Authors:Iria Fraga, S. Montserrat, and J. Hutchinson
TOPEM is a new temperature modulated DSC technique, introduced by Mettler-Toledo
in late 2005, in which stochastic temperature modulations are superimposed
on the underlying rate of a conventional DSC scan. These modulations consist
of temperature pulses, of fixed magnitude and alternating sign, with random
durations within limits specified by the user. The resulting heat flow signal
is analysed by a parameter estimation method which yields a so-called ‘quasi-static’
specific heat capacity and a ‘dynamic’ specific heat capacity
over a range of frequencies. In a single scan it is thus possible to distinguish
frequency-dependent phenomena from frequency-independent phenomena. Its application
to the glass transition is examined here.
Authors:I. Fraga, S. Montserrat, and J. Hutchinson
The process of vitrification that occurs during the isothermal cure of a cross-linking system at temperatures below Tg∞, the glass transition temperature of the fully cured resin, has been studied by TOPEM, a new temperature modulated DSC (TMDSC)
technique based upon the use of stochastic temperature pulses. A comparison is made between TOPEM and another TMDSC technique,
and some advantages of TOPEM are considered. The TOPEM technique is used to show that the mobility factor is not always a
reliable approach to predicting the cure rate during vitrification, in view of its frequency dependence. Also, the dependence
of the apparent vitrification time on frequency is examined. There appears to be a non-linear relationship between the apparent
vitrification time and log(frequency), which is further discussed in the second part of this series.
Authors:I. Fraga, J. Hutchinson, and S. Montserrat
The processes of vitrification and devitrification that occur in an epoxy resin when it cures non-isothermally with a hardener
are studied in terms of their frequency dependence and as a function of the heating rate. A novel modulated DSC technique,
TOPEM, has been used which permits the evaluation of the frequency dependence for a single sample in a scan at constant underlying
heating rate, thus avoiding errors arising from the composition of the sample. The effects of both frequency and heating rate
on vitrification and devitrification are investigated. Some advantages of this technique are observed and discussed.