Excess specific heats in miscible binary blends with specific interactions

Excess specific heats of different binary blends involving different levels of relatively strong specific interactions have been deter mined from spec ific heats of the pure components and those of the blends. A heat-flux (Cal vet) calorimeter and a step-by-step methodology have been used. Blends of p oly(hydroxy ether of bisphenol A) (phenoxy resin) with polyesters and polye thers, where specific interactions are supposed to play a role in miscibili ty, and blends with stronger hydrogen-bond interactions, such as poly(vinyl phenol)/poly(methyl methacrylate) (PVPh/PMMA), have been included in the s tudy. Only the experimental excess specific heat for the PVPh/PMMA blend is negative, whereas those relative to phenoxy blends are all positive. These results have been analyzed on the basis of an association model specifical ly designed for polymer blends in which miscibility is mainly caused by hyd rogen bonding. The model predicts, in all cases, a continuous decrease of t he enthalpy of mixing with temperature, i.e., a negative value of Delta C-p . Equation of state effects have been included in the theoretical simulatio ns, giving modified trends of the enthalpy of mixing with temperature in a more reasonable agreement with the experimental results.