Heat capacity spectroscopy by using stochastic temperature modulated calorimetry: Time-temperature superposition and fictive temperature at the glass transition of poly (vinyl acetate)

Complex heat capacity spectra were measured by stochastic temperature modulated calorimetry using a conventional differential scanning calorimeter on poly (vinyl acetate) in the glass transition region during cooling. It is shown, that the real and imaginary part of the complex heat capacity spectra measured above and below vitrification can be scaled to a master curve by use of the frequency-temperature superposition principle. After the transition from a structurally equilibrated state to the non-equilibrated glass (vitrification), the shift factors deviate from the Vogel-Fulcher-Tammann-Hesse equation. The vitrification is described in the concept of fictive temperature using the Adam-Gibbs-Scherer equation for the temperature dependence of the relaxation time.