A spin-probe study of the modification of the hydration of SDS micelles byinsertion of sugar-based nonionic surfactant molecules

The spin-probe detected polarity index H(25 degrees C) of SDS micelles decr eases linearly with the number of inserted sugar-based nonionic surfactant molecules. This decrease is interpreted as bring due to the expulsion of wa ter molecules by the sugar groups from the polar shell surrounding the hydr ocarbon core of the dodecyl micelle. Employing the geometrical model descri bed in the companion paper immediately preceding this work, the effective v olume 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 11(25 degrees C). The estimate of the hyd ration of pure SDS micelles as a function of their aggregation number from these studies with the spin probe 16 doxylstearic acid methyl ester is simi lar to that with 5 doxylstearic acid methyl ester. This confirms that both spin probes are located similarly in the polar shell.