The critical micelle concentration (cmc) of the nonionic surfactant C8E5 in D2O was measured at 30 °C and pressures up to 350 MPa using 1H-NMR chemical shifts. The cmc was found to increase with pressure up to approximately 150 MPa and then decrease at higher pressures. This characteristic pressure dependence is similar to that reported for several ionic surfactant solutions and is in quantitative agreement with the effect of pressure on the transfer of hydrocarbons from water into nonpolar solvents. We conclude, therefore, that the observed behavior is independent of the hydrophilic headgroup of the surfactant and that it reflects a pressure-induced destabilization of the hydrophobic micelle interior at low pressures and enhanced stabilization at high pressures.

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Raman spectroscopy was used to study the vibrational and reorientational dynamics of bulk and confined liquid methyl iodide. A set of five porous silica glasses with pore radii ranging from 15 to 38 Å was employed as the confining material. With decreasing pore size a decrease in the ν3 (C– I) vibrational correlation time and an increase in the molecular reorientational correlation time were found. It is noted that the two‐state fast‐exchange model is not applicable in Raman studies owing to slow diffusion of pore molecules compared with the Raman spectroscopic time‐scale. A phenomenological linear correlation between the correlation times and the reciprocal of the pore radius was found to be useful and employed for data analysis. A relatively low sensitivity of the reorientational dynamics of methyl iodide to confinement was explained by considering the shape and mass distribution of a methyl iodide molecule. Copyright © 2000 John Wiley & Sons, Ltd.

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