Interfacial micellization of cetyl-dimethyl-benzylammonium chloride and Tween-80R at the Hg/electrolyte solution interphase

The adsorption of a cationic micelle—forming surfactant, cetyl—dimethyl-benzylammonium chloride, and of a neutral surfactant, Tween 80 R , from aqueous electrolyte solutions on a polarized mercury electrode was studied by means of differential capacitance measurements in order to examine the influence of the structure and charge of the adsorbate on interfacial micellization. For both surfactants, deformed capacitance peaks were recorded, accompanied by capacitance plateaux. These are sufficient criteria for the occurrence of a two- or three-dimensional aggregation process of the adsorbate molecules within the electrical double layer. The adsorption behaviour of cetyl-dimethyl-benzylammonium cations 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 favourable conditions at far negative or positive polarizations respectively. Since these adsorbates have quite different structures, these similarities are attributed to their ionic character. In contrast, the surface aggregates of Tween 80 R do not collapse to a compact layer but are stable over an extended potential range, forming two micellar plateaux. Finally, general conclusions of our theoretical and experimental studies on micellization at charged interphases are also presented.