Poly(ethoxy) anionic surfactants: micellization and adsorption at the solid/liquid interface

The properties of three surfactants of the nonylphenolpolyethoxy sulphate t ype with 4, 10 and 25 ethoxy units are studied both in solution and at the solid/aqueous solution interface. Critical micelle concentrations, adsorpti on isotherms (on silica, alumina and kaolinite), enthalpies of micellizatio n or adsorption, are determined in various conditions. As for many surfacta nt systems, the adsorption can be described on a large range of concentrati on by the formation of surface aggregates, which are probably close in natu re to bulk micelles. The possibility of adsorption is mainly driven by the intel action of the anionic group with the surface (when the latter owns po sitively charged sites), whereas the final structure at saturation is gover ned by the ethoxy chain length like for non-ionic surfactants. (C) 2001 Els evier Science B.V. All rights reserved.