Hydrophobic hydration and hydrophobic interaction in aqueous solutions of tert-butyl alcohol and trimethylamine-N-oxide: a correlation with the effect of these two solutes on the micellization process

Abstract

We report the study of the effect of tert-butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO) on a typical process governed by the hydrophobic interaction, such as the micellization of a surfactant in aqueous solution. The behaviour of the critical micelle concentration (c.m.c.) of the sodium dodecyl sulfate (SDS) was investigated as a function of the added amounts of TBA or TMAO by conductivity measurements. The hydration properties of the two solutes was studied by IR spectroscopy, in the region of the frequency of the O–H stretching band for H₂O and of the methylic band for TBA and TMAO. The overall behaviour of the TBA/H₂O and TMAO/H₂O solutions is also studied by compressibility measurements. The data were discussed in terms of the hydration properties of TBA and TMAO and of the thermodynamical properties of the mixtures. Significant correlations between these properties and the effect of TBA and TMAO on the micellization process are shown.