2012/02/01 by J. S. Langer, Langer, J. S. · 1 citation
Materials Science · Physics and Astronomy · #Material Dynamics and Properties #Theoretical and Computational Physics #Liquid Crystal Research Advancements
paper · pdf · doi:10.48550/arxiv.1202.0086
The shear-transformation-zone (STZ) theory has been remarkably successful in accounting for broadly peaked, frequency-dependent, viscoelastic responses of amorphous systems near their glass temperatures Tg. This success is based on the theory's first-principles prediction of a wide range of internal STZ transition rates. Here, I show that the STZ rate-distribution causes the Newtonian viscosity to be strongly temperature dependent; and I propose that it is this temperature dependence, rather than any heterogeneity-induced enhancement of diffusion, that is responsible for Stokes-Einstein violations near Tg. I also show that stretched-exponential relaxation of density fluctuations emerges naturally from the same distribution of STZ transition rates that predicts the viscoelastic behavior. To be consistent with observations of Fickian diffusion near Tg, however, an STZ-based diffusion theory somehow must include the cascades of correlated displacement events that are seen in low-temperature numerical simulations.