A sodium-specific condensed film of α-cyclodextrin at the mercury∣water interface

Effect of the deaeration on the adsorption of some cationic surfactants at the mercury/electrolyte solution interface

The effect of the deaeration on the adsorption of three cationic surfactants cetyldimethylbenzylammonium chloride (CDBACl), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB) at the mercury/electrolyte solution interface is studied. The deaeration is studied using either nitrogen or helium and the effect of deaeration process and time is also studied. In all cases an effect of the deaeration time is found which is mainly observed at potentials where a condensed film is formed. Capacity-time curves at the potentials where the film is formed show a nucleation and growth mechanism with induction time that depends on the deaeration time. The deaeration slows down the kinetics of the film formation but does not change the equilibrium capacitance value of the film. The decrease of the dissolved gas from the water that perturbs its structure is perhaps the main reason for the behaviour observed during the adsorption of these surfactants.

On the adsorption of cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface

The adsorption of cetyldimethylbenzylammonium chloride (CDBACl) on the hanging mercury electrode is studied in various supporting electrolytes at various temperatures from 1 to 50 degrees C. A condensed film with low capacitance is formed at negative potentials at transition temperatures below approximately 40 degrees C. The decrease of the temperature favors the film formation, and increases the width of the capacitance pit, while its value remains practically constant. Hysteresis phenomena are also observed during different scan directions. Capacitance-time curves at the potentials where the film is formed show in some cases a nucleation and growth mechanism with induction time and studied by the Avrami formulation. At high temperatures an increase of the capacitance with time is observed depending on the CDBACl concentration and slightly on the electrolyte used, and is attributed to the formation of hemimicelles. At high negative potentials a second narrow region with lower capacitance values is observed. This is easily observed at very high temperatures, while it is absent at lower temperatures. It depends upon the concentration of CDBACl and the electrolyte used. The results are different from those obtained for the adsorption of cetyltrimethylammonium bromide on mercury, indicating the importance of interaction between the hydrophobic chains.

On the adsorption and condensed film formation of dodecyl-, tetradecyl-, hexadecyl-, and octadecyltrimethylammonium bromides at the mercury/electrolyte interface

The adsorption and condensed film formation of dodecyl (DTAB)-, tetradecyl (TTAB)-, hexadecyl (CTAB)-, and octadecyl (OTAB)-trimethylammonium bromides on the hanging mercury electrode is studied in KBr as supporting electrolyte, at various temperatures from 5 to 45 degrees C. A condensed film is formed at negative potentials and at room temperature only in the presence of CTAB. The decrease of the temperature favors the formation of the condensed film. A transition temperature is observed for the film formation. Capacity-time curves at the potentials where the film is formed show a nucleation and growth mechanism, with induction time depending not only on the final potential but also on the initial potential range, although it is in the desorption region. In this temperature range no film is observed for DTAB and TTAB. However, the film is observed for OTAB, but only at higher temperatures, and is more easily formed with increasing temperature. The film is formed in a certain potential region and the nucleation rate increases while moving toward more negative potentials. Hysteresis phenomena are observed during changes of scan direction. The capacity vs time curves for OTAB, where condensed film is formed, are treated using an Avrami plot formulation and have been explained as progressive one-dimensional nucleation with a decrease of the nucleation rate during the overall film formation. The results show a marked effect of the chain length of the alkyl chain on the film formation.

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 degrees C).