Lifetime of spatially heterogeneous dynamic domains in polystyrene melts

A photobleaching method is used to measure the rotational dynamics of tetracene and rubrene in polystyrene, and to determine the lifetime of spatially heterogeneous dynamic domains in the polystyrene matrix. It is possible to selectively photobleach subsets of probe molecules in more mobile environments and to measure the time required for the remaining slower-than-average probes to be redistributed into an equilibrium set of environments. For polystyrene, this exchange time is much longer than the α-relaxation time at temperatures very near T_g and exhibits a strong temperature dependence. These results are qualitatively consistent with previous studies on tetracene in supercooled o-terphenyl and indicate that the observation of long-lived heterogeneous dynamic domains at temperatures very near T_g is neither matrix nor probe specific.