Current Position: Research Engineer, Syngenta
Undergraduate Institution: Virginia Polytechnic Institute and State University
Ph.D. Thesis Research:
Polymers exhibit a significant transition in material properties whenever a large change in their relaxation dynamics occurs. The timescale of relaxation for polymer chains is dependent on temperature. The temperature at which the polymer chains relax in the same timescale as the experiment is referred to as the glass transition temperature, Tg. Above Tg, polymers are able to relax and eventually flow. Below Tg, polymer chains are essentially frozen and the polymer behaves like a solid at observable timescales. Deviations of Tg from bulk values have been observed in the presence of interfaces. Previous studies have investigated the effects of the interface between two covalently bonded amorphous polymer blocks as well as the effects of non-bonded interfacial interactions between a polymer and a surface on local chain dynamics. These studies have shown correlations between the local dynamics of the polymer and the distance from the interface through a fluorescence-based technique.
My study proposes to investigate the effects of the interface present in semi-crystalline polymers. Semi-crystalline polymers contain a crystalline region and an amorphous fraction. The crystalline region is comprised of ordered polymer chains, while the amorphous fraction is comprised mostly of an entangled network of polymer chains. The difference in order causes a change in polymer chain density. However, the chain density across the interface must be the same. Therefore, we expect a gradient in chain density within the amorphous fraction, which causes a gradient in local chain dynamics. In my work, we plan on using hydrogenated polynorbornene as the semi-crystalline polymer as it is able to crystallize even while highly atactic and with high levels of chain defects. I plan to systematically increase the fluorescence label distance away from the crystalline interface via copolymerization with a monomer that is amorphous, displays similar dynamic behavior, and is excluded from the crystalline phase. Using fluorimetry, I plan on generating a spatial relationship of Tg relating to the influence of the crystalline phase.