Inverse micelles as charge carriers in nonpolar liquids: Characterization with current measurements

Beunis, Filip; Strubbe, Filip; Karvar, Masoumeh; Drobchak, Oksana; Brans, Toon; Neyts, Kristiaan

doi:10.1016/j.cocis.2013.02.010

Cited by 32 publications

(68 citation statements)

References 57 publications

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“…29 The concentrations of positive and negative charged micelles are denoted as n + and n − (m −3 ). Assuming the valency of charged micelles z to be ±1 12,30 and from charge conservation, we can conclude that n + = n − at t = 0. In the model, we assume that positive and negative micelles have the same size and the same mobility μ = μ + = μ_ (m 2 ·V −1 ·s −1 ).…”

Section: Theorymentioning

confidence: 99%

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

Karvar¹,

Strubbe²,

Beunis³

et al. 2014

Langmuir

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Transient current measurements are used to characterize a wide variety of charge carriers in nonpolar liquids. The transient current method allows us to obtain both the concentration and mobility of charge carriers and therefore also the hydrodynamic radius using Stokes' law. In this article, five different surfactants in dodecane are investigated: OLOA11K, Solsperse13940, Span80, Span85, and AOT. We show that different types of currents are observed depending on the size of the inverse micelles. For large inverse micelles such as for OLOA11K, Solsperse13940, and Span80, the measurement of the transient current is straightforward because of the low steady-state current level. However, for small inverse micelles such as AOT and Span85, the current from the generation of charges is much larger such that high voltages, a small distance between the electrodes, and dielectric coatings on the electrodes are required to measure the signal related to the initially present charged inverse micelles. The estimated hydrodynamic radii of AOT and Span85, the two smallest inverse micelles, are in good agreement with the values reported in the literature. The comparison of the transient currents with simulations indicates that the dynamics of the charge transport are well-understood.

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Section: Theorymentioning

confidence: 99%

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

Karvar¹,

Strubbe²,

Beunis³

et al. 2014

Langmuir

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“…The current decreases rapidly at time scales t < 2d 2 /(μ(V 2 − V 1 )φ 1 ) which is roughly the time needed for the nonlinear part of the double layer to reach equilibrium. After that, the linear part of the double layer reaches the new equilibrium leading to an exponentially decreasing current with amplitude 8zen , V 1 = 3 V, and V 2 = 10 V. Using the value (α/β) 1/2 ≅ 51 estimated from the very similar surfactant OLOA1200 29,35 corresponding values for β and n ̅ 0 are obtained. Since β ≪ α the generation rate is in good approximation βn ̅ 0 2 ≅ αn ̅ 2 .…”

Section: Theorymentioning

confidence: 99%

“…As explained before, β and n ̅ 0 are obtained using the value (α/β) 1/2 ≅ 51 from an estimation of the concentration of uncharged inverse micelles in OLOA1200. 29,35 Considering the linear relationship between n ̅ and ϕ m (see Figure 3) the trendline I gen,lim = 3.05 × 10 −6 A × ϕ m 2 shows that I gen,lim is in fact proportional to n ̅ 2 , which is expected for a disproportionation model. The average value of the recombination constant is α = 3.4 × 10 −22 m 3 s −1 .…”

Section: Theorymentioning

confidence: 99%

“…The diffusion coefficient and mobility are related by D i = μ i kT/ze, with Boltzmann constant k and temperature T. Considering the small size of the micelles compared to the Bjerrum length in nonpolar liquids we expect a value z = z gen = 1 for both types of charged inverse micelles. 27,29 However, the size and therefore also the mobility and diffusion coefficient of the initially present and newly generated charged inverse micelles can potentially be different. The dynamics of the concentrations are determined by the following continuity equations and Gauss's law:…”

Section: Theorymentioning

confidence: 99%

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Characterizing Generated Charged Inverse Micelles with Transient Current Measurements

2015

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ABSTRACT:We investigate the generation of charged inverse micelles in nonpolar surfactant solutions relevant for applications such as electronic ink displays and liquid toners. When a voltage is applied across a thin layer of a nonpolar surfactant solution between planar electrodes, the generation of charged inverse micelles leads to a generation current. From current measurements it appears that such charged inverse micelles generated in the presence of an electric field behave differently compared to those present in equilibrium in the absence of a field. To examine the origin of this difference, transient current measurements in which the applied voltage is suddenly increased are used to measure the mobility and the amount of generated charged inverse micelles. The mobility and the corresponding hydrodynamic size are found to be similar to those of charged inverse micelles present in equilibrium, which indicates that other properties determine their different behavior. The amplitude and shape of the transient currents measured as a function of the surfactant concentration confirm that the charged inverse micelles are generated by bulk disproportionation. A theoretical model based on bulk disproportionation with simulations and analytical approximations is developed to analyze the experimental transient currents.

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“…41,42 E is the position-and time-dependent electrical field (V/m), D is the diffusion coefficient (m 2 /s) which is related to the mobility of charged inverse micelles μ by D = μk B T/ze. The electric field is determined by the externally applied potential difference V A and by space charge present in the bulk through Gauss's law ϵ r ϵ 0 (∂E/∂x) = ρ where ρ is the space charge density conserving overall charge neutrality ∫ −d/2 d/2 ρ dx = 0.…”

Section: Analytical Modelmentioning

confidence: 99%

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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Inverse micelles as charge carriers in nonpolar liquids: Characterization with current measurements

Cited by 32 publications

References 57 publications

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

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

Characterizing Generated Charged Inverse Micelles with Transient Current Measurements

Charging Dynamics of Aerosol OT Inverse Micelles

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