Browsing by Subject "Polymers"
Now showing 1 - 20 of 68
Results Per Page
Sort Options
Item A quantitative approach to modeling polymer blend compatibility(Texas Tech University, 1997-05) Mikel, Natausha J.Some of the difficulties in designing polymer blends have been hinted at in the previous section. Polymer blending, including blending of virgin and recycled polymers, is a relatively new area. Even so, a great deal of scientific research has been undertaken pertaining to this area mainly due to the recognition of the importance of this field. As a result, there is a theoretical understanding of many aspects of polymer blending. The goal of this work was to organize some of these theoretical aspects into a modeling tool to aid in the development and/or improvement of polymer blends. The emphasis of this model was on polymer/polymer blends and does not include polymer solutions which differ slightly from polymer/polymer blends in behavior. The model which was developed is based on first principals and is meant to be used as a directional tool. It does not address some aspects of blending, such as rheology, crystallization, or the kinetics of phase separation. The main focus of the modal is on determination of blend compatibility with additional exploration of methods for the prediction of physical properties ofa blend. Because these two areas of interest can be approached separately depending on the needs of the user, the model developed is essentially presented as an algorithm using different modaling approaches to address the two specific areas mentioned. This allows a user to bypass compatibility modeling in a case where property predictions are dasu-ad for a wall-defined compatible blend.Item A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem Advances in cationic graft polymerization lithography(2005) Meiring, Heather Faye; Willson, C. G. (C. Grant), 1939-Item Assembly of coordination polymers from polythioethers with conjugated backbones(2003-12) Fu, Yuan-te, 1968-; Lagow, Richard J.The syntheses, structures and electronic properties of a new class of polythioethers with conjugated backbones and their transition metal complexes are reported. Hexakis(phenylthio)-1,5-hexadien-3-yne and hexakis(isopropylthio)- 1,5-hexadien-3-yne have been synthesized and their molecular structures determined by X-ray crystallography. These compounds exhibited photoluminescence in the solid state. The self-assembly of coordination networks from reactions of these ligands with silver(I) salts is described. These coordination polymers exhibited photoluminescence in the solid state and were characterized by X-ray analysis. The electrochemical properties of these ligands and their silver(I) coordination polymers were studied by cyclic voltammetry. Octakis(methylthio)-1,3,5-hexatriene, octakis(benzylthio)-1,3,5-hexatriene and hexakis(phenylthio)-1,3-butadiene have been prepared and their molecular structures determined by X-ray crystallography. The self-assembly of the coordination polymer from the reaction of octakis(methylthio)-1,3,5-hexatriene with silver(I) nitrate is described. Polythioethers with these conjugated backbones described react as bisbidentate ligands with palladium(II) to yield dinuclear palladium complexes. Mononuclear palladium(II) and platinum(II) complexes of such ligands have also been prepared. The structures of these mononuclear and bimetallic complexes were determined by X-ray analysis. The synthesis and crystal structure of the dinuclear ruthenium(II) complex of octakis(methylthio)-1,3,5-hexatriene is also reported.Item Axisymmetric flow of dilute xanthan gum polymer solutions through media(Texas Tech University, 1984-08) Duran, Stephen LynnNot availableItem Controlled assembly of biodegradable gold nanoclusters for in vivo imaging(2015-12) Stover, Robert John; Johnston, Keith P., 1955-; Truskett, Thomas M; Fan, Donglei; Korgel, Brian; Sokolov, KonstantinGold nanoparticles are of interest in biomedical imaging applications due to their inert nature and ability to exhibit surface plasmon resonance. These phenomena can result in high near-infrared extinction (NIR) due to asymmetry or close interparticle spacings within gold structures, making these materials ideal for photoacoustic imaging. Using this imaging modality, these materials allow for high contrast compared to the body’s tissues which exhibit a transparent “window” between 700-1100 nm, making them perfect for early cancer detection. However many gold structures designed for this application fail to achieve high NIR-absorbance at the <5 nm sizes which are required for efficient kidney clearance. Therefore, we designed a system which assembles ~4 nm primary gold particles into closely-spaced clusters of controlled size using