INTERFACIAL MICELLIZATION OF CETYL-DIMETHYL-BENZYLAMMONIUM CHLORIDE AND TWEEN-80(R) AT THE HG ELECTROLYTE SOLUTION INTERPHASE/

The adsorption of a cationic micelle-forming surfactant, cetyl-dimethy l-benzylammonium chloride, and of a neutral surfactant, Tween 80R, fro m aqueous electrolyte solutions on a polarized mercury electrode was s tudied by means of differential capacitance measurements in order to e xamine the influence of the structure and charge of the adsorbate on i nterfacial micellization. For both surfactants, deformed capacitance p eaks were recorded, accompanied by capacitance plateaux. These are suf ficient criteria for the occurrence of a two- or three-dimensional agg regation process of the adsorbate molecules within the electrical doub le layer. The adsorption behaviour of cetyl-dimethyl-benzylammonium ca tions shows striking similarities with that of sodium dodecylsulphate. Their aggregates on the electrode surface collapse to a compact layer at potentials negative of the ecm and a polylayer is formed under fav ourable conditions at far negative or positive polarizations respectiv ely. Since these adsorbates have quite different structures, these sim ilarities are attributed to their ionic character. In contrast, the su rface aggregates of Tween 80R do not collapse to a compact layer but a re stable over an extended potential range, forming two micellar plate aux. Finally, general conclusions of our theoretical and experimental studies on micellization at charged interphases are also presented.