Influence of the nature of inorganic salts and their concentration on the simultaneous adsorption of cationic and anionic surfactants. Mixtures of dodecyltrimethylammonium salts with sodium hexylsulfate in the solutions containing the inorganic salt of ions common with the surfactants

Abstract

The influence of the nature of the inorganic ions (Cl −, Br −, and ClO 4 −) and of NaBr concentration on the process of simultaneous adsorption of the respective dodecyltrimethylammonium salts (chloride, bromide, and perchlorate) and sodium hexylsulfate at the free surface of solutions containing NaCl, NaBr, or NaClO 4, respectively, was studied. Inorganic anions and hexylsulfate anions were found to adsorb competitively at the surface of solutions containing dodecyltrimethylammonium cations, at sufficiently high concentrations of inorganic salts. A lyotropic series of the anions Cl −<Br −∠ClO 4 − was also found for the process of coadsorption. Specific interactions between ClO 4 − and dodecyltrimethylammonium cations resulted in relatively high values of the free enthalpy of dodecyltrimethylammonium perchlorate adsorption and in significant asymmetry of the surface of solutions containing dodecyltrimethylammonium perchlorate and sodium hexylsulfate. Observed effects were described using the Butler-type isotherm of adsorption. Parameters of the adsorption were within the range of the component concentrations studied. The components were practically independent of concentrations which makes the Butler-type isotherms of adsorption especially convenient for pragmatic reasons.