Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 258-283).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Peter F. Green. Vita. Includes bibliographical references.

The behavior of polymeric systems confined into thin films is a situation that has numerous practical consequences. One particular application in which the properties of thin polymer films is becoming crucially important is in the design, formulation, and processing of photoresists for semiconductor microlithography. As devices continue to be scaled down into the nano-regime, the microelectronics industry will ultimately rely upon a molecular understanding of materials for process development. The majority of these devices are now confined in planar geometries; thus, thin films have played an ever-increasing role in manufacturing of modern electronic devices. This movement towards thinner resist films creates larger surface to volume ratios, and hence thin films can exhibit thermodynamic, structural, and dynamic properties that are different from those of the bulk material. It is thus extremely important to understand the properties of polymers when confined in such geometries for various applications including resists for lithographic patterning. In present work, the influence of a variety of factors including film thickness, molecular weight, and substrate interactions on the polymer thin film physical properties such as the glass transition temperature, coefficient of thermal expansion, dissolution rate, and diffusion coefficient was studied in detail using a combination of experimental characterization and molecular modeling simulation techniques.

No description available.

Photopolymerization, which uses light rather than heat to initiate polymerization, is a facile technique used to fabricate adhesives, protective coatings, thin films, photo-resists, dental restoratives, and other materials. Epoxide monomers, which are polymerized via cationic photoinitiation, have received less attention in fundamental research in comparison to free radical polymerized acrylate monomers. The characterization of propagation mechanisms, network structures, and physical properties is yet lacking. This project focused on the reactivity and physical properties of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (EEC), and the kinetic and physical effects of chain transfer agents (CTAs) in EEC based formulations were characterized. This characterization was carried out using real-time Raman spectroscopy, real-time infrared spectroscopy, dynamic mechanical analysis, simple gel fraction measurements, and atomic force microscopy. The effects of water, organic alcohols, processing conditions (e.g., UV light intensity, humidity, post-illumination curing temperature), and photoinitiation systems were investigated. In general, increasing the concentration of CTAs in a crosslinking epoxide resin increases the rate of polymerization and the overall epoxide conversion level. High CTA levels also correspond to lower glass transition temperatures (Tg) and lower crosslink densities. A post-illumination annealing was critical in obtaining stable physical properties for high Tg epoxide materials. In addition, humidity (water being the most universal contaminant type of CTA) was found to impact the surface properties of an epoxide polymer negatively by reducing the surface hardness. Hybrid acrylate-epoxide systems are much more complex and unpredictable in curing behavior. The use of hydroxy acrylates in hybrid systems allows for grafting between the epoxide and the acrylate domains, via the AM mechanism. Another intricacy of hybrid systems is the initiation system. In order to maximize the conversion of both the epoxide and the acrylate moieties, the free-radical photoinitiator must not hinder the polymerization of the epoxide monomer. Some very efficient free-radical photoinitiators limit the epoxide polymerization by absorbing the majority of the deep-UV incident photons. Finally, a renewable acrylate oligomer was synthesized to provide a green alternative to petroleum-based oligomers currently used. The oligomer was freely miscible and readily photopolymerized with a wide range of commercial monomers. The Tg relationship between the commercial monomers and the parent resin followed the Fox equation. The results of this research provide strategies for controlling epoxide kinetics and physical properties in neat and hybrid systems. This information is useful for tailoring resin formulations to specific end-use applications, especially in films, coatings, and adhesives. Hybrid epoxide-acrylate photopolymerization affords the unique opportunity to structure polymer networks in time and to engineer advanced material properties. These hybrid systems are based on formulations that contain both an epoxide moiety, which undergoes cationic ring-opening photopolymerization, and an acrylate moiety, which undergoes free-radical photopolymerization. Through the combination of these two independent reactive systems, hybrid polymers exhibit lower sensitivity to oxygen and moisture and offer advantages such as increased cure speed and improved film-forming properties. The ability to design the polymer network architecture and to tune mechanical properties can be realized through control of the cationic active center propagation reaction relative to the cationic chain transfer reaction. Specifically, grafted polymer networks can be developed through the covalent bonding of the epoxide chains to the acrylate chains via hydroxyl substituents. This work demonstrates the formation of these grafted polymer networks and overviews the physical properties obtained through control of hydroxyl content and hybrid formulation composition.