a biodegradable, weakly adsorbing polymer and balance of colloidal attractive and repulsive forces. Thus, when the polymer degrades in acidic environments – such as within cells – the residual charge on the primary particles leads to dissociation of the clusters back to renal-clearable constituents. Since proteins in the blood and cells can increase the diameter of the primary particles above the 5 nm threshold, nanoparticle surfaces were designed to have a mixture of charged and zwitterionic molecules to limit protein interactions through buried charges and increased particle hydration. Strongly-bound, zwitterionic thiol-containing ligands were also investigated to resist the intracellular exchange of biomolecules which could compromise the clearable nature of the particles. These decorated nanoparticles were then assembled into clusters through one of two methods which varied either gold and polymer concentrations through evaporation, or particle charge via electrolyte addition prior to quenching by dilution in DI water. Once assembled, clusters assembled with polymer showed dissociation behavior after incubation in pH 5 acidic solutions to mimic the cellular pH environment. In other cases, sintering of the gold nanoparticle clusters prevented such dissociation. This thesis demonstrates the ability to not only create biocompatible nanoparticle surfaces, but to establish control size control over nanocluster assemblies which are capable of being used as NIR contrast agents.Item Damage initiation, progression and failure of polymer matrix composites due to manufacturing induced defects(Texas A&M University, 2007-09-17) Chowdhury, Khairul AlamIn polymer matrix composites (PMCs) manufacturing processes can induce de- fects, e.g., voids, fiber misalignment, irregular fiber distribution in the cross-section and broken fibers. The effects of such defects can be beneficial or deleterious de- pending on whether they cause failure suppression or enhancement by localized de- formation processes e.g., crazing, shear yielding and fiber-matrix debonding. In this study, a computational approach is formulated and implemented to develop solu- tions for general boundary-value problems for PMC microstructures that accounts for micromechanics-based constitutive relations including fine scale mechanisms of material failure. The defects considered are voids, and the microstructure is explic- itly represented by a distribution of fibers and voids embedded in a polymer matrix. Fiber is modeled as a linearly elastic material while the polymer matrix is mod- eled as an elastic-viscoplastic material. Two distinct models for the matrix behavior are implemented: (i) Drucker??????Prager type Bodner model that accounts for rate and pressure-sensitivity, and (ii) improved macromolecular constitutive model that also accounts for temperature dependence, small-strain softening and large-strain harden- ing. Damage is simulated by the Gearing-Anand craze model as a reference model and by a new micromechanical craze model, developed to account for craze initiation, growth and breakdown. Critical dilatational energy density criterion is utilized to predict fiber-matrix debonding through cavitation induced matrix cracking. An extensive parametric study is conducted in which the roles of void shape, size and distribution relative to fiber in determining damage initiation and evolution are investigated under imposed temperature and strain rate conditions. Results show there are significant effects of voids on microstructural damage as well as on the overall deformational and failure response of composites.Item Deposition of cationic polymer micelles on planar and patterned SiO₂ surfaces(2003-12) Hahn, Jungseok; Webber, Stephen E.Item Design, synthesis and testing of materials for 157 nm photolithography(2005) Chambers, Charles Ray; Willson, C. G. (C. Grant), 1939-The microelectronics industries’ ability to keep pace with Moore’s law (the doubling of the number of transistors per integrated circuit every 18 to 24 months) has been due to advances in the photolithographic process. Shrinking the feature sizes that can be printed has been accomplished by decreasing the exposure wavelength which allows higher resolution and thereby more transistors per area. Currently i-line (365 nm) and deep UV (248 nm) are the most frequently used wavelengths for integrated circuit manufacturing. As device geometries shrink below 100 nm, the lithography for critical layers will be performed at an exposure wavelength of 193 nm. The 193 nm technology is being implemented now. Some “next generation” photolithography will be used to print features down to 45 nm. The technology that has investigated the most for printing the 45 nm node is uses 157 nm as the