No abstract

The adsorption process of cetyltrimethylammonium ion (CTA ϩ ) was studied as a function of the applied potential from interfacial tension ͑␥͒, differential capacitance ͑C͒ measurements, and both potentiostatic current ͓I ϭ I(t)͔ and capacity ͓C ϭ C(t)͔ transients obtained in the system Hg/0.1 M NaCl ͑aq) , x mM CTAB ͑aq) with x ͓5.02 ϫ 10 Ϫ3 , 1.60͔. From the surface excess concentration it was estimated that the surface area covered by the polar group of the surfactant is 86 Å 2 . During this CTA ϩ condensation process, two main stages could be distinguished, namely, short time scale stage ͑e.g., 1 ms͒ and the long time scale stage ͑e.g., 500 s͒. From the chronoamperometric study, it was possible to establish that during the former stage, the formation of an adlayer of perpendicular molecules of surfactant onto the electrode surface involves a mechanism where Langmuir-type adsorption and two-dimensional instantaneous nucleation occur simultaneously. Moreover, from the analysis of the experimental capacitance-time transients, the mechanism of the latter stage could be assessed: during this second stage the previously formed adlayer of amphiphile molecules is converted into strips of hemimicelles with an anion-induced hemicylindrical geometry through a one-dimensional instantaneous nucleation process.