Simulation of a glass transition in a hot-wire experiment using time-dependent heat capacity

Abstract

The transient hot-wire method is used for simultaneous measurements of the thermal conductivity λ and the heat capacity per unit volumepc p and yields a peak in λ and a dip inpc p near a glass transition. Through simulations, it is shown that these anomalous results arise due to a time dependence inc p , which is described by a fractional exponential function:c p (t)=c p (liquid)+[c p (glass)-c p (liquid)c -(t,τ)β], where τ is the heat capacity relaxation time and β is a sample dependent parameter (0<β≤1). By a comparison with experimental data for cyclohexanol and glycerol, it is demonstrated that this model can be used to reproduce the peak and the dip as well as the temperature at which these occur. In addition, it is shown that the maximum in λ occurs at τ-0.3 s, whereas τ of the minimum inpc p is dependent on β and moves from 0.4 to 1 s for a change in β from 1 to 0.5. The difference in τ between the peak and the dip is in agreement with the experimental results. It is concluded that the anomalies reveal glass forming characteristics such as a rough classification in terms of strong and fragile glass formers.