RELAXATION OF SPATIALLY HETEROGENEOUS DYNAMIC DOMAINS IN SUPERCOOLED ORTHO-TERPHENYL

A photobleaching technique has been used to observe rotational dynamic s of dilute probe molecules in supercooled o-terphenyl (OTP). The none xponential rotational relaxation of the probe molecules is shown to be due, at least in part, to the presence of spatial heterogeneity in th e host dynamics. Under appropriate photobleaching conditions, a nonequ ilibrium distribution of probe molecule mobilities can be created by p referentially bleaching the more mobile probe molecules in a sample. N ear T-g this nonequilibrium distribution is observed to return to an e quilibrium distribution of relaxation times over times on the order of 10(3) tau(c), where tau(c) is the average rotational correlation time of a probe molecule. The time required to return to equilibrium is in terpreted as a structural relaxation time for dynamic heterogeneities in OTP. (C) 1995 American Institute of Physics.