Department of Polymer Engineering
Mechanics and Dynamics of Confined Polymers
Thin films of polymers have been used as model systems extensively due to their ability to form stabile ultrathin films that maintain their integrity. These measurements have demonstrated deviations from bulk behavior when probing their thermal properties, which are generally attributed to interfacial effects. However, the impact of these deviations on the mechanical properties is less clear. We seek to provide an improved understanding of the thermoelastic properties of these ultrathin polymer glasses. We utilize a novel approach to probing the mechanical properties of ultrathin (< 100 nm) polymer films exploiting the wrinkling instability resulting from the difference in modulus between a soft substrate (PDMS) and a glassy thin polymer film. Results from this methodology will lead to an improved understanding of the properties of confined polymer systems and will be important for microelectronics where the stability of polymer nanostructures is crucial for device manufacturing.
Our work focuses on trying to understand the fundamental origins of the observed changes in physical properties in polymer thin films. We are particularly interested in determining any relationships between chain structure/architecture and confinement; previous work utilizing a homologous series of poly (n-alkyl methacrylate)s and wide range of molecular mass of polystyrene demonstrated an apparent, direct correlation with the bulk Tg for the thin film modulus. We have also been exploring how additives can impact the size dependent properties as polymers in commercial applications generally contain many different additives.
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Block Copolymer Templated Porous Carbons
Ordered mesoporous carbons have the potential to be ubiquitous materials with potential applications including catalyst supports, membranes for separations, sensors, adsorbents, responsive electrodes, and drug delivery vehicles. Our work focuses on development of improved material properties through processing methods. Control of the structure from the atomic scale to the macroscopic scale is ultimately necessary. We are exploring multiple routes including cooperative self-assembly and vapor infiltration of preformed templates to create materials with the desired morphology. The de-coupling of reaction and self-assembly in the later route could lead to improved control of the final structure.
We seek to modify these carbons to increase its functionality and/or performance especially for electrochemical applications. The motivation for this work is the increased Li capacity of some transition metal oxides, such as TiO2, MnO2, SnO2 and V2O5, in comparison to carbon, but their low electrical conductivity limits charge transfer and hence performance. Furthermore, the charge-discharge reversibility of bulk metal oxides is generally low due to the large volume changes that lead to pulverization of the active material upon successive cycling. Addition of porosity in the material to enable expansion does provide some improvement in the cycling stability for Li battery applications, but additional improvements in cyclability occur when the metal oxide is coated with a thin carbon layer. The carbon can function as physical buffering layer for large volume change. We are actively seeking to understand how morphology impacts the performance of these mesoporous carbon composites. Detailed characterization and systematic processing are utilized to probe these questions.
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Environmentally Benign Processing for Organic Electronics
There has been much effort put into the synthesis of new materials for organic-based electronics and additional emphasis on processing to improve performance. However, the solvent du jour for most polymer electronics is dichlorobenzene, which limits commercial applicability of results from the academic laboratory to an industrial setting. We seek to utilize fundamental concepts from polymer physics and insight from our experience with conjugated polymers to engineer solvent mixtures and additives to enable high performance devices without the use of halogenated solvents. An emphasis is placed upon examining the most environmentally benign solvents possible.
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