Experimental determination of the glass transition temperature in a very narrow temperature range by Temperature Modulated Optical Refractometry

Latest since the landmark studies of Kovacs and co-workers on the glass transition of polymers, it is clear that thermally induced volume changes are of central importance for the understanding of the nature of the glass transition. Due to the kinetic background of the canonical (thermal) glass transition, it does not seem possible to derive a well-defined glass transition temperature T_g based on susceptibilities such as the thermal volume expansion coefficient, \beta(T), being strongly coupled to the glass transition process. Therefore, in practice, T_g is for example defined via the inflection point of the step-like \beta(T) curve. In this publication, we propose to use a thermo-optical feature, preceding the glass transition in the high-temperature phase, to determine the glass transition temperature T_g of a model polymer in a rather narrow temperature interval.