Coexistence curve of polystyrene in methylcyclohexane. I. Range of simple scaling and critical exponents

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Abstract
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 Mw=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.