Dynamic specific heat of a supercooled liquid

Abstract

The dynamic specific heat Cp(ν) and thermal conductivity, κ, of the simple glass-forming liquid di-n-butylphthalate are measured over a wide frequency range (4 mHz–8 kHz) by a nonadiabatic ac technique due to Birge and Nagel. The relaxation frequency obtained from the specific heat is found to be non-Arrhenius down to the lowest temperatures attained in this measurement. The temperature dependence of the relaxation frequency is in close agreement with that obtained from shear modulus and dielectric susceptibility measurements indicating that all motions in the supercooled liquid are strongly coupled to one another. The shape of the relaxation spectrum changes with temperature. The width of the relaxation is similar to that of the dynamic specific heat of other supercooled liquids. The thermal conductivity is frequency independent through the calorimetric glass transition. The static specific heat is reported over a wide range in temperature extending up to 100 K above the melting point. No evidence is found for thermodynamic anomalies accompanying the proposed formation of spatial inhomogeneities in the liquid. The high frequency relaxation shape exhibits a power law which crosses over to a weaker frequency dependence as seen in the dielectric response.