exposure wavelength. As the move is made from one exposure wavelength to the next new photoresist materials are required that have a low absorbance at the lower wavelength. Finding materials for 157 nm photolithography was particularly challenging due to the inherently high absorbance of most materials at this short wavelength. It was discovered that the addition of fluorine into organic molecules greatly increased their transparency at 157 nm. Fluorine or other transparency enhancing moieties were therefore incorporated into analogues of the 193 nm photoresist polymers. New fluoro polymers were prepared by free radical copolymerizations of electron deficient olefins with fluorinated and nonfluorinated norbornenes. Unfortunately the transparency requirements were not fully achieved with the 193 nm photoresist polymer analogues. Highly transparent fluorinated norbornene polymers were prepared using metal catalysts. One such polymer is poly(2-(3,3,3-trifluoro-2-trifuoromethyl-2- hydroxypropyl)bicyclo[2.2.1]hept-5-ene) (PNBHFA). It was discovered that PNBHFA has unique dissolution inhibition properties which are reminiscent of the novolac resin used in two component, non-chemically amplified photoresist system used at 365 nm. A more transparent fluoropolymer (Asahi RS001 polymer) was later introduced. Transparent, highly functionalized additives that could be blended with PNBHFA or the Asahi polymer and used to print high resolution, high aspect ratio images at 157 nm were designed, synthesized and tested.Item Development of a novel EOR surfactant and design of an alkaline/surfactant/polymer field pilot(2012-12) Gao, Bo; Sharma, Mukul M.Surfactant related recovery processes are of increasing interest and importance because of high oil prices and the urge to meet energy demand. High oil prices and the accompanying revival of EOR operations have provided academia and industry with great opportunities to test alkaline surfactant polymer (ASP) methods on a field scale and to develop novel surfactant systems that can improve the performance of such EOR processes. This dissertation intends to discuss both opportunities through two unique projects, the development of novel surfactants for EOR applications and the design for an alkaline/surfactant/polymer (ASP) field pilot. In Section I of this dissertation, a novel series of anionic Gemini surfactants are carefully synthesized and systematically investigated. The remarkable abilities of Gemini surfactants to influence oil-water interfaces and aqueous solution properties are fully demonstrated. These surfactants are shown to have great potential for application in EOR processes. A wide range of Gemini structures (C₁₄ to C₂₄ chain length, -C2- and -C4- spacers, sulfate and carboxylate head groups) was synthesized and shown to have high aqueous solubility, with Krafft points below 20°C. The critical micelle concentrations (CMC) for these new molecules are measured to be orders of magnitude lower than their conventional counterparts. The significantly more negative Gibbs free energy for Gemini surfactant drives the micellization process and results in ultralow CMC. An adsorption study of Gemini surfactants at air-water and solid-water interfaces shows their superior surface activity from tighter molecular packing, and attractive characteristics of low adsorption loss at the solid surface. All anionic Gemini surfactants synthesized have an extraordinary tolerance to salinity and/or hardness. No phase separation or precipitation occurs in the aqueous stability tests, even in the presence of extremely high concentrations of mono- and/or di-valent ions. Moreover, ultra-low IFT values are reached under these conditions for Type I microemulsion systems, at very low surfactant concentrations. The stronger molecular interaction between the Gemini and conventional surfactants offers synergy that promotes aqueous stability and interfacial activity. Gemini molecules with short spacers are capable of giving rise to high viscosities at fairly low concentrations. The rheological behavior can be explained by changes in the micellar structure. A molecular thermodynamic model is developed to study anionic Gemini surfactants aggregation behavior in solution. The model takes into account of the head group-counter-ion binding effect and utilizes two simplified solutions to the Poisson-Boltzmann equation. It properly predicts the CMC of the surfactants synthesized and can be easily expanded to investigate other factors of interest in the micellization process. Section II of this dissertation studies chemical formulation design and implementation for an oilfield where an alkaline/surfactant/polymer (ASP) pilot is being carried out. A four-step systematic design approach, composed