A Spin-Probe Study of the Modification of the Hydration of SDS Micelles by Insertion of Sugar-Based Nonionic Surfactant Molecules

The spin-probe detected polarity index H (25 °C) of SDS micelles decreases linearly with the number of inserted sugar-based nonionic surfactant molecules. This decrease is interpreted as being due to the expulsion of water molecules by the sugar groups from the polar shell surrounding the hydrocarbon core of the dodecyl micelle. Employing the geometrical model described in the companion paper immediately preceding this work, the effective volume of water expulsion is found to be similar to the volume of the sugar groups after taking into account that the OH bonds of the sugar groups also contribute to the polarity index H (25 °C). The estimate of the hydration of pure SDS micelles as a function of their aggregation number from these studies with the spin probe 16 doxylstearic acid methyl ester is similar to that with 5 doxylstearic acid methyl ester. This confirms that both spin probes are located similarly in the polar shell.