AGGREGATION PHENOMENA OCCURRING ON AN ELECTRODE SURFACE IN THE PRESENCE OR ABSENCE OF AGGREGATION IN THE BULK ELECTROLYTE SOLUTION

One single-step and two multi-step models for aggregation processes oc curring on an electrode surface in the presence or absence of aggregat ion phenomena in the bulk solution are used to study the properties of an adsorbed monolayer when the adsorbate molecules are able to form a ggregates. It is shown that, despite the fact that the three models pr edict considerable different size distributions of the intermediate ag gregates, they give almost the same picture about the composition of a n adsorbed monolayer and its capacitance characteristics. According to these models, the only indication of the occurrence of a surface aggr egation process in the capacitance plots is the appearance of asymmetr ic peaks with one vertical side. Bulk aggregates do not affect the sha pe of the capacitance curves. If they are large, they stabilize the co mposition of the adsorbed layer and the shape of the capacitance curve s remains unchanged with the increase in the surfactant concentration. If they are small, i.e. oligomers, their effect is to reduce the adso rbate concentration in the bulk solution. Finally, the discrepancies b etween theory and experiment are indicated and the possibility that ad sorbed bulk aggregates disintegrate very slowly on the electrode surfa ce is discussed.