Different Types of Charged-Inverse Micelles in Nonpolar Media

Abstract

Over the last few years, the electrodynamics of charged inverse micelles (CIMs) in nonpolar liquids and the generation mechanism and properties of newly generated CIMs have been studied extensively for the model system of polyisobutylene succinimide in dodecane. However, the newly generated CIMs, which accumulate at the electrodes when a continuous voltage is applied, behave differently compared to the regular CIMs present in equilibrium in the absence of a field. In this work, we use transient current measurements to investigate the behavior of the newly generated CIMs when the field is reduced to zero or reversed. We demonstrate that the newly generated CIMs do not participate in the diffuse double layer near the electrode formed by the regular CIMs but form an interface layer at the electrode surface. A fraction of the newly generated negative CIMs can be released from this interface layer when the field there becomes zero. The findings of this study provide a better understanding of fundamental processes in nonpolar liquids and are relevant for applications such as electronic ink displays and liquid toner printing. 23−26 have been used to study the mechanism of surfactant-mediated charging and charge stabilization in nonpolar media. From these studies, it has been concluded that charges in nonpolar surfactant systems exist in the form of inverse micelles that are formed above a certain surfactant concentration known as the critical micelle concentration. ■ INTRODUCTION11−13,27,28 A small fraction (10 −5 aerosol OT 11,13 and 0.1 polyisobutylene succinimide 24,29 (PIBS)) of the inverse micelles is charged as a result of a disproportionation/ comproportionation mechanism, 11,12,14,15,24,28 in which two uncharged inverse micelles exchange a charge and become a positively and a negatively charged inverse micelle and vice versa. Charged inverse micelles (CIMs) play an important role in charging and charge stabilization in nonpolar media. 11−15,30−32 Electrophoretic displays are based on the displacement of charged pigment particles between two electrodes in response to an applied voltage. 5,7,25 In these systems, surfactant is often added to charge and stabilize the pigment particles. 16,33,34 However, only a small fraction of surfactant molecules is adsorbed at the particle surfaces and other interfaces. Because of the presence of free CIMs, the nonpolar medium becomes more conductive, affecting the electric field and the switching characteristics of charged pigment particles. 21 Controlling the trajectory of particles in conductive media is challenging because of electrohydrodynamic flow, 7,29 which causes particle clustering 7 and pattern formation 35−37 at the electrodes, resulting in image degradation, increased power consumption, and reduced lifetimes of electrophoretic devices. 7 Many effects of charged inverse micelles can be studied without the presence of colloidal particles. 29,33,38 The electrical behavior of these nonpolar systems with surfactant is governed by the drift, diffusion, an...

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

“…Afterwards, the space between the substrates is refilled with pure dodecane and the same suction process is repeated. This suction and filling process is repeated 10 times to ensure that the liquid in the volume is completely replaced with pure dodecane 29 . …”

“…However, the integral of the second peak increases with increasing duration of the polarizing voltage step and eventually reaches a saturation level for high voltages. From this observation, it has been concluded that the second peak is a result of new charges generated during the quasi steady state of the polarizing voltage step 29 .…”

“…Previously, we have reported on two studies about the properties of generated CIMs and the mechanism of their release 25,29 .…”

Multiphase Microfluidics: Fundamentals, Fabrication, and Functions

“…Additionally, active surfactants, which are responsive to external stimuli such as light, chemical agents, pH, magnetic or electric fields, redox process, etc., are well known for their capacity to deform, drive, destruct, and coalesce emulsions. Some common stimuli and their effects on droplets or emulsions are shown in Figure .…”

Controlling the interfacial and bulk concentrations of spontaneously charged colloids in non-polar media

“…As a result, the Coulombic force in nonpolar solvents extends over larger distances and promotes the aggregation of nano-scale charged particles or the formation of solid precipitates [2][3][4]. Nevertheless, colloids may be stabilized in a dispersion by the addition of surfactants and ligands, such as the macromolecular self-assembly of isolated inverse micelles, which are essentially a ternary water-in-oil system [5,6], and the references therein.…”