice matching, but the result of artificial epitaxy on anisotropic surface features related to the direction of the chain axis (possibly atomic scale surface steps parallel to the chain axis) and the shape anisotropy of the polymer crystals. Features common to many semicrystalline polymers can thus induce orientations in metal overgrowths. The influence of a spherical external surface constraint on the microphase separation of block copolymers (poly(styrene-co-butadiene) and poly(styrene-co-isoprene)) and block copolymer-polystyrene homopolymer blends was investigated by producing very small droplets of the polymers via an aerosol technique. In microdroplets, compositions which exhibit bulk lamellar, OBDD, cylindrical and spherical morphologies result in concentric packing of lamellae, concentric disordered 'honeycomb-like' layers, layers of curved cylinders and irregularly packed spheres respectively. This constraint changes the magnitude of various contributions to the free energy, the respective roles of which can be better understood by observing which structures are produced. External surface energy is the strongest influence, resulting in the spherical microdroplets with uniform surface coatings of the lower surface free energy diene component. Maintaining preferred separations between adjacent intermaterial dividing surfaces (IMDS), which were approximately equivalent to those in the corresponding bulk structures, was also a dominant factor. Except for spherical microdomains, the observed IMDS exhibit radially dependent shapes and curvatures. Locally this results in additional interfacial area relative to the bulk, but likely provides a minimum in interfacial area given the microdroplet spherical geometry and required separations of adjacent IMDS. The most accommodating factor is the IMDS curvature. Rather than create interfacial area by truncation of the continuous microdomain morphology at the surface of the droplet, the structures curve to fit within the spherical external constraint by adopting radially periodic, concentrically ordered morphologies.
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Athanasiou, Cynthia Dawn. "The modification of epoxy/amine resin systems with poly(ether imide)." 1995. https://scholarworks.umass.edu/dissertations/AAI9606485.
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A diglycidylether of bisphenol A, DGEBA, base epoxy resin has been modified with several different types of poly(ether imide)s with the goal of increasing the toughness of this high Tg epoxy system. Initially, Ultem$\sp\circler $ 1000-1000 from GE was blended into Epon 828/DDS. Phase separated systems resulted with a 2.5-fold increase in the fracture energy over the neat epoxy resin (676 J/m$\sp2$ vs. 265 J/m$\sp2).$ As seen under the SEM, the included phase pulled out of the continuous phase, indicating poor adhesion between the two phases. Next an amine terminated poly(ether imide), ATPEI, of Mn equal to 8600 was reacted into the same epoxy resin system. There was no increase in the fracture energy with the addition of the ATPEI except at the 40 weight percent loading level. At this level, the fracture energy was comparable to that of the 40% Ultem$\sp\circler$/E828/DDS (700 J/m$\sp2).$ Phase separation was not observed in the TEM above 10 weight percent of the ATPEI in the E828/DDS. A mix of the Ultem$\sp\circler$ and the ATPEI were added to the epoxy resin with favorable results. Phase separation was present. Good adhesion between the phases was evident. And at 20 weight percent, the mixed PEI modified E828/DDS had a higher fracture energy than either of the other two systems investigated previously in this study (409 J/m$\sp2$ for the mix vs. 176 J/m$\sp2$ for the ATPEI and 353 J/m$\sp2$ for the Ultem$\sp\circler).$ Finally, an amine terminated poly(ether imide) with Mn equal to 25,500 was reacted into the same epoxy resin. The fracture energy at 20 weight percent was higher than any of the systems studied previously (451 J/m$\sp2$ vs. 409 J/m$\sp2$ for the mixed PEI modified system). Phase separated morphologies occurred at lower loading levels than anticipated-co-continuous at 20% and phase inverted at 30%. In all cases the Tg's remained above 200$\sp\circ$C.
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Macon, David James. "Thermal and mechanical behavior of rubber systems." 1997. https://scholarworks.umass.edu/dissertations/AAI9721477.
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The study of the physical behavior of rubbery materials is motivated by the desire to use these materials in a variety of environments, different mechanical conditions, and at different temperatures. For this to be possible, accurate testing conditions and modeling schemes need to be devised. These tests can be difficult to perform and existing mathematical models often neglect several basic physical requirements. One model is the statistical thermodynamic approach for calculating the thermoelastic behavior of an ideal rubber network, which assumes affine deformation of crosslinked junctions and no internal energy change with isothermal deformation. Yet, when the same relations have been manipulated according to the laws of thermodynamics, an internal energy contribution is revealed. This result is an artifact of improperly referencing strain measures and elasticity coefficients with regard to temperature. When a proper strain reference state is selected, thermoelastic stress-strain-temperature relations result that are totally entropic yet reduce to the usual isothermal conditions. This work proposes a phenomenological model that accurately models existing thermoelastic data. Experimental methods to determine the entropic and energetic contributions to rubber elasticity usually focus on the force-temperature behavior of a uniaxial sample held at constant length. Ideally, these thermoelastic measurements would be made at constant volume. Measurements are made at constant pressure and require complex corrections. It is demonstrated that two dimensionally constrained membrane samples can overcome these difficulties. By using time-average vibrational holographic interferometry, the two principal stresses of a membrane in anisotropic biaxial extension can be directly determined as a function of temperature. This two dimensionally constrained stress-temperature response greatly simplifies the resulting mathematical relations and yields no difference between constant pressure and constant volume manipulations of the data for several forms of the strain-energy function. This technique also eliminates problems inherent to the usual approaches to equilibrium thermoelastic measurements. Chemical stress relaxation of rubbers is another problem that is poorly addressed. Experiments to measure this phenomenon are conducted by measuring the force of a uniaxially constrained sample is monitored as a function of time. Holographic interferometry is an advantageous method for measuring this type of problem.