We study dynamic phase transitions in the constant-volume and constant- pressure ensembles of two different systems: a one-dimensional system of diffusive hard particles and a three-dimensional glass-former of nearly-hard repulsive particles. The dynamic transitions are observed using ensembles of trajectories biased with respect to their dynamic activity, biasing to greater or lower activities than equilibrium allows us to sample different dynamic phases. We perform finite-size scaling of the transitions with respect to sys- tem size and observation time, and compare them to first-order phase tran- sitions. The two ensembles are not equivalent in the one-dimensional model. We compare our results to analytic predictions for diffusive systems in both the active and inactive phases, there are structural signatures for both dy- namic regimes. The active phases show hyperuniform ordering and the inac- tive regimes show jamming behaviour, local jamming in the constant-volume ensemble is achieved through phase separation. In the three-dimensional sys- tem we observe a dynamic transition to a glassy inactive phase, there is no obvious structural change and the structural relaxation time increases sig- nificantly. We take configurations from the active and inactive phases and subject them to a jamming protocol in order to compare the final density of the jammed packings. Previous work shows that the inactive phase of glass-forming systems have a different distribution of vibrational modes and a higher compressibility, this suggests that the jamming behaviour should differ between the two phases. We show that jammed packings generated from inactive configurations are denser than those generated from active configurations.

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.

In this thesis we describe two separate experiments involving the use of gold nanoparticles. The first experiment looks at the use of gold nanoparticles as a localized heat source and the potential application as a cancer treatment. The second experiment, which is the real focus of this thesis, applies gold nanoparticles in the study of the free surface dynamics of glassy thin films. Gold nanoparticles have the ability to strongly absorb the energy in an incident laser beam and convert that energy into heat. Photothermal therapy is a proposed cancer treatment which exploits this ability to irreparably damage cancerous tissues surrounding gold nanoparticles. In the first chapter of this thesis we explain an experiment designed to probe the local temperatures achieved in such a process. Gold nanoparticles are used to stabilize the boundary of an inverse micelle system which contains an aqueous fluorescent dye solution on it's interior. A temperature dependent fluorescence intensity allows us to probe the temperature changes induced by laser irradiation. In the remainder of this thesis we describe a separate experiment involving the use of gold nanoparticles to study the free surface dynamics of thin glassy films. There is a growing body of evidence in the literature that thin polymer films in the glassy state exhibit heterogeneous dynamics; specifically that the first few nanometers from an air-polymer interface exhibit enhanced mobility relative to the interior of the film. The underlying mechanism responsible for this enhanced mobility remains elusive, however some believe it to be a direct consequence of the polymeric nature of these films. We describe in detail an experiment aimed at addressing this concern. We deposit gold nanoparticles onto the surface of a molecular (non-polymeric) glassy film and monitor their behaviour upon heating using atomic force microscopy. Our results clearly show the existence of enhanced surface mobility in the system studied and provide strong evidence that enhanced surface mobility should be expected in all glass forming systems.

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.

A thermodynamical framework is presented that describes the solidification of molten polymers to an amorphous as well as to a semicrystalline solid-like state. This framework fits into a general structure developed for materials undergoing a large class of entropy producing processes. The molten polymers are usually isotropic in nature and certain polymers crystallize, with the exception of largely atactic polymers, which solidify to an amorphous solid, to an anisotropic solid. The symmetry of the crystalline structures in the semicrystalline polymers is dependent upon the thermomechanical process to which the polymer is subjected to. The framework presented takes into account that the natural configurations associated with the polymer melt (associated with the breaking and reforming of the polymer network) and the solid evolve in addition to the evolving material symmetry associated with these natural configurations. The functional form of the various primitives such as how the material stores, dissipates energy and produces entropy are prescribed. Entropy may be produced by a variety of mechanisms such as conduction, dissipation, solidification, rearragement of crystalline structures due to annealing and so forth. The manner in which the natural configurations evolve is dictated by the maximization of the rate of dissipation. Similarly, the crystallization and glass transition kinetics may be obtained by maximization of their corresponding entropy productions. The restrictions placed by the second law of thermodynamics, frame indiference, material symmetry and incompressibility allows for a class of constitutive equations and the maximization of the rate of entropy production is invoked to select a constitutive equation from an allowable class of constitutive equations. Using such an unified thermodynamic approach, the popular crystallization equations such as Avrami equation and its various modifications such as Nakamura and Hillier and Price equations are obtained. The predictions of the model obtained using this framework are compared with the spinline data for amorphous and semicrystalline polymers.

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.