Atomistic simulation of aging and rejuvenation in glasses

Slow structural relaxation ("aging") observed in many atomic, molecular, and polymeric glasses substantially alters their stress-strain relations and can produce a distinctive yield point. Using Monte Carlo simulation for a binary Lennard-Jones mixture, we have observed these phenomena and their cooling-rate dependences for the first time in an atomistic model system. We also observe that aging effects can be reversed by plastic deformation ("rejuvenation"), whereby the system is expelled from the vicinity of deep minima in its potential energy surface.

Diversity in liquid supercooling and glass formation phenomena illustrated by a simple model

The opportunity to map condensed-phase inherent structures (potential energy minima) approximately onto the vertices of a high-dimensional hypercube provides simple conceptual and numerical modeling for first-order melting-freezing transitions, as well as for liquid supercooling and glass formation phenomena. That approach is illustrated here by examination of three interaction examples that were selected to demonstrate the diversity of thermodynamic behavior possible within this hypercube modeling technique. Two of the cases behave, respectively, as "strong" and "fragile" glass formers, at least as judged by their heat capacities. The third presents a "degenerate glass," wherein full equilibration of the supercooling liquid (i.e., no kinetic arrest) leads to (a) residual entropy in the limit of absolute zero temperature, and (b) a linear temperature dependence of heat capacity in the same limit. None of the three cases displays a positive-temperature ideal (intrinsic) glass transition.