P. Nikitas, AGGREGATION PHENOMENA OCCURRING ON AN ELECTRODE SURFACE IN THE PRESENCE OR ABSENCE OF AGGREGATION IN THE BULK ELECTROLYTE SOLUTION, Journal of electroanalytical chemistry [1992], 425(1-2), 1997, pp. 97-106
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.