The system sodium cholate (NaC) + β-cyclodextrin (β-CD) in water has been studied by speed of sound and density measurements to obtain the corresponding apparent and partial molar volumes and adiabatic compressibilities. For pure NaC the values for the micellization volumes and compressibilities have been obtained, as well as the transference properties due to the complexation for the ternary system. When the β-CD is present, a shift in the critical micelle concentration of the surfactant equivalent to the amount of β-CD added is observed, due to the complex formation between solutes that delays the micellization. At infinite dilution, there is a marked change in the compressibility of the surfactant, although it is not appreciable in the volume. A detailed molecular modeling study has been carried out to elucidate, together with 1 H NMR data, the microscopic structure of the complex.

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We have measured the equation of state surface for the mixtures poly(4-hydroxystyrene) + ethanol, and + tetrahydrofuran below 40 MPa. The results obey a superposition principle that makes it possible to build a master curve once the p-V-T surface is known at a given pressure. The master curve depends on a single system-dependent parameter that, for the two systems studied, takes almost the same value. The results have been analyzed with a lattice fluid model that includes the existence of hydrogen bonds. Even though the model describes the composition dependence of the excess volume, it underestimates the pressure dependence of the density. While the inclusion of hydrogen bonds in the model has a negligible influence on the predictions for the system with tetrahydrofuran, it improves significantly the predictions for the system with ethanol.

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