Can we use area per surfactant as a quantitative test model of specific ion effects?

Abstract

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. © 2004 Elsevier Ltd. All rights reserved.