Solvent distribution in non-ionic surfactant monolayers

Abstract

The distribution of solvent in the adsorbed monolayers of the non-ionic surfactants monododecyl hexaethylene glycol, C₁₂E₆, and monododecyl octaethylene glycol, C₁₂E₈, at the air–water interface has been determined from specular neutron reflectivity measurements. The data is analysed by the method of partial structure factors, and the solvent distribution is described by a new approach that improves previous estimates based on a tanh profile. An improved description and quantification of hydration in surface adsorbed layers is required for the further development of the thermodynamic treatment of surfactant mixing at interfaces. It is a term currently neglected in theories based on the pseudo phase approximation. However, the comparison of some recent neutron reflectivity results and surface tension data for mixed surfactants suggests that its contribution may be important.