Temperature modulated optical refractometry: A quasi-isothermal method to determine the dynamic volume expansion coefficient

The volume expansion coefficient is a thermodynamic key parameter yielding insight into molecular cohesion and organization of condensed matter. We present here the novel experimental technique temperature modulated optical refractometry (TMOR) to determine not only the static but also the dynamic volume expansion coefficient of transparent condensed matter of cubic or isotropic symmetry. A specialty of TMOR is its capability to measure the volume expansion coefficient under quasi-isothermal conditions. In this experimental mode TMOR is able to differentiate between static, dynamic and kinetic contributions to the volume expansion coefficient. Due to these features TMOR especially qualifies for the investigation of structural changes provoked by structural phase transitions, glass transitions and other structure-related transformations in transparent condensed matter. The scientific potential of this novel experimental technique is demonstrated by evidencing anomalies of the complex volume expansion coefficient accompanying the chemically induced glass transition occurring during the formation of a covalently cross-linked epoxy network.

► Novel technique temperature modulated optical refractometry. ► Quasi-isothermal measurement of the complex thermo-optic coefficient. ► Quasi-isothermal measurement of the complex coefficient of thermal expansion. ► Evolution of the volume expansion coefficient during the cure of an epoxy. ► Complex thermal expansion coefficient at a chemically induced glass transition.