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Surfactant film rigidity is a ubiquitous general concept that is quantified into two different units. We show here how to convert the bending rigidity from reduced units of a virtual infinitely thin film (not made of molecules) into the chemical unit (kJ.mol−1) of a realistic film of monomolecular thickness. In most cases, molecular lengths are not negligible versus curvature radius. Two bending constants for the elasticity of thin-shelled solids can be defined, as introduced by Gauss, whereas only one physical bending constant taking into account that the film cannot be torn has been introduced in the 1990s by Hyde and Ninham. The explicit conversion depends on the topology and is different in the quasi-planar approximation, as well as the 'direct' oil in water (o/w) or 'reverse' water in oil (w/o) case of spherical or cylindrical micelles. We show some examples for classical and nonclassical micelles and microemulsions of different compositions. Image 1 [ABSTRACT FROM AUTHOR]

The three main currently proposed approaches for understanding specific ion effects are briefly described. In some experimentally well defined and simplified situations, one can decouple ion specificity effects from all others. Small globular micelles in water/salt mixtures are one of the simple situations where specific ion effects can be distinguished: ‘hydrophobic ions’ introduced by Hofmeister in the late 19th century, also called ‘structure breaking’ or ‘salting in’ ions, which are similar to ‘soft ions’ in the classification introduced by Pearson, are more strongly adsorbed on the micellar surface than predicted by electrostatics alone. Hence, lateral repulsions between surfactants are increased, resulting in a measurable and calculable decrease of micelle size when adsorbing anions such as bromide replace non-adsorbing anions such as chloride. [Copyright &y& Elsevier]