Shear-induced overaging in a polymer glass.

A phenomenon recently coined as overaging implies a slowdown in the collective (slow) relaxation modes of a glass when a transient shear strain is imposed. We are able to reproduce this behavior in simulations of a supercooled polymer melt by imposing instantaneous shear deformations. The increase in relaxation times Delta(tau(1/2)) rises rapidly with deformation, becoming exponential in the plastic regime, and is accompanied by significant changes in the distribution of these relaxation times throughout the system. This overaging is distinct from standard aging. We find increases in pressure, bond-orientational order, and in the average energy of the inherent structures (<e(IS)>) of the system, all dependent on the size of the deformation. The observed change in behavior from elastic to plastic deformation suggests a link to the physics of the "jammed state."