STUDYING NORMAL MODES IN AMORPHOUS THERMOPLASTICS: POLY(METHYL METHACRYLATE), POLYSTYRENE, AND POLYVINYL CHLORIDE
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We have studied normal vibrational modes in three amorphous thermoplastic polymers. Our studies have focused on determining how different classes of modes interact to give rise to thermal conductivity. We have found that the modes in these systems are highly localized, even when compared to other disordered materials. Surprisingly, our results indicate that the magnitude of a vibrational modeâ€™s thermal conductivity correlates positively with how localized the mode is, which runs exactly counter to results in other disordered materials. We provide some hypotheses as to why this inversion may exist and suggest some approaches by which one may be able to alter the thermal properties of polymers in the future. We have furthermore observed the presence of modes with an imaginary frequency, which is unusual for a stable solid material. We make some simple observations about the nature of these modes and their contribution to thermal conductivity, finding that surprisingly, their contribution is significant given the small percentage of modes that fall into this category.