ADSORPTION OF SODIUM DODECYL-SULFATE ON MERCURY AS AN EXAMPLE OF MICELLIZATION WITHIN A MULTILAYER INTERPHASE

The adsorption of sodium dodecylsulphate from aqueous electrolytic sol utions on a polarized mercury electrode was studied by means of differ ential capacitance measurements over a wide range of concentration and potential, and in the presence of different supporting electrolytes w ith different ionic strengths. An interpretation of the differential c apacitance vs. applied potential curves is given, based on theoretical treatments developed previously. It is shown that at concentrations b elow the cmc, two-dimensional aggregates are formed on the electrode s urface within a polarization region which is bounded by two capacitanc e peaks at extreme positive and negative polarizations. This film is n ot particularly stable and is transformed into a compact layer at pola rizations close to the potential of maximum adsorption, resulting in a capacitance pit. With increasing bulk concentration the aggregation p rocess extends across the interphase and at least two layers of aggreg ates-micelles are formed at concentrations around and above the cmc. T his three-dimensional aggregation is characterized by the appearance o f deformed and/or split capacitance peaks which determine the polariza tion region where this phenomenon occurs.