Coexistence curve of polystyrene in methylcyclohexane. II. Comparison of coexistence curves observed and calculated from classical free energy

Abstract

Comparison of coexistence curves observed and calculated from the classical free energy was made for the systems polystyrene–methylcyclohexane and polystyrene–cyclohexane. Classical free energy was determined from the molecular weight dependence of the critical point. At low molecular weight, the numerically calculated coexistence curve was well represented by the leading term with the exponent β=1/2. The shape of the calculated coexistence curve is very different from the observed one because of the comparable values of the coefficient and different values of the exponent β observed and calculated. At high molecular weight, the entire shape of the observed coexistence curve is fairly well described by the calculated one. This fair description was caused by the large value of the calculated coefficient compared with the observed one and the narrow range of simple scaling. The numerically calculated coexistence curve was found to deviate from the leading term with β=1/2 at high molecular weight. Both in diameter and concentration difference, a transition from the critical region to the classical region was observed for the system polystyrene–cyclohexane with molecular weight Mw=156×104.