Response of glassy liquids to thermal gradients

The Soret effect, i.e., the flow of matter caused by a temperature gradient, is studied in a glass-forming binary Lennard-Jones (LJ) mixture, using nonequilibrium molecular dynamics computer simulation. The transport processes associated with this effect are thermal diffusion and interdiffusion. While interdiffusion processes exhibit a drastic slowing down when approaching the glass transition, thermal diffusion appears to be a fast process even in the glass. We show that the Soret effect becomes more pronounced in the vicinity of the glass transition, due to the decoupling between thermal diffusion and interdiffusion as well as the chemical ordering in the considered LJ mixture. This is reflected in the occurrence of large concentration gradients, nonlinear concentration profiles, and long-lived nonstationary structures.