A simple adsorption equation for adsorption of nonionic surfactants on hydrophilic surfaces of silica

Abstract

Using methods of statistical thermodynamics, simple equations were developed describing adsorption isotherms of non-ionic surfactants from water onto polar surfaces. Their derivation was based on some generally-accepted views on the adsorption mechanism in these systems. In particular, on the assumption that at increasing surfactant concentrations a change in the orientation of the primarily adsorbed molecules can take place. Effects of secondary adsorption are also taken into account. An extensive model investigation based on our simple equations yields all the types of experimental adsorption isotherms reported so far in literature. Equations were also tested against some more accurate experimental data, obtained recently in CNRS laboratory in Montpellier.