Relaxation kinetics of nanoscale indents in a polymer glass

Nanometer scale indents have been written in a cross-linked polystyrene sample, and their relaxation has been studied at annealing temperatures well below the glass transition of the polymer. The indents represent a highly nonequilibrium state of the polymer which is subjected to mechanical stress of up to 0.4 GPa and thermal quench rates on the order of 108K/s during writing. It is shown that the relaxation towards equilibrium evolves logarithmically over more than 10 orders of magnitude in time. The relaxation kinetics are accurately described in terms of a thermally activated process with an energy barrier whose magnitude decreases linearly with the distance from equilibrium. © 2009 The American Physical Society.