Surface defreezing of glasses

TL;DR

This paper investigates the phenomenon where glass surfaces flow below the bulk glass transition temperature, proposing a theoretical model for surface defreezing and its experimental implications.

Contribution

It introduces a theoretical framework for understanding surface defreezing in glasses, contrasting it with crystal surface melting, and discusses potential experimental detection methods.

Findings

Surface forms a liquid-like layer of thickness ~ -ln(T*-T) near T*

Integrated diffusivity across the interface remains finite as T approaches T*

Differences in shape due to surface and bulk flow could enable experimental detection

Abstract

A glass surface may still flow below the bulk glass transition temperature, where the underlying bulk is frozen. Assuming the existence at T=T* of a bulk thermodynamical glass transition, we show that the glass-vapor interface is generally wetted by a liquid layer of thickness ~ -ln(T*-T) when T--> T*. Contrary to standard surface melting of crystals however, the integrated value of the diffusivity across the interface remains finite for T-->T*. Difference in shape induced by bulk and by surface flow is discussed as a possible means of experimental detection of surface defreezing.