Conductivity of water-in-oil microemulsions: a quantitative charge fluctuation model

Eicke, Hans‐Friedrich; Borkovec, Michal; Das-Gupta, Bikram

doi:10.1021/j100338a062

Cited by 267 publications

(245 citation statements)

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“…Devices with thicknesses d = 10, 27, and 57 μm are made, and the thickness is verified measuring optical interference with a PerkinElmer 25 and they proposed a model in order to predict the electrical conductivity of AOT-water-apolar microemulsions. 26 In the present study, no measures were taken to eliminate traces of ambient humidity in our mixtures. From exposure of a mixture to the ambient the conductivity can eventually increase up to 50% when the inverse micelles become saturated with water corresponding to about w = [H 2 O]/[AOT] = 0.25, but without changing their physical behavior.…”

Section: Methodsmentioning

confidence: 95%

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: Methodsmentioning

confidence: 95%

Charging Dynamics of Aerosol OT Inverse Micelles

et al. 2015

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“…Their conductivity is due to the charge of the droplets. Eicke 22 published in 1989 a model to predict the conductivity of such microemulsions, based on statistical mechanics, more precisely on equipartition of energy. He thus assumed that the mean Born energy for a droplet is half the thermal energy,…”

Section: Part Iii: Microemulsions: Theory and Discussionmentioning

confidence: 99%

Application of classical thermodynamics to the conductivity in non-polar media

Gourdin-Bertin

Chassagne

2016

The Journal of Chemical Physics

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Articles you may be interested inElectrical conductivity in non-polar media is a subject which recently regained interest. If most of experiments and theoretical developments were done more than 50 years ago, new experiments and theories have been recently published. As the electrical conductivity describes, at low field, the equilibrium state of a system, it is natural to apply theories based on equilibrium thermodynamics. In this article, well-established classical thermodynamics and solvations models are applied to recently published data. This enables to get a new insight in intriguing phenomena, such as the linear dependence of the conductivity on the concentration of ionic surfactant and the evaluation of conductivity for the mixture of two miscible fluids, such as alcohol and alcane, which have very different conductivities. Published by AIP Publishing. [http://dx

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“…Considering that water droplets are surrounded by a film of nonpolar tails of dodecyl sulfate anions and amyl or isoamyl chains, 14 its diffusion through the continuous oil medium must be slower than the one for Fc molecules. On the other hand, the net positive charge in the water droplets 36 is probably the reason for the decrease in the limiting current observed for water oxidation in the presence of Fc (see Figure 5). The ferricinium ion, Fc + , present near the electrode hinders the migration of positive charged droplets and consequently the water oxidation reaction rate decreases, this difficulty being expected to increase with Fc concentration.…”

Section: Electrochemical Measurementsmentioning

confidence: 96%

“…36 Consequently, its transport to the surface of the electrode is hindered by an unfavorable migration component. Moreover, water molecules must break the nonpolar barrier around the droplets and diffuse to the surface of the electrode before the charge transfer reaction takes place.…”

Section: Electrochemical Measurementsmentioning

confidence: 99%

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Water in soybean oil microemulsions as medium for electrochemical measurements

Mendonça¹,

Bica²,

Piatnicki³

2003

J. Braz. Chem. Soc.

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Microemulsões de água em óleo de soja (w/o ME) foram preparadas com dodecil sulfato de sódio (SDS) como surfactante e com os álcoois amílico ou isoamílico, como co-surfactantes. A composição 40,0% de óleo, 43,2% de álcool, 10,8% de SDS e 6,0% de água, em massa, na razão 1:4 [SDS]: [álcool], apresentou a maior estabilidade termodinâmica. O tamanho das gotículas e seu coeficiente de difusão nas microemulsões, D w/o , foram determinados por medidas de espalhamento de luz dinâmico (DLS). As reações de oxidação de ferroceno (Fc) e de água, e a redução de ácido oleico foram observadas nas ME por voltametria em um ultramicroeletrodo (ume) de disco de Pt. Os valores de D w/o determinados a partir de medidas eletroquímicas são menores do que os calculados a partir daquelas por DLS. Isto indica que a oxidação da água requer a difusão para o eletrodo tanto das gotículas como das moléculas de água nelas contidas. Os resultados evidenciam a possibilidade de determinação de analitos em óleos vegetais por métodos eletroanalíticos.Microemulsions of water in soybean oil (w/o ME) were prepared with sodium dodecyl sulfate (SDS) as surfactant and amyl or isoamyl alcohol, as co-surfactants. Microemulsions containing 40.0% oil, 43.2% alcohol, 10.8% SDS and 6.0% water in weight, in the ratio 1:4 [SDS]: [alcohol] showed the highest thermodynamic stability. The aqueous droplet size and its diffusion coefficient D w/o in the ME were determined through dynamic light scattering (DLS). Voltammetric measurements in the ME at a Pt disk ultramicroelectrode (ume) evidenced the oxidation of both water and ferrocene (Fc), and the reduction of oleic acid. The D w/o values calculated from the limiting current being lower than the ones obtained from DLS indicate that water oxidation probably requires diffusion towards the electrode of both the droplets and the water molecules from inside the droplets. The results show that electroanalytical determinations can be carried out in w/o ME. Keywords: microemulsions, soybean oil, voltammetry, ferrocene, oleic acid IntroductionEquilibria in water-oil interfaces have been studied in order to quantify solvent extraction as well as charge transfer processes. In this sense new analytical methodologies such as slow extrusion of water into a nonaqueous phase (and vice-versa) through a capillary, 1 the use of micrometric electrodes 2-3 and of microemulsions 4,5 (ME) have been proposed recently. Besides a significant decrease in costs and toxicity due to the decrease in organic solvents consumption, 6-8 water in oil ME allow to carry out electrochemical measurements due to the enhanced electrical conductivity imparted to the system by the presence of water.Microemulsions are thermodynamically stable systems composed of water, oil and surfactant, and, in some cases, an alcohol can be added as co-surfactant. 9-12 Their behavior is similar to the one of polar organic solvents and, although apparently homogeneous under visual observation, ME are actually microheterogeneous (perhaps nanoheterogeneous would be a better...

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Conductivity of water-in-oil microemulsions: a quantitative charge fluctuation model

Cited by 267 publications

References 0 publications

Charging Dynamics of Aerosol OT Inverse Micelles

Charging Dynamics of Aerosol OT Inverse Micelles

Application of classical thermodynamics to the conductivity in non-polar media

Water in soybean oil microemulsions as medium for electrochemical measurements

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