Adsorption of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride on a hanging mercury electrode studied by adsorptive transfer stripping voltammetry

Abstract

The adsorption of cetyltrimethylammonium bromide (CTAB) and cetyldimethylbenzylammonium chloride (CDBACl) on a hanging mercury electrode is studied using adsorptive transfer stripping voltammetry. The surfactants are adsorbed on mercury and are then transferred in KBr or KCl under various conditions, including temperatures from 1 to 40°C, open or closed circuits with different initial potentials, and repeated scans, etc. The results are compared with previously published results on the adsorption of CTAB or CDBACl on mercury, where condensed films were formed and are quite different than those obtained by adsorptive stripping voltammetry. In this case, an absence of condensed film is observed for CTAB. A condensed film with low capacitance value is formed in the case of CDBACl after transfer at low temperatures, or after repeated scans, resulting in reorientation of the molecules to more compact states. Capacity time curves at the potentials where the film is formed show in a few cases a nucleation and growth mechanism, with induction time and studied by the Avrami formulation, while an observed increase of the capacitance with time is attributed to the formation of hemimicelles. The results also indicate the importance of interactions between the hydrophobic chains.