of a) process and material selection; b) formulation optimization; c) coreflood validation; 4) lab-scale simulation, was successfully implemented and could be easily transferred to other EOR projects. The optimal chemical formulation recovered over 90% residual oil from Berea coreflood. Lab-scale simulation model accurately history matches the coreflood experiment and sets the foundation for pilot-scale numerical study. Different operating strategies are investigated using a pilot-scale model, as well as the sensitivities of project economics to various design parameters. A field execution plan is proposed based on the results of the simulation study. A surface facility conceptual design is put together based on the practical needs and conditions in the field. Key lessons learned throughout the project are summarized and are invaluable for planning and designing future pilot floods.Item Development of new membranes based on aromatic polymers and heterocycles for fuel cells(2007-05) Fu, Yongzhu, 1977-; Manthiram, ArumugamProton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) have drawn much attention as alternative power sources for transportation, stationary, and portable applications. Nafion membrane is currently used in PEMFC and DMFC as electrolyte, but is confronted with a few difficulties: (i) high cost, (ii) limited operating temperature (< 100 o C), and (iii) high methanol permeability. With an aim to overcome some of the problems encountered with the Nafion membrane, this dissertation focuses on the design and development of new polymeric materials systems for use in PEMFC and/or DMFC. Sulfonated polysulfone (SPSf) membranes with various degrees of sulfonation were prepared and investigated in DMFC. With a degree of sulfonation of 50 - 70 %, the SPSf membranes exhibit low methanol permeability and electrochemical performance comparable to that of Nafion 115, making it an attractive low-cost alternative to Nafion. However, lower performance at higher current densities due to their low proton conductivities compared to Nafion is a disadvantage. It is found that the low methanol crossover is due to narrower hydrophilic channels, resulting in water/methanol confinement as in sulfonated poly(ether ether ketone) (SPEEK) membranes. Replacement of water by imidazole in Nafion helps to keep high proton conductivity at higher temperatures (> 100 o C) due to Grotthuss-type mechanism, but imidazole poisons the Pt catalyst. Interestingly, doping the Nafion-Imidazole composite membrane with H3PO4 partly suppresses the imidazole poisoning of the Pt catalyst. Employment of Pd-Co-Mo catalyst instead of Pt improves the fuel cell performance at 100 o C further due to a higher tolerance of the non-platinum Pd-Co-Mo catalyst to imidazole. Encouraged by this, benzimidazole group was then selected to promote proton conduction in the environment of sulfonic acid groups instead of imidazole (pKa = 7.0) due to its lower pKa value (5.5). Accordingly, 1,3-1H-dibenzimidazole-benzene containing two benzimidazole groups was synthesized and blended with SPSf. The blend exhibits higher proton conductivity under anhydrous conditions than plain SPSf and offers improved fuel cell performance and lower methanol crossover in DMFC. Polysulfones containing pendant N-heterocycles like benzimidazole, 2-amino-benzimidazole, or 3-amino-1,2,4-1H-triazole units were designed and synthesized. Blend membranes containing these polymers and SPEEK exhibit higher proton conductivities under anhydrous conditions as well as higher fuel cell performance due to acid-base interactions involving Grotthuss-type mechanism. They also lower methanol crossover further due to the insertion of the pendant N-heterocycles into the hydrophilic channels of SPEEK, improving the long-term stability in DMFC and reducing the Pt loading at the cathode side.Item Development of photocurable pillar arrays formed via electrohydrodynamic instabilities(2006) Dickey, Michael David; Willson, C. G. (C. Grant), 1939-As photolithography approaches both fundamental and economic barriers, interest in alternative patterning technologies has grown. This thesis focuses on two alternative patterning techniques: nanoimprint lithography (NIL) and electric field assisted assembly. NIL is a high resolution, yet inexpensive contact patterning process. Step and Flash Imprint Lithography (SFIL) is a type of NIL that involves pressing a topographically patterned template onto a substrate covered with a small volume of liquid. The liquid fills the voids of the template and is hardened by UV irradiation. Low viscosity liquids are ideal for rapid patterning. An acrylate material formulation was developed to meet the various processing needs of SFIL. Unfortunately, oxygen inhibits