The effect of moisture absorption on the glass transition temperature (Tg) and stress/strain behavior of network polyurethane shape memory polymer (SMP) foams has been investigated. With our ultimate goal of engineering polyurethane SMP foams for use in blood contacting environments, we have investigated the effects of moisture exposure on the physical properties of polyurethane foams. To our best knowledge, this study is the first to investigate the effects of moisture absorption at varying humidity levels (non-immersion and immersion) on the physical properties of polyurethane SMP foams. The SMP foams were exposed to differing humidity levels for varying lengths of time, and they exhibited a maximum water uptake of 8.0 percent (by mass) after exposure to 100 percent relative humidity for 96 h. Differential scanning calorimetry results demonstrated that water absorption significantly decreased the Tg of the foam, with a maximum water uptake shifting the Tg from 67 °C to 5 °C. Samples that were immersed in water for 96 h and immediately subjected to tensile testing exhibited 100 percent increases in failure strains and 500 percent decreases in failure stresses; however, in all cases of time and humidity exposure, the plasticization effect was reversible upon placing moisture-saturated samples in 40 percent humidity environments for 24 h.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Derrick R. Dean, Wiliam K. Nonidez, Andrei Stanishevsky, Charles L. Watkins. Includes bibliographical references.

Not available / text

Dynamical heterogeneity (DH) has been observed in many systems approaching the glass or jamming transition. Whether DH has a structural origin is under heated debate. To provide a deeper understanding, in this thesis I investigate the microscopic dynamics in weakly attractive colloidal systems by confocal fluorescence microscopy. The van Hove density-density correlation function is applied to our systems. Separable fast and slow populations emerge in the self part (svH), while the distinct part shows a strong signature of DH close to the gel transition. At intermediate time, svH shows a purely exponential tail, mainly arising from the fast population. I show that this broad tail is a direct consequence of the occurrence of rare large jumps that are statistically distributed. The slow population tends to form a space-spanning backbone, and its mean squared displacement close to the gel transition exhibits a plateau, whose height is consistent with the range of attraction, suggesting a bonding mechanism for the dynamical arrest. I further examine various quantities characterizing local structure and local dynamics and a strong correlation is identified between them. Subsequently, I develop order parameters for quantifying amorphous structure and apply them to our systems. I find that attractive colloidal systems exhibit higher order under higher attraction tension, while hard spheres become more ordered under higher compression. Finally, I investigate the effect of the range of attraction on the structure and dynamics of attractive colloidal systems. I observe that the system with shorter range of attraction forms a denser and more heterogeneous structure. Meanwhile, I observe an even stronger dynamical heterogeneity. These observations provide further evidence of a connection between structural heterogeneity and dynamical heterogeneity in these systems, providing guidance for a theoretical description of the dynamical arrest as well as the relaxation mechanisms upon gelation and its relation to solidification in glasses. / In order to do all of this, I first implemented full 3D subpixel resolution localization of particles and improved particle tracking algorithms tailored for the sorts of heterogenous dynamics these systems exhibit, that otherwise confounds existing methods such that the very relaxation mechanisms would be missed. This allows us to obtain unprecedented precision in positions of all of the particles and complete tracking, both of which are essential for correctly determining system properties that depend on measured particle dynamics.

