ABSTRACT
The frequency dependence of the coefficient of thermal expansion can be investigated in experiments in which a sinusoidal temperature load is applied. As a result, a complex coefficient of thermal expansion is obtained. In Figure 1 results are shown from an investigation of Bauer & Boehmer (2000) in which capacitive scanning dilatometry was employed. A thin film made of polystyrene was subjected to a harmonic temperature loading with an amplitude of less than 1 K at a frequency of 4 mHz in the temperature range depicted. While in the in-phase response α ′ a transition from a lower “glassy” value to a higher “relaxed” value occurs as the temperature is increased, the out-ofphase response α ″ runs through a maximum as the transition in α ′ occurs. Thus the results are similar to the ones obtained in a dynamic-mechanical analysis in which the storage and loss modulus are determined. Just as there exists a shift property in the mechanical case, by which the data obtained for one temperature can be related to that at another temperature by the well known time-temperature shift principle (Ferry 1980), the same is true for the thermal properties, as can be seen from Figure 2. Here, results from a harmonic experiment with
polybutadiene are depicted for two different frequencies of the sinusoidal temperature input.