the free radical photopolymerization used to cure the acrylate. The effects of oxygen were characterized using a semi-empirical model that relies on rate coefficients measured by real time IR spectroscopy. The model predicts an inhibition period at the beginning of irradiation as radicals are quenched by oxygen. After the oxygen is consumed, the polymerization proceeds rapidly except at the perimeter of the template, which is subject to oxygen diffusion from the ambient. Electric field assisted assembly is another attractive patterning technique that is capable of forming polymeric pillar arrays. Pillars form by the amplification of thin-film surface instabilities through the application of an electric field normal to the film. Work to date on pillars has focused on glassy polymers that are limited by the requirement of heat to modulate the rheological properties. A focus of this thesis is on developing low viscosity materials for the formation of pillars. Low viscosity materials form pillars orders of magnitude faster than high-melt viscosity polymers. The pillars form at room temperature and are hardened by UV irradiation. In addition to developing and characterizing low viscosity materials, the aspect ratio of the pillars was optimized. The aspect ratio of the pillars was increased by physically stretching the pillars through the development of an active gap tool. Methods to improve long range order were also investigated. Electric field assisted assembly and imprint lithography are promising photolithographic alternatives that benefit considerably from the use of low viscosity materials.Item Dynamical phenomena in multicomponent polymers(2006) Narayanan, Bharadwaj; Ganesan, VenkatThis research concerns with different aspects of dynamical phenomena in the context of multicomponent polymeric systems. The polymer melts under investigation include polymer blends of varying compositions of two homopolymers (A and B), polymer emulsions of homopolymers blended with block copolymers (AB) and pure block copolymer systems. A novel computation algorithm termed the Self-Consistent Brownian Dynamics (SCBD) was developed and employed to explore the flow effects encountered in the aforementioned polymeric systems. Our contributions in polymer blend systems include, quantification of the slip phenomena at the interface of phase separated symmetric and asymmetric blends. We have also quantified the slip suppression phenomena by the addition of copolymer compatibilizers to the polymer blend interfaces. We have also used the SCBD approach to study the effect of copolymer characteristics on the dynamics of an isolated polymer droplet embedded in a matrix of another polymer. In the case of ternary polymer blend systems, we have studied the flow-induced phase transitions in the microemulsion phases. We provide molecular viewpoint suggesting that the interplay between polymer chain conformations and their flow deformations can lead to novel flow effects upon the phase, structure and rheological behavior of ternary blend systems. In the case of pure copolymer systems, we have studied the effect of oscillatory shear on the lamellar orientation of phase separated multiblock copolymers.Item The effect of supercritical fluid on polymer systems(2007) Wang, Xiaochu, 1979-; Sanchez, Isaac C., 1941-Great interest has been directed toward the study of polymer thin films recently due to their emerging applications, and appreciable deviated properties and phenomena as compared with bulk polymers. Carbon dioxide (CO₂) has received attention as an environmentally benign alternative to hazardous industrial solvents. Unlike conventional liquid solvents, the density and hence the solvent strength of supercritical CO₂ can be tuned by small variations in pressure, temperature or both. The objective of this work is to study the interaction between high pressure CO₂ and polymer systems. We introduced the methodology used in this dissertation. The combination of gradient theory of inhomogeneous systems and Sanchez-Lacombe Equation of State is used to calculate the interfacial properties, such as interfacial density profile, interfacial tension and interfacial thickness. We first investigated the adsorption of supercritical fluid on polymer surfaces. We showed analytically that surface adsorption of high pressure fluid on an attractive surface is proportional to the compressibility of the fluid. We have also investigated numerically the sorption of supercritical CO₂ on poly(dimethylsiloxane) (PDMS) and polyisobutylene (PIB), and supercritical 1,1-difluorethane on PS. By calculating the Gibbs adsorption and adsorption layer thickness of the supercritical fluids, we found in all cases that maximum adsorption occurred when the supercritical