Solidity of viscous liquids. III. Alpha relaxation

TL;DR

This paper proposes that the universal high-frequency decay in viscous liquids' alpha relaxation is due to a negative long-time tail in stochastic dynamics, linked to the solidity of such liquids and their diffusion properties.

Contribution

It introduces a mechanism connecting the alpha relaxation decay to the solidity of viscous liquids and their diffusion constants, emphasizing the role of coherent diffusion.

Findings

High-frequency alpha loss decay follows an omega^{-1/2} pattern.

Coherent diffusion constant exceeds estimates based on alpha relaxation time.

Solidity of viscous liquids influences diffusion and relaxation behavior.

Abstract

It is suggested that the $\omega^{-1/2}$ high-frequency decay of the alpha loss in highly viscous liquids, which appears to be generic, is a manifestation of a negative long-time tail as typically encountered in stochastic dynamics. The proposed mechanism requires that the coherent diffusion constant is much larger than estimated from the alpha relaxation time. This is justified by reference to the solidity of viscous liquids in an argument which, by utilizing the irrelevance of momentum conservation at high viscosity and introducing a center of mass diffusion constant, implies that at high viscosity the coherent diffusion constant is much larger than the incoherent diffusion constant.