DYNAMIC HETEROGENEITIES IN GLASSES AND MISCIBLE POLYMER BLENDS: COMPUTER SIMULATIONS USING THE BOND FLUCTUATION MODEL

Open Access
Author:
Kamath, Sudesh
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 13, 2002
Committee Members:
  • Sanat K Kumar, Committee Chair
  • Ralph H Colby, Committee Member
  • Jayanth R Banavar, Committee Member
  • Evangelos Manias, Committee Member
Keywords:
  • simulations
  • glass transition
  • Polymer Blends
  • bond fluctuation model.
Abstract:
While the glass transition has been the subject of a considerable amount of research over the past few decades, it is still an unsolved problem in condensed matter physics and there is considerable debate about the exact nature of the glass transition. While some theories invoke a thermodynamic transition associated with the glass transition, others attribute the glass transition to structural arrest that is purely kinetic in nature. The objective of this thesis is to obtain a better understanding of the glass transition phenomenon and probe the thermodynamics of a glass-forming system to search for evidence of a thermodynamic signature to the onset of glassy behavior. We also make an attempt to relate the length-scale of dynamic heterogeneity in glass forming systems with the configurational entropy as predicted by the Adam-Gibbs theory. Miscible polymer blends have been the focus of intense research in recent years. Although these blends are thermodynamically miscible, they exhibit dynamic heterogeneity. While some theories attribute this phenomenon to concentration fluctuations and chain connectivity effects, others have argued that thermorheological complexity extit{only} reflects inherent differences in the local dynamics of the constituents. Moreover, there is no clear data on the molecular origins of dynamic heterogeneity. The objective of this thesis is to selectively probe the effects of each factor, namely concentration fluctuations and difference in inherent mobilities, on the dynamics of the two components in the blend and thus delineate their relative importance.