Investigation of the effect of dimethyl sulfoxide and diethyl sulfoxide on sodium dodecyl sulfate micellization in aqueous solutions by fluorescence method

The effect of dimethyl sulfoxide (DMSO) and diethyl sulfoxide (DESO) on micellization of sodium dodecyl sulfate in aqueous solutions is studied by fluorescence method using pyrene as a luminescence probe. The critical micellization concentration of the surfactant is found to increase upon the addition of DMSO and DESO. The aggregation numbers and radii of micelles, the hydrophilic group area, and the parameters of critical compaction of micelles are calculated from the data on fluorescence quenching by hexadecylpyridinium bromide. It is shown that the dependence of the aforementioned parameters on the content of DMSO, unlike DESO, is linear throughout the studied concentration range. It is assumed that, in DMSO solutions, polarization effects always prevail, whereas, at low concentrations of DESO, changes in water structure and the interactions of ethyl groups with hydrocarbon chains of sodium dodecyl sulfate also play a significant role.