COEXISTENCE CURVE OF POLYSTYRENE IN METHYLCYCLOHEXANE .1. RANGE OF SIMPLE SCALING AND CRITICAL EXPONENTS

We have measured coexistence curves for the system polystyrene- methylcyclohexane with varying molecular weight from Mw = 1.02×104 to 71.9×104. In the temperature range ε = (Tc - T)/Tc > 0.03, a deviation from simple scaling was observed for systems with Mw = 10.9∼71.9×104. The effect of correction terms on simple scaling was negligibly small for systems with M w = 1.02∼4.64×104. This finding is compatible with molecular weight dependence of a critical value of ε for the validity of the Landau theory. In the appropriate temperature range, where a contribution from the correction terms is negligible, an analysis by simple scaling gives the exponent β = 0.332±0.001 independent of molecular weight. The critical exponent for the diameter is also independent of molecular weight and determined as 0.858±0.005, which is consistent with results of recent specific heat measurements. © 1980 American Institute of Physics.