A calorimetric study of structural relaxation in the glassy state of a liquid-crystal polymer

The physical ageing of a side-chain liquid-crystal polymer is investigated by means of differential scanning calorimetry, which allows one to follow the enthalpy relaxation of the glass. Measurements are performed for different thermal treatments and compared with the predictions of two phenomenological models where the nonlinearity of the ageing process is accounted for by multiparameter expressions. The experimental results can be described with the model based on the Narayanaswamy expression for nonlinearity. although it seems that the model based on the Hodge expression fits experimental data more satisfactorily. In particular, a single set of parameters is determined which describes different experiments. However, the value of the enthalpy loss as a function of the ageing time is greatly overestimated by both models.