Space charge limited release of charged inverse micelles in non-polar liquids

Abstract

Charged inverse micelles (CIMs) generated during a continuous polarizing voltage between electrodes in the model system of polyisobutylene succinimide in dodecane do not populate a diffuse double layer like CIMs present in equilibrium (regular CIMs), but instead end up in interface layers. When the applied voltage is reversed abruptly after a continuous polarizing voltage step, two peaks are observed in the transient current. The first peak is due to the release of regular CIMs from the diffuse double layers formed during the polarizing voltage step, which is understood on the basis of the Poisson-Nernst-Planck equations. The second peak is due to the release of a small fraction of generated negative CIMs from the interface layer. A model based on space charge limited release of the generated negative CIMs from the interface layer is presented and the results of the model are compared with several types of measurements. For the situation in which the bulk is deprived of regular CIMs and neutral inverse micelles, the results of the model are in agreement with the experimental results.However, for the situation in which regular CIMs and neutral inverse micelles are present, the 2 model shows discrepancies with the experiment for high voltages and high charge contents.These discrepancies are attributed to electrohydrodynamic flow caused by local variations in the electric field at the vicinity of the electrodes, which occur during the reversal voltage.Also the long term decrease of the amount of released generated CIMs is studied and it is found that the presence of regular CIMs and neutral inverse micelles speeds up the decrease.This study provides a deeper insight in the electrodynamics of CIMs and is relevant for various applications in non-polar liquids.

Electrodynamics of Electronic Paper Based on Total Internal Reflection

“…If an electric field is present at the solid-liquid interfaces, different kinds of interaction between the charges and the solid surface can occur. Two boundary conditions often observed in inverse micelle studies are considered here: adsorption/release and a blocking boundary [12,22]. It can be mentioned here that both boundary conditions lead to similar results.…”

“…Release of negative countercharges at the left solidliquid interface occurs as long as there is charge available on the surface (N l− > 0). The released charge is determined such that the field is zero at the interface [12,23]:…”

“…Two kinds of boundary conditions for the negative inverse micelles are compared by numerical simulation: the boundary condition of adsorption and release [12] (where the inverse micelles stick to the surface when they touch it and are released when the field is zero) and the blocking boundary condition [30] (where the inverse micelles form a diffuse double layer or Debye layer with thickness λ DL = (εε 0 k B T/2q 2 n − ) ≈ 100 nm near the interface when the electric field is directed from the liquid to the solid). There is a subtle but important difference in the location of the negative charges in steady state between the two kinds of boundary conditions.…”

“…As a side effect of these surfactants, other charged species, such as charged inverse micelles, are introduced which affect the switching dynamics [8,9]. On the topic of charged inverse micelles, many studies have focused on properties such as concentration and electrophoretic mobility [10], generation and recombination [11], interactions with interfaces [12], the influence of dielectric coatings [13], and steady-state and dynamic switching regimes [14]. On the topic of charged colloidal particles in nonpolar liquids, there are many investigations of the charging mechanisms mediated by charged or uncharged inverse micelles [15][16][17] and switching of particles [18,19].…”

Polarity-Dependent Adsorption of Inverse Micelles

“…In the last few decades, the field of nonpolar liquids containing inverse micelles has been thoroughly investigated. To measure the properties of charged inverse micelles, there are two commonly used methods: transient current measurements − and impedance spectroscopy. , These methods allow the measurement of bulk properties such as the concentration of charged inverse micelles and the electrophoretic mobility (and related to this the hydrodynamic radius) and details on the charge generation mechanism ,, and on interface phenomena. ,− When a potential difference is applied across a mixture, the behavior of charged inverse micelles near the electrodes depends on the type of surfactant system and on the type of surface. ,− Bulk dynamics based on drift and diffusion predict the formation of a diffuse double layer, though, due to adsorption of inverse micelles onto the electrode, this can evolve into a Stern layer. − Based on the measured capacitance of the Stern layer, the monovalent “core” of an adsorbed micelle appears to be situated even closer to the indium tin oxide (ITO) than the steric hindrance of the inverse micelle would allow, suggesting a different arrangement of the surfactant such as a hemi-micelle-like geometrical configuration. For example, in the case of AOT/dodecane, adsorption of charged inverse micelles on ITO is fast and bulk field screening is directly governed by Stern capacitances.…”