Surface and Bulk Relaxation of Vapour-Deposited Polystyrene Glasses

TL;DR

This study investigates the surface relaxation dynamics of vapour-deposited polystyrene glasses, revealing enhanced surface mobility compared to bulk, with implications for understanding glassy surface behavior near the glass transition.

Contribution

It provides a detailed analysis of surface and bulk relaxation in vapour-deposited polystyrene glasses, combining experimental measurements with numerical modeling to quantify surface mobility.

Findings

Surface relaxation follows capillary-driven power law.

Enhanced surface mobility compared to bulk.

Temperature-dependent relaxation times align with previous studies.

Abstract

We have studied the liquid-like response of the surface of vapour-deposited glassy films of polystyrene to the introduction of gold nanoparticles on the surface. The build-up of polymer material was measured as a function of time and temperature for both as-deposited films, as well as films that have been rejuvenated to become normal glasses cooled from the equilibrium liquid. The temporal evolution of the surface profile is well described by the characteristic power law of capillary-driven surface flows. In all cases, the surface evolution of the as-deposited films and the rejuvenated films are enhanced compared to bulk and are not easily distinguishable from each other. The temperature dependence of the measured relaxation times determined from the surface evolution is found to be quantitatively comparable to similar studies for high molecular weight spincast polystyrene. Comparisons to numerical solutions of the glassy thin film equation provide quantitative estimates of the surface mobility. For temperatures sufficiently close to the glass-transition temperature, particle embedding is also measured and used as a probe of bulk dynamics, and in particular bulk viscosity.