Dynamic heat capacity in the at relaxation process of poly(vinyl acetate) at low frequency

摘要

The segmental relaxation in poly(vinyl acetate) (PVAC has been studied through the determination of the isobaric dynamic heat capacity: C-p(*) (omega, T) = C-p(') (omega, T) - iC(p)(")(omega, T). The calorimetric measurements have been performed over a very low frequency range from 1 to 20 mHz using ac calorimetry. The real and imaginary parts of C-p(*) (omega, T) at constant frequency reflect the ot relaxation associated with the glass transition, but a low signal to noise ratio and/or some small unwanted contribution distorts the thermal behaviour of the imaginary component. In this work, we show that in order to estimate a suitable thermal dependence of the imaginary part an approximated method, tested before by means of dielectric relaxation spectroscopy (DRS) measurements, can be applied. A comparative analysis of the calculated effective relaxation time and the peak width has been performed with respect to the reported data, measured by both the specific heat spectroscopy (SHS) and modulated DSC (TMDSC) techniques, and DRS. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 37]