THE APPLICATION OF MODULATED DIFFERENTIAL SCANNING CALORIMETRY TO THEGLASS-TRANSITION OF POLYMERS .1. A SINGLE-PARAMETER THEORETICAL-MODELAND ITS PREDICTIONS
Jm. Hutchinson et S. Montserrat, THE APPLICATION OF MODULATED DIFFERENTIAL SCANNING CALORIMETRY TO THEGLASS-TRANSITION OF POLYMERS .1. A SINGLE-PARAMETER THEORETICAL-MODELAND ITS PREDICTIONS, Thermochimica acta, 286(2), 1996, pp. 263-296
A single relaxation time model describing the kinetics of enthalpy rel
axation has been applied to modulated differential scanning calorimetr
y (MDSC) in the glass transition region. The model is able to describe
semi-quantitatively all the characteristic features of MDSC: the aver
age or total heat capacity which is very similar to the conventional D
SC response at the same average heating rate; a phase angle between he
ating rate and heat flow modulations which passes through a maximum in
the transition region; a ''loss heat capacity'' which shows a similar
behaviour to the phase angle; and a ''storage heat capacity'' which s
hows a sigmoidal change from glassy to liquid-like C-p. The model is u
sed to predict the effects of the experimental and material parameters
. Of the experimental parameters, the most important are the average h
eating rate and the period. The former affects significantly only the
total heat capacity, and in the same way as in conventional DSC. The l
atter affects significantly only the storage heat capacity, causing th
e sigmoidal transition to shift to higher temperatures as the period i
s reduced. The amplitude of temperature modulation appears to have no
significant effect within a reasonable range. These predictions, and t
hose for the effects of some material parameters, namely the initial e
nthalpic state and the non-linearity parameter, are discussed in the l
ight of published experimental data.