Utilization of “q+/q− = const.” DSC cycles for physical aging studies

Abstract

The utilization of the constant ratio cyclic temperature history, where q+/q−=const., was examined with respect to physical aging studies. In particular, determination of the apparent activation energy of enthalpy relaxation from constant ratio (CR) cycles was discussed. A novel equation fully utilizing the advantages of CR cycles was derived – it is based on shift of temperature corresponding to the maximum of relaxation peak Tp with the applied heating rate: −Δh*/R=dln(q+)/dTp−1. The equation was extensively tested for all types of structural relaxation behavior; it was proven to be highly accurate and independent from most data-distortive effects. In addition, it was shown that the unique shape of CR cycles curves can be utilized for the identification of certain data-distortive effects – thermal lags, imprecise heating/cooling rates or incomplete achievement of a true glassy state during cooling. Correspondingly, corrections for these data-distortive effects can be applied to other physical aging measurements performed for the given glassy material and DSC instrument.