STRUCTURAL STUDIES OF AN ORGANIC LIQUID THROUGH THE GLASS-TRANSITION

We have performed neutron diffraction experiments on deuterated propyl ene glycol, an organic glass former, at temperatures ranging from wher e its dynamical response approaches that of normal liquids to below th e point where relaxation times appear to diverge. Our studies extend o ver a very broad range of scattering wave vector (0.01<Q<30 Angstrom(- 1)). In contrast to models which predict clustering, we find no eviden ce in the liquid at any temperature for heterogeneities large on molec ular scales. However, we do note subtle changes at shorter lengths. Us ing molecular dynamics simulations to model our results, we identify t hese changes with increasing density and increasing orientational orde r induced by hydrogen bonding in the liquid as it cools. Analysis of t he orientational correlations between molecules reveals a strong depen dence on their relative positions. (C) 1996 American Institute of Phys ics.