Measurement of the Limiting Fictive Temperature over Five Decades of Cooling and Heating Rates

The fictive temperature (T-f) was defined by Tool in the 1940s as a measure of glassy structure. Tf is generally measured on heating and can be calculated from the enthalpy overshoot in calorimetric studies using a method developed by Moynihan. Prior work has demonstrated that the limiting fictive temperature (T-f') is similar to T-g (measured on cooling) and depends on the cooling rate in a manner consistent with the Williams-Landel-Ferry (WLF) relationship. Theoretically, the limiting fictive temperature should not depend on heating rate, but this has been experimentally verified only for a very limited range of heating rates. Here, rapid-scanning chip calorimetry and conventional differential scanning calorimetry (DSC) are combined to investigate T-f' for polystyrene over a broad range of heating rates ranging from 0.017 to 3000 K/s after cooling at different rates. The results show that T-f' depends on cooling rate following the WLF equation. On the other hand, T-f' is not a funct