Thermal volume expansion as seen by Temperature-modulated optical refractometry, Oscillating dilatometry and Thermo-mechanical analysis

This paper revisits the experimental assessment of the thermal volume expansion behaviour via the novel technique of Temperature -modulated optical refractometry (TMOR) and compares it to two classical dilatometry techniques: Oscillating dilatometry (OD) and Thermo -mechanical analysis (TMA). This is done at the example of a model liquid (n-tetradecane, C14H30) and a homogeneous and isotropic, cross -linked epoxy thermoset in the viscoelastic state. It is shown that the thermal volume expansion coefficients of C14H30 obtained via TMOR and OD agree exceptionally well with each other and indeed reflect thermodynamic constants, if certain experimental boundary conditions are met. In the case of TMA analyses of the epoxy thermoset, the measured data was found to be biased rather easily, especially due to the tracking force that induces additional shape changes beyond thermal expansion. The controlled combination of TMOR and TMA allows differentiating between a "true" thermal volume expansion behaviour and additional shape changing effects.