A molecular explanation of the transition from viscous to hopping mechanism of mass transport in the supercooled liquid near the glass transition

摘要: When the viscosity of a supercooled liquid becomes large, mechanism mass transport is known to undergo change from dependent, Stokes-Einstein behavior an activated hopping dominated, almost independent behavior. This occur rather sharply near temperature $T_c$ where mode coupling theory predicts singularities in properties liquid. However, origin this not well-understood. Here we suggest simple microscopic interpretation crossover. Our analysis based on scaled particle calculation activation energy for and non-Markovian rate barrier crossing. We find that as is-progressively supercooled, increases rapidly which makes curvature at top also increase. At high densities latter gives more dominant large scosities collective diffusion inefficient. The suddenness crossover because density increased, decreases increase energy, rapid required tilt balance favor mechanism. can only happen dynamic singularity undergoes sharp present offers explanation decoupling structural relaxation values latter-such has been suggested recently by Angell. provides tentative recent simulation results Keyes co-workers.