Regular Irregularity in the Transfer of Anionic Surfactant across the Liquid/Liquid Interface

Abstract

Irregular current spikes and other anomalies seen in voltammetry of the transfer of anionic surfactants, alkyl sulfonates, and alkyl sulfates across the 1,2-dichloroethane/water (DCE/W) interface are reproducible. The anomalies have a certain regularity that is predicted by a recently proposed concept, the electrochemical instability. Irregular current spikes follow after the augmentation of the current induced when the phase-boundary potential is brought close to the mid-point potential of the transferring surfactant ions. Potential-step chronoamperometry clearly demonstrates the presence of the instability window, that is, the potential region where the interface becomes unstable only in the limited range of the phase-boundary potential.

Voltammetric Manifestation of the Ultraslow Dynamics at the Interface between Water and an Ionic Liquid

“…This irregularity at the foot of the voltammograms is an indication that the potential-dependent adsorption and desorption of C 7 F 15 COO À induces irregular convective motion of the liquid phases adjacent to the interface, which is a typical phenomenon related to the electrochemical instability [84] seen at conventional liquid j liquid interfaces. [83,[85][86][87][88][89] The irregular current in Figure 4 exemplifies the electrochemical instability at the IL j W interface. It is interesting that this irregularity was not observed at higher scan rates; this fact may indicate that at higher scan rates, the structure of the interface is not at thermodynamic equilibrium, at which the electrochemical instability would develop.…”

Electrochemical Instability in Liquid–Liquid Two-Phase Systems

“…34,37,40,7988 A model based on the kinetics of ion-transfer, adsorption, and desorption reactions at the interface was proposed to explain the irregular current in a certain potential region on iontransfer voltammograms. 89 However, this model disagrees with the irregular current on the potential-step chronoamperogram for the transfer of surface-active ions, 82,83,86,88 since the model assumes the steady-state current when the potential is kept constant.…”

“…In the potential region where the irregularly increased current appears, the DCE«W interface is under the electrochemical instability condition; the potential region widens with an increase in the concentration of the surface-active ion but the location is independent of the concentration ( Figures 4A and 4B), 83,86,87 and the instability window determined by the voltammogram narrows with an increase in the concentration of the supporting electrolyte. 82 In addition, the increase in the scan rate causes the widening of the unstable potential region ( Figures 4B and 4C). 8183,86 Similar irregularly increased currents are reported for the transfers of octanoate, 79 alkylimidazoliums, 83 and complexes of alkaline earth ions with surface-active neutral ligands.…”

Diffusion within nanometric and micrometric spherical-type domains limited by nanometric ring or pore active interfaces. Part 1: conformal mapping approach

“…3(a). It is clear that this may apply to the case of dendrimers [21][22][23][24][25][26][27][28] or of oily droplets [17][18][19][20][21][22][23] but not to vesicles which are by definition spherical so that U = p/2. Nevertheless, to keep the largest generality to our analysis, we wish to examine in the following what happens when U may achieve any value (viz., 0 6 U 6 p) irrespective of the exact system considered.…”

“…This interface is described by a thin ring [20][21][22][23], presumably of a few molecules wide, whose cylindrical symmetry axis is the droplet radius perpendicular to the electrode surface. The ring width may even be statistically larger if instabilities of the triple interface due to ion transfer [24] or convectively induced movements [21] are involved. In this location, the electroactive material, the electrical potential and the counter-ions are all present.…”