Effect of the molecular structure on the adsorption of alkyl ether sulphates and alkane ether sulphonates at the air-water interface

The adsorption properties of defined oxyethylated and non-oxyethylated sodi um alkane sulphonates [0-3 oxyethylene (EO) units] and sodium alkyl sulphat es (0-2 EO units) in aqueous solutions are sytematically studied. The adsor ption parameter values of these surfactants of high surface-chemical purity are calculated on the basis of Frumkin's adsorption isotherm. Defined chan ges of the chemical structure of oxyethylated anionics (sulphates, sulphona tes) affect the adsorption properties. The adsorption parameter data of the different surfactants are discussed with respect to the lattice structure available only for the non-oxyethylated sodium dodecyl sulphate and that wi th one EO unit. The molecular structures of all other surfactants investiga ted in this work are calculated by structure optimization using the semi-em pirical AMI method. Based on these data, the effect of the defined oxyethyl ation steps on the packing and intermolecular interactions within the adsor ption layer is critically discussed. (C) 1998 Elsevier Science B.V. All rig hts reserved.