Thermal expansivity of polystyrene determined by multi-frequency dilatometry

Abstract

Thermal expansibility and heat capacity of solids in general are linked by the first Grüneisen parameter. While the thermal expansion results from molecular motion in an anharminic potential, contribution to the heat capacity results from all kinds of motion. Similar to the temperature modulated DSC, thermal expansion can be measured by modulated temperature dilatometry (MT-DIL). One component corresponding to the reversing dilatation contributes to both the total and the modulated dimension change, while the non-reversing gives a characteristic easily distinguishable spike. In the present work a multi-frequency temperature modulated program was applied in push-rod dilatometer to measure a coefficient of thermal expansion (CTE) of polystyrene in the temperature range up to glass transition. At the temperature just below glass transition, the frequency dependence of CTE is observed, similar to the heat capacity behavior by MT-DSC.