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|Title:||Thermodynamics of polymerization, dielectric properties, and a new orientational glass|
|Department:||Materials Science and Engineering|
|Keywords:||Materials Science and Engineering;Materials Science and Engineering|
|Abstract:||<p>Five aspects of disordered solids and polymers have been studied, as follows. (1) The temperature and pressure modulation effects on structural relaxation have been formulated and simulated. The calculated heat capacity for the modulated conditions shows extra features over that for unmodulated conditions, which may cause misinterpretation of a disordered solid's characteristics. (2) A new mean field approximation in the lattice-hole model is developed for monodispersed polymer chains. Calculations of the configurational entropy, Sconf for polydispersed chains, has led to two predictions, (i) a maximum in the plot of configurational heat capacity against the extent of polymerization, and (ii) S conf remaining positive at 0 K. Both predictions have been verified by others. The lattice occupancy density contribution to S conf has been related to a liquid's viscosity and divergence of the viscosity-pressure plots explained. (3) From calorimetry and x-ray diffraction studies, a new phase of CuCN, which remains metastable on cooling to 77 K, has been discovered. It shows features characteristic of glasses. Sconf of this phase has been, calculated by using a flexible chain model. (4) A calorimetric method for determining the transition from mass-controlled to diffusion-controlled reaction kinetics during polymerization has been developed, and verified by experiments. In this transition range, the plot of the reaction rate against the reciprocal temperature at fixed value of the extent of polymerization deviates from the Arrhenius behavior. (5) Dielectric studies of linear chain polymerization of a melt in real time, and the polymers ultimately formed have shown that their properties depend upon the thermal history. This is attributed to different molecular level structures, e.g., chains and loops formed under different polymerization conditions. Altogether these theoretical and experimental studies have a broader consequence for our current understanding of the nature of disordered solids and of their formation from liquids, both molecular and polymeric.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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