Professor Mark Ediger is supported by a grant from the Theoretical and Computational Chemistry Program to perform experimental characterizations of the glass transition in supercooled organic liquids such as o-terphenyl, glycerol and trinaphthylbenzene. Time resolved optical spectroscopy on dilute solutions of rigid probes will be used. Measurements of pattern photobleaching of the optical probes will be used to determine how the rotational and translational motions decouple near the glass transition temperature. These experiments are motivated by results from a number of laboratories which indicate that translational motion has a significantly weaker temperature dependence than rotational motion as the glass transition is approached. The extent to which decoupling is observed for probes of different sizes will clarify the nature of the cooperative motion in supercooled liquids. In the last 25 years, physical chemists have made significant progress in the molecular interpretation of the static and dynamic properties of the liquid state. The relationship between intermolecular potentials and liquid structure is now well understood, and the role that solvent friction plays in molecular reorientation and chemical reactions is also understood for liquids of low viscosity. Nevertheless, the properties of supercooled liquids, and the molecular motions which occur near the glass transition temperature, are still not well understood. The experiments being conducted by Ediger are designed to shed light on the anomalous rotational and translational motions which occur in viscous supercooled liquids in the region near the glass transition temperature.