The production of free flowing powder by spray drying of sugar-acid rich foods requires an appropriate carrier. High molecular weight materials such as maltodextrins are commercially used as a drying aid because of their high glass transition temperature (Tg). Alternatively, fibre-rich by-products from fruit and vegetable juice processing might provide high molecular weight elements that are suitable as a drying support. This study aimed to understand the variables affecting the spray-dried product of fruit juice so that non-sticky fibre-based juice powder could be obtained. Freeze dried carrot fibre was centrifically-milled to 50-100 µm sizes. Three sugar determination methods; enzymatic, enzyme membrane and HPLC with RID, were compared. The freeze drying performance of fructose, fructose + carrot fibre and fructose + carrot fibre + malic acid had the glass transition temperatures measured by differential scanning calorimetry (DSC) at 0.1 °C min-1. The results from the freeze drying were used as a key for the possibility of spray dried apple juice + carrot fibre. Similar methods were used to study freeze dried fructose + maltodextrin (DE max 9.8) and fructose + maltodextrin + malic acid. Dried sucrose, glucose and fructose were used to study glass transition temperature of melted amorphous sugars and mixtures by the visual experiment and DSC at 0.1°C min-1 of heating and cooling scans. The Gordon-Taylor equation was used to predict the Tg of anhydrous two-sugar mixtures from experimental and literature data. The Coachman and Karaze equation was used to predict Tg of three-sugar mixtures and compared to the experimental data. Spray dried powders of fructose + carrot fibre of 30, 40, 50, 60 and 70% w/w and apple juice concentrate + carrot fibre of 30, 40, 50, 60, 70% w/w at 165/75°C inlet/outlet temperature in a laboratory scale drier were compared to that of fructose + maltodextrin (DE max 9.8) and apple juice concentrate + maltodextrin of 50, 60 and 70% w/w (dry basis). Dielectric analysis in the range 200 Hz -1 MHz between 10-105 °C were applied to find the onset Tg (based on DSC results) from freeze dried mixtures of 14, 21, and 28% w/w (dry basis) carrot fibre+ fructose. The enzymatic method was found to be the most accurate method for sugar determination of fruit juice but the HPLC method was the most practical one. The results of Tg values of sugars and mixtures melted showed that the Tg values from heating and cooling scans of fructose, glucose and sucrose were in good agreement with literature. Fructose acted as a plasticizer; an increase in the fructose fraction decreased the Tg of sugar mixtures. Sucrose increased the Tg of the mixtures while the Tg of the three-sugar mixtures was less variable when there was a moderate to high proportion of glucose. The visual Tg values of sugars and mixtures were 7-28 °C higher than the onset DSC heating and cooling Tg values. This result suggested that more than one method should be used to study the glass transition of substances. The Gordon-Taylor equation did not fit well the Tg values of the dry sugars and their mixtures from this experiment. The variations might have been due to the degradation of sugar samples on the melting process. The Coachman and Karaze equation gave a good prediction of the three-sugar mixtures from this experiment. The carrot fibre was found to be crystalline. Carrot fibre increased the Tg of freeze dried fructose and decreased stickiness of fructose. Increasing malic acid fraction decreased Tg of the mixtures. Freeze dried fructose + maltodextrin showed higher hygroscopicity than freeze dried fructose + carrot fibre. It was not possible to determine Tg of fructose + maltodextrin + malic acid due to the swelling and hygroscopicity of the freeze dried samples. Tg values of freeze dried fructose + carrot fibre and fructose + maltodextrin were found to high enough to allow spray drying of these mixtures. The minimum fraction of carrot fibre to facilitate spray drying of fructose and apple juice concentrate was found to be 30%. Mixtures with maltodextrin at a fraction lower than 50% could not be successfully spray dried. When spray drying fructose + carrot fibre, apple juice + carrot fibre, fructose + maltodextrin and apple juice + maltodextrin at the appropriate ratios most of the powder stuck to the drier walls. The powder swept from the wall was free flowing with moisture content of approximately 2-4%. The Tg values of these powder indicated the wall build-up might be avoided in larger scale drying. Tg values of spray dried powder from the mixtures with fibre and maltodextrin were found to be not very different. The yield from mixtures with carrot fibre was three times higher than those of mixtures with maltodextrin. This cast doubts that Tg alone could be a good indicator for the stickiness of spray dried material. The microscope images and DSC scans of spray dried powders of fructose + carrot fibre and apple juice + carrot fibre showed crystalline material. The particle of spray dried fructose + maltodextrin and apple juice + maltodextrin were mostly amorphous. The crystals are more physically and chemically stable than the amorphous form. Thus carrot fibre is a good additive in spray drying of fruit juice. Dielectric analysis at low frequency was able to possible detect Tg of single and double components. For food polymer with many components it was found that Tg value was not consistently dependent on frequency. In conclusion, carrot fibre was a more effective carrier for spray drying than maltodextrin when compared on a mass basis and spray drying condition. Since edible fibre is an essential element needed by the human body, spray drying of fruit juice using fibre as a carrier showed the great potential of fibre in the application of fruit juice spray drying. In the case of clear juice, after reconstitution, the fibre can be easily separated from the juice as there seemed to be no chemical binding between the juice and the fibre during the spray drying process.