Mixed aggregation processes at the electrified Hg-electrolyte solution interface. The case of sodium dodecylsulphate-tween 80(R), sodium dodecylsulphate-cetyltrimethylammonium bromide and tween 80(R)-cetyltrimethylammonium bromide co-adsorption

The formation and properties of mixed micellar-like films on the Hg electrode in the presence of two surfactants in the electrolyte solution is studied by means of differential capacity measurements. The experimental data are analysed on the basis of previous theoretical treatments. It is found that the system sodium dodecylsulphate-cetyltrimethylammonium bromide exhibits two different behaviours: At bulk solutions rich in sodium dodecylsulphate a film of mixed aggregates covers the electrode surface from positive polarizations up to -1.6V (see). In contrast, at bulk solutions rich in cetyltrimethylammonium bromide the electrode surface is covered with a bilayer of aggregates composed exclusively of cetyltrimethylammonium cations, which negative of -1.2 V (see) collapses to a condensed layer due to its penetration from dodecylsulphate anions. When the electrolyte solution contains sodium dodecylsulphate and tween, then under favourable conditions the electrode is covered with aggregates of pure dodecylsulphate anions from positive potentials up to the first capacitance peak at negative potentials. Negative of this peak and up to the second peak at far negative potentials the electrode is covered with mixed aggregates rich in tween. Finally, in the system of tween-cetyltrimethylammonium bromide the electrode is covered with a film of mixed aggregates, possibly of variable composition, throughout the range of potentials we studied. Copyright (C) 1996 Elsevier Science Ltd.