Experimental Studies of the Liquid-Glass Transition

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9980370CumminsThis project investigates the dynamics of liquids in the vicinity of the liquid-glass transition and of solid glasses by laser light scattering spectroscopy. Recent theoretical and experimental research has shown that relaxation (or memory) functions in supercooled liquids exhibit complex behavior extending over many decades in frequency. Current research is directed at measuring these functions and their evolution with decreasing temperature. The data analysis will utilize an extension of mode coupling theory (MCT) that now includes orientational degrees of freedom. A systemic investigation of both polarized and depolarized Brillouin scattering in the molecular glass-former salol will be carried out to explore the extent to which relaxation functions can be determined reliably with this technique. They will be used to assess the compatibility of such results with MCT, which provides detailed predictions for density correlation functions and their evolution with temperature. In addition, the dynamics of glasses at lower temperatures where aging phenomena and two-time scaling behavior has been predicted theoretically and observed in computer simulations will be pursued. The techniques developed will also be applied to new materials including elastomers, materials in which the liquid and glass phases are separated by an intermediate elastomer (or rubber) phase.%%%The liquid-glass transition is one of the oldest unresolved fundamental problems in condensed matter physics. It is also of major practical concern in the manufacture of various glasses including plastics and glassy metallic alloys. Current mode coupling theories will be tested to assess the extent to which relaxation (or memory) functions can be determined reliably with this technique. In addition, the dynamics of glasses at lower temperatures where aging phenomena and two-time scaling behavior has been predicted theoretically and observed in computer simulations will be pursued. The techniques developed will also be applied to new materials including elastomers, materials in which the liquid and glass phases are separated by an intermediate elastomer (or rubber) phase.This research project utilizes laser light-scattering techniques and will be conducted by primarily by graduate students and postdoctoral researchers. The program will include collaborations with other research groups both in the US and in Europe.***