No description available.

No description available.

<p> Self-consistent field theory (SCFT) is a well established theoretical framework for describing the thermodynamics of block copolymer melts and blends. Combined with numerical methods, the SCFT can give useful and accurate predictions regarding the phase behavior of polymer blends. </p> <p> We have applied SCFT to study the phase behavior of blends composed of diblock copolymers (AB) and homopolymers (C). Two cases are studied in detail. In the first case the homopolymers have a repulsive interaction to the diblock copolymers. We found an interesting feature in the phase diagram that there exists a bump of the phase boundary line when A is the majority-component. In the second case, the homopolymers have an attractive interaction to one of the blocks of the diblock copolymers. A closed-loop of microphase separation region forms for strong interactions. For both cases, we have investigated the effects of homopolymer concentration, homopolymer chain length, and monomer-monomer interactions, on the phase behavior of the system. </p> <p> We also investigated micelle formation in polymer blends. Diblock copolymers (AB) blended with homopolymers (A) can self-assemble into lamellar, cylindrical and spherical micelles. The critical micelle concentrations for different geometries are determined using self-consistent field theory. The effect of varying copolymer block asymmetry, homopolymer molecular weight and monomer-monomer interactions on micelle morphology are examined. \\Then the blends are confined between two flat surfaces, the shape of the micelles may differ from that of the bulk micelles. We study the shape variation of a. spherical micelle under confinement and its dependence on the film thickness and surface selectivity. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

No description available.

Luminescent emission of non-fully conjugated homopolymers was successfully demonstrated as light emitting diodes (LEDs) in this research. Coil-like heterocyclic aromatic poly[2,2-(2,5-dialkyloxyphenylene)-4-4¡¦-hexafluoroisopropanebibenzoxazo- les] (6F-PBO-CnOTpA, with n = 10, 15, and 20) was synthesized, and polymer composites of 6F-PBO-CnOTpA was in-situ synthesized with acidified multi-wall carbon nanotube (MWNT- COOH). The non-fully conjugated coil-like heterocyclic aromatic homopolymer was synthesized by reacting 2,2,bis-(3-amino-4-hydroxy[henyl]-hexafluoropropane with 2,5-dialkyloxyterephthalic acid (CnOTpA) for 6F-PBO-CnOTpA, with n = 10, 15, and 20. In addition, MWNT was acidified for connecting the carboxylic group (-COOH) to reduce its aspect ratio and entropy induced aggregation. MWNT-COOH was analyzed using elemental analysis (EA) and viscometry to validate the effects of acidification period. The EA result seemed to suggest that the oxygen content increased, and the carbon and the hydrogen contents decreased with acidification period. The inherent viscosity (£binh) decreased according to acidification period suggesting that the aspect ratio was indeed decreased. A hole transport layer of PEDOT¡GPSS was applied for multi-layer LEDs,. The LEDs all showed a threshold voltage about 4 V also for the composites of 6F-PBO-CnOTpA in-situ polymerized with MWNT-COOH. The 6F-PBO-CnOTpA LEDs with and without MWNT-COOH showed an electroluminescence emission range of 400 to 750 nm.

Drinking water contaminated with arsenic is a worldwide problem, especially in developing nations. The research presented in this dissertation describes two major goals: development of hybrid homopolymer polyacrylonitrile (PAN)-based sorbents for arsenate removal from drinking water and understanding regeneration of arsenate from ferric hydroxide-based adsorbents. The homopolymer PAN fiber was chemically modified to introduce functional groups using NaOH and hydrazine hydrate (HH) separately, or in combination of both. The modified fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and ion exchange measurements. The ferric hydroxides were impregnated onto functionalized fibers using two iron loading procedures. The best arsenate removal performance was obtained using the simplest pretreatment procedure of soaking in 10% NaOH at 95 °C for ninety min, followed by precipitation coating of ferric hydroxide. This suggests that adsorbents based on a low-cost PAN fabric may be produced in developing areas of the world where commercial products may not be available. A density functional theory (DFT) molecular modeling was used to compare free energies of reactions and activation barriers in the formation of arsenate-ferric hydroxide complexes. Slow kinetics associated with arsenate adsorption and desorption attributed to the high activation barriers in forming and breaking bonds with the ferric hydroxides. Another aspect of regeneration study focused on the effects of underlying properties of the ferric hydroxides-loaded adsorbents on arsenate recovery. The arsenate loaded ferric hydroxide adsorbent containing no or weak base functionalities can be regenerated using NaOH, while addition of NaCl to NaOH solution is required for same recovery of arsenate from the adsorbents containing strong base anion exchange functionalities. Moreover, the irreversible fraction of arsenate on the adsorbent can be reduced by increasing the concentration of NaOH. Thus, understanding arsenate desorption kinetics and effects of support properties of ferric hydroxide-based adsorbents are important for environmental fate of arsenate and in designing adsorption systems for removing arsenate from potable water.

We present comparative results from simulations of a lattice and an off-lattice model of a homopolymer, in the context of kinetics of the collapse transition. Scaling laws related to the collapse time, cluster coarsening and aging behavior are compared. Although in both models the cluster growth is independent of temperature, the related exponents turn out to be different. Conversely, the aging and associated scaling properties are found to be universal, with the nonequilibrium autocorrelation exponent obeying a recently derived bound.

<p>The phase behavior of AB diblock copolymers mixed with C homopolymers (AB/C), in which A and C are capable of forming hydrogen-bonds, is examined using self-consistent field theory. The study focuses on the modeling of hydrogen-bonding in polymers. Specifically, we examine two models for the formation of hydrogen-bonds between polymer chains. The first commonly used model assumes a large attractive interaction parameter between the A/C monomers. This model reproduces correct phase transition sequences as compared with experiments, but it fails to correctly describe the change of lamellar spacing induced by the addition of the C homopolymers. The second model is based on the fact that hydrogen-bonding leads to A/C complexation. We show that the interpolymer complexation model predicts correctly the order-order phase transition sequences and the decrease of lamellar spacing for strong hydrogen-bonding. Our analysis demonstrates that hydrogen-bonding of polymers should be modeled by interpolymer complexation.</p> / Master of Science (MSc)

Des masques polymères à porosité contrôlée sont fabriqués à partir de films minces de copolymères à blocs auto-organisés polystyène-b-polylactide (PS-PLA) et polystyrène-b-poly(méthacrylate de méthyle) (PS-PMMA). Les films doivent être réorganisés grâce à une exposition aux vapeurs de solvant (THF ou DCE) pour obtenir des cylindres perpendiculaires à la surface, dans le volume et arrangés de façon hexagonale à longue distance. L’extraction sélective des domaines minoritaires conduit alors à des films minces poreux de PS. La mise en place de nouvelles techniques de caractérisation (analyse des images AFM, analyse MEB de répliques de système poreux, ellipso-porosimétrie) a permis d’évaluer l’influence de nombreux paramètres (nature du substrat, épaisseur du film, mode de dépôt, nature du solvant, temps et mode d’exposition aux vapeurs du solvant, …) sur la morphologie des films (surface, interface substrat/film, volume) et sur la cinétique de réorganisation. Des mélanges de copolymères à blocs A-B et d’homopolymères C (PS-PMMA/PLA, PS-PLA/PMMA, PS-PLA/PEO, PS-PEO/PLA, PS-PEO/PMMA, PS-PMMA/PEO) sont également étudiés. L’ajout d’homopolymères permet dans certains cas, d’améliorer la réorganisation des films de copolymères à blocs. Il permet également une augmentation des tailles caractéristiques du système. L’homopolymère C se localise au centre des domaines du bloc minoritaire B si χA-C> χB-C et χA-C > χA-B. Par exemple, dans le cas du mélange PS-PMMA/PLA, des cylindres perpendiculaires à la surface et organisés de façon hexagonale sont observés après exposition aux vapeurs de THF avec incorporation des domaines d’homopolymères PLA au centre des domaines de PMMA. / Polymer films with controlled porosity are obtained from block copolymer thin films of polystyrene-b-polylactide (PS-PLA) and polystyrene-b-poly(methylmethacrylate) (PS-PMMA). The morphology of these films must be reorganized by solvent annealing (THF or DCE) in order to obtain the cylinders perpendicular to the surface, in the volume and arranged in a hexagonal lattice over a long distance. The selective removal of the minority domains leads to a porous thin film of PS. New characterization techniques (AFM image analysis, SEM analysis of the silica replica, ellipsoporosimetry) are developed to evaluate the influence of various parameters (substrate nature, film thickness, method of deposition, duration and method of solvent vapors annealing …) on the morphology of the film (surface, interface and volume) and on the kinetics of reorganization. Blends of copolymer/homopolymer A-B/C (PS-PMMA/PLA, PS-PLA/PMMA, PS-PLA/PEO, PS-PEO/PLA, PS-PEO/PMMA, PS-PMMA/PEO) are also studied. In some cases, the addition of homopolymers can improve the reorganization of block copolymer films. It also allows an increase of the characteristics size of the system. Homopolymers C locate at the center of the minority B domains if χA-C> χB-C and χA-C> χA-B. For example, in the case of PS-PMMA/PLA blends, cylinders perpendicular to the surface and hexagonally arranged are observed after exposure to vapor of THF with incorporation of PLA homopolymer in central PMMA domains.