Using Mw dependence of surface dynamics of glassy polymers to probe the length scale of free surface mobility

TL;DR

This study investigates how the surface mobility of glassy polystyrene varies with molecular weight, revealing different behaviors above and below the glass transition, and introduces a method to probe the length scale of surface mobility.

Contribution

It demonstrates the use of surface levelling experiments and the glassy thin film equation to analyze surface mobility dependence on molecular weight in glassy polymers.

Findings

Surface mobility varies with molecular weight.

Different dependencies observed above and below glass transition.

The method probes the length scale of surface mobility.

Abstract

We describe a series of surface levelling experiments in glassy polystyrene (PS) of varying molecular weight. The evolution through a mobile surface layer is described by the glassy thin film equation that was introduced and used in a previous work. Excellent agreement with the data is achieved, with surface mobility as the single free parameter. Different molecular-weight dependencies in mobility are then observed above and below the glass transition. The results are discussed in terms of surface-chain anchoring in the bulk matrix, and the length scale for surface mobility.