fluid was near its compressibility maximum. We then examined the compatibilization effect of supercritical fluid on two incompatible polymers. We calculated the interfacial density profile, interfacial thickness and interfacial tension between the two polymers with and without the supercritical fluid. We found that the interfacial tension was decreased and the interfacial thickness was increased with high pressure super-critical fluid for the ternary systems we have investigated. No enhancement or deleterious effects on compatibilization were observed as the critical point was approached and the compressibility became large. We also examined the morphological structures of asymmetric poly(ethylene oxide)-b-poly(1,1'-dihydroperflurooctyl methacrylate) (PEO-b-PFOMA) thin films upon annealing in supercritical CO₂. The strong affinity between PFOMA and CO₂ was found to induce phase segregation when annealing PEO-b-PFOMA films as compared with vacuum at the same temperature.Item Effects of polymer-organoclay interactions and processing methods on nanocomposite structure and properties(2006) Chavarria, Florencia; Paul, Donald R.Item Electrochemical study of the catalytic properties of cobalt 2,2'-bipyridine complexes with n-alkyl bromides and selected olefins(Texas Tech University, 1982-05) Caron, Linda MarieNOT AVAILABLEItem Electroconductive neural interfaces for neural tissue applications(2010-08) Lee, Jae Young, 1974-; Schmidt, Christine E.; Freeman, Benny D.; Maynard, Jennifer; Frey, Wolfgang; Bielawski, Christopher W.Creating effective cellular interfaces that can provide specific cellular signals is important for a number of fields ranging from tissue engineering to biosensors. Electroconducting polymers, especially polypyrrole (PPy), have attracted much attention for use in numerous biomedical applications since they provide a potential platform for local delivery of electrical stimuli to target tissues. To effectively modulate cellular functions at neural interfaces, it is essential to incorporate a range of extracellular cues into conducting polymers according to specific applications, such as nerve guidance conduits and implantable neural probes. For nerve regeneration scaffolds, three dimensional forms are desired for control of critical properties, such as porosity, mechanical strength, and topography. However, most researchers have worked on conventional two-dimensional PPy films, which cannot mimic a native three-dimensional architecture. Thus, a portion of my work has focused on introducing three-dimensional nanofibrous features into PPy. I have investigated various coating conditions to obtain uniform and conductive nanofibers. Effectiveness of electrical stimulation through the conducting nanofibers was confirmed by in vitro PC12 cell culture. The effects of different conducting nanofiber topographies (random and aligned) on cell adhesion and neurite outgrowth were examined in conjunction with electrical stimulation. The benefits of immobilized-NGF could be combined with electrical stimuli, which could be an ideal platform for neural tissue engineering scaffolds. Thus, I have modified conducting polymers to display neurotrophic activity. Nerve growth factor (NGF) was chemically immobilized on two dimensional and three dimensional PPy substrates. Specific chemical conjugation was achieved and characterized using diverse techniques. Immobilized NGF was as effective as exogenous NGF in medium in inducing neurite development and extension. NGF immobilized on functionalized PPy substrates was stable in a physiological solution and under electrical stimulation, indicating effective prolonged activity. I also investigated another important application of conducting polymer-based materials for neural interfacing - passivating electrodes with a biocompatible polysaccharide, hyaluronic acid (HA). I synthesized electrically polymerizable HA by chemically conjugating amine-functionalized pyrrole derivatives with HA. This coating was stable under physiological conditions for three months and resistant to enzymatic degradation. In vitro studies have shown the minimal adhesion and migration of astrocytes on the HA-coated electrodes. Implantation of HA-coated commercial probes into rat cortices for three weeks revealed attenuated reactive astrocyte responses from the coated wires, and the importance of glial interaction with non-conducting sites was demonstrated.Item Employing near-field scanning optical microscopy (NSOM) as a tool for interrogating a new conjugated polymer material, di-dodecyl poly(phenylene ethynylene)(2004) Imhof, Joseph Michael; Vanden Bout, David AntonChemistry and BiochemistryItem Empty space and how things move around in it(2006) Willmore, Franklin Ted; Sanchez, Isaac C.