Excess heat capacities of glyme[ndash ]alkane mixtures Influence of the upper critical solution temperature

Abstract

Differential scanning calorimetry has been used to determine the excess heat capacity of liquid mixtures of triglyme and tetraglyme with cyclohexane, and tetraglyme with n-heptane, at 288.15, 298.15 and 308.15 K, at atmospheric pressure, throughout the composition range. The curves thus obtained as a function of composition were found to be W-shaped. The results are compared with those for other glyme–alkane mixtures. Changes in the W-shaped curves with temperature were virtually linear for mixtures which have an upper critical solution temperature (UCST) relatively distant from the measuring range; by contrast, excess heat capacities increased asymptotically near the phase separation region. The results are discussed in terms of order creation in the mixture that arises from concentration fluctuations near the UCST.