The thermo-optical coefficient as an alternative probe for the structural arrest of polymeric glass formers

Abstract

The most important, yet independent susceptibilities to characterize the canonical glass transition include the thermal expansion, the specific heat and the shear modulus. At the glass transition, all these susceptibilities show a step-like behaviour as a function of temperature. However, in principle, different susceptibilities provide different perspectives on the glass transition. Due to the effect of sample history and considerable kinetic influences on the thermal glass transition behaviour, the best way to evaluate these different perspectives is to investigate them simultaneously. In this publication, different perspectives on the dynamical freezing process are obtained by a single experimental method: Temperature-modulated optical refractometry (TMOR). TMOR is used to simultaneously investigate the dynamic thermal expansion and, indirectly, the shear viscosity of a model polymer, both contributing to the thermo-optical coefficient. It will be discussed how this thermo-optical property couples to the structural arrest designated as one of the characteristics of the solidification process of polymers.