Investigation of Various Types of Inverse Micelles in Nonpolar Liquids Using Transient Current Measurements

Karvar, Masoumeh; Strubbe, Filip; Beunis, Filip; Kemp, Roger; Smith, Nathan J.; Goulding, Mark; Neyts, Kristiaan

doi:10.1021/la502287m

Cited by 21 publications

(53 citation statements)

References 34 publications

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“…In our previous study we found a mobility of 3.6 × 10 −9 m 2 V −1 s −1 , and a concentration of 6.0 × 10 18 m −3 per weight percent for charged AOT inverse micelles. 40 The steady state currents for devices with Al 2 O 3 coated electrodes with thicknesses of 10, 27, and 57 μm are shown in Figures 3(a−c) For example, in Figure 3a the measurement in a 10 μm device at the lowest concentration of ϕ m = 0.0003 shows a linearly increasing current up to the saturation voltage of 1 V. Above this saturation voltage the current is not exactly constant but is slowly increasing less than proportionally with the voltage. Because of this it makes sense to define the saturation voltage as the voltage at which a significant deviation from the linear increase is observed.…”

Section: Experimental Datamentioning

confidence: 99%

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Charging Dynamics of Aerosol OT Inverse Micelles

et al. 2015

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Aerosol OT (AOT) is a commonly used surfactant and charging agent in nonpolar liquids. Properties such as the conductivity of AOT suspensions in nonpolar liquids and the behavior of charged AOT inverse micelles at interfaces have been studied recently, but still little is known about the generation dynamics of charged AOT inverse micelles. In this article, the generation dynamics of charged AOT inverse micelles in dodecane are investigated with transient current measurements. At low applied voltages, the generation rate is sufficiently fast to maintain the equilibrium concentration of charged inverse micelles, such that the current scales proportionally with the applied voltage. However, above a threshold voltage the current becomes limited by the generation of charged inverse micelles. Al 2 O 3-coated electrodes are used to achieve these high-voltage current measurements while reducing surface generation currents. The dependency of the resulting generation-limited currents with the micelle concentration and the liquid volume is compatible with a bulk disproportionation mechanism. The measured currents are analyzed using a model based on drift, generation, and recombination of charged inverse micelles and the corresponding generation and recombination rates of charged AOT inverse micelles have been determined. INTRODUCTIONSurfactants are widely used for charging colloidal particles in reflective displays, 1−8 inkjet printing, 9 electrorheological fluids, 10 emulsion polymerization, 11,12 and dry cleaning. 13Over recent years, Anionic sodium bis (2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT) with its double-tail and polar headgroup has attracted increasing attention in aqueous, 14,15 nonaqueous 16−19 and water-in-oil (w/o) microemulsions. 20−26 During the last decades, different methods have been used to investigate the properties of AOT inverse micelles in nonpolar solvents. Peri has combined ultracentrifugation, light scattering, and viscometric measurements of AOT in various solvents, and he has suggested that AOT inverse micelles are monodisperse and spherical.27 Ekwall et al. have found similar results by using light and X-ray scattering. 28 Their studies indicate that the aggregation number N g , the number of monomers per inverse micelle, for AOT is about 20−30. Using a photon correlation experiment, Zulauf and Eicke 29,30,29,30 have studied the aggregation number of AOT micelles over a wide range of concentrations and in different solvents.27,28 Kotlarchyk et al. have used small-angle neutron scattering (SANS) and found an aggregation number of 22 ± 2 monomers per micelle. This difference can be explained by the hygroscopic properties of AOT, which makes the micelles absorb ambient moisture, and increases the conductivity of the AOT solution. 34 The charge-bearing entities are either trace ions such as formed from the dissociation of water into H + and OH − , or even charged AOT molecules that have released a H + . When two micelles collide there is a chance that these charged entities are e...

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Section: Experimental Datamentioning

confidence: 99%

“…For the surfactant OLOA1200 38 and in more detail for OLOA 11K 40 this is achieved by measuring generation-limited quasi steady-state currents. These generation-limited currents are due to bulk disproportionation since they scale with the square of the surfactant concentration and scale proportionally with the liquid volume.…”

Section: Introductionmentioning

confidence: 99%

Charging Dynamics of Aerosol OT Inverse Micelles

et al. 2015

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“…The surfactants OLOA 11K (r ≈ 5.5 nm 11,25,26 ) and Span 80 (r ≈ 4 nm 26 ) are non-ionic while Solsperse 13940 (r ≈ 8 nm 26 ) is an ionic surfactant. The second category includes surfactant systems such as ionic sodium dioctylsulfosuccinate or Aerosol OT (AOT) (r ≈ 1.6 nm 2,3,26 ) and non-ionic sorbitan trioleate or Span 85 (r ≈ 3 nm 26,27 ), in which the generation rate of CIMs is much higher than their transportation rate to the opposite polarity electrode on application of an electric field. Therefore, in these surfactant systems, the concentration of CIMs in the bulk always remains approximately equal to the equilibrium concentration 24,26 .…”

Section: Introductionmentioning

confidence: 99%

“…The second category includes surfactant systems such as ionic sodium dioctylsulfosuccinate or Aerosol OT (AOT) (r ≈ 1.6 nm 2,3,26 ) and non-ionic sorbitan trioleate or Span 85 (r ≈ 3 nm 26,27 ), in which the generation rate of CIMs is much higher than their transportation rate to the opposite polarity electrode on application of an electric field. Therefore, in these surfactant systems, the concentration of CIMs in the bulk always remains approximately equal to the equilibrium concentration 24,26 . Also, the behavior at interfaces of each category of CIMs is different, the CIMs of the first category surfactant systems end up in a diffuse double layer 28 while that of the second category CIMs form interface layers 24 at the electrodes.…”

Section: Introductionmentioning

confidence: 99%

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

Prasad

Strubbe

Beunis

et al. 2016

Phys. Chem. Chem. Phys.

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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.

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“…24,26,39 Measuring transient currents in response to a voltage step is a well-known sensitive technique for studying the surfactantmediated charging and charge dynamics in nonpolar systems. 25,39,40 In the case of surfactant systems such as OLOA 11K, Span 80, and Solsperse 13940, when the voltage is reversed abruptly (V 0 → −V 1 ) after a sufficiently long polarizing voltage step (0 → V 0, V 0 > 1 V, t 0 > 100 s), a second peak is observed in the transient current, which is not explained by drift and diffusion. 29 Measurements have shown that the integral of this peak increases with increasing duration of the polarizing voltage step, with increasing device thickness, and with increasing mass fraction of surfactant in the mixture.…”

Section: ■ Introductionmentioning

confidence: 99%

Different Types of Charged-Inverse Micelles in Nonpolar Media

et al. 2016

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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...

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Investigation of Various Types of Inverse Micelles in Nonpolar Liquids Using Transient Current Measurements

Cited by 21 publications

References 34 publications

Charging Dynamics of Aerosol OT Inverse Micelles

Charging Dynamics of Aerosol OT Inverse Micelles

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

Different Types of Charged-Inverse Micelles in Nonpolar Media

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