The Adsorption and Condensed Film Formation of Cetyltrimethylammonium Bromide at the Mercury/Electrolyte Interface

The adsorption of cetyltrimethyammonium bromide (CTAB) on a hanging mercury electrode is studied in various electrolyte systems and temperatures. A condensed film is formed at negative potentials and at room temperature only in the presence of KBr. The decrease of the temperature favors the formation of the condensed film. Hysterisis phenomena are observed during the potential scans at both directions. Capacity time curves at the potentials where the film is formed show a nucleation and growth mechanism, with induction time depending on potential, which has been investigated using Avrami formulation and has been explained as a progressive one-dimensional nucleation with constant growth rate. The nucleation rate increases while moving toward more negative potentials. A linear decrease of the capacitance with time was observed in some cases independent of the measuring potential in a relative large potential range. The different types of micelles can affect the adsorption of CTAB on mercury. An unusual capacitance transient observed at a very narrow negative potential range is attributed to the formation of hemicylinders. The condensed film in the presence of the other electrolytes is observed only at high concentrations (1 M) and very low temperatures (5°C).