Thermodynamics of polystyrene solutions. Part 2.—Polystyrene and ethylbenzene

The volume change on mixing polystyrene with ethylbenzene has been determined directly at 25°C. It is negative and amounts to ca. 0.30 % of the total volume at ϕ2= 0.5. Osmotic pressures have been measured at 10°, 35°, and 60°C in the concentration range ϕ2= 0.09 to 0.27. The temperature coefficient of the reduced residual chemical potential χ is close to zero; hence the heat of dilution is very small. The entropy of dilution is positive but small. The statistical thermodynamic theory employed in the preceding paper accounts for the sign and magnitude of the excess volume. The experimental partial molar entropies are much smaller than the combinatory contribution alone would allow. This finding and the small negative enthalpy of dilution indicated by recent work of Palmen are shown to arise mainly from equation-of-state terms of the newer theory. The parameter X12 representing the exchange enthalpy is positive and small, as should be expected for this system. The observed increase in χ with concentration is well reproduced by the theory. Thermal expansivities and thermal pressure coefficients of ethylbenzene have been determined at atmospheric pressure from 10° to 90°C.