MIXED AGGREGATION PROCESSES AT THE ELECTRIFIED HG-ELECTROLYTE SOLUTION INTERFACE - THE CASE OF SODIUM DODECYL-SULFATE-TWEEN 80(R), SODIUM DODECYL-SULFATE-CETYLTRIMETHYLAMMONIUM BROMIDE AND TWEEN 80(R)-CETYLTRIMETHYLAMMONIUM BROMIDE COADSORPTION

The formation and properties of mixed micellar-like films on the Hg el ectrode in the presence of two surfactants in the electrolyte solution is studied by means of differential capacity measurements. The experi mental data are analysed on the basis of previous theoretical treatmen ts. It is found that the system sodium dodecylsulphate-cetyltrimethyla mmonium bromide exhibits two different behaviours: At bulk solutions r ich in sodium dodecylsulphate a film of mixed aggregates covers the el ectrode surface from positive polarizations up to -1.6V (see). In cont rast, at bulk solutions rich in cetyltrimethylammonium bromide the ele ctrode surface is covered with a bilayer of aggregates composed exclus ively of cetyltrimethylammonium cations, which negative of -1.2 V (see ) collapses to a condensed layer due to its penetration from dodecylsu lphate anions. When the electrolyte solution contains sodium dodecylsu lphate and tween, then under favourable conditions the electrode is co vered with aggregates of pure dodecylsulphate anions from positive pot entials up to the first capacitance peak at negative potentials. Negat ive 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 i s covered with a film of mixed aggregates, possibly of variable compos ition, throughout the range of potentials we studied. Copyright (C) 19 96 Elsevier Science Ltd.