Conductivity of water-in-oil microemulsions stabilized by mixed surfactants (original) (raw)
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Conductivity of reverse microemulsion
The electrical conductivity of D 2 O-in-n-heptane microemulsions stabilized by cationic/nonionic surfactant mixtures was studied as a function of D 2 O content, surfactant concentration, and surfactant mixture composition. The surfactants employed were cationic di-ndidodecyldimethylammonium bromide, DDAB, nonionic poly(oxyethylene) monododecyl ethers, C 12 E J , with J = 3-8 and 23, nonionic polymeric surfactants of the type PEO-PPO-PEO (Pluronic), and the reverse structure analogues (Pluronic R). Qualitative structural information was drawn from a comparison between the measured conductivity and that predicted by the charge fluctuation model for spherical droplets. The conductivity versus water content curves were found to be typical for water-in-oil systems composed of spherical droplets. From the effect of blending nonionic surfactant with DDAB on the measured conductivities, it was concluded that microemulsion conductivity is independent of the concentration of cationic surfactant (DDAB). This finding agrees well with theoretical microemulsion conductivity models. 2004 Elsevier Inc. All rights reserved.
The Journal of Physical Chemistry, 1990
Ternary water-in-oil microemulsions using alkylbenzyldimethylammonium chloride (alkyl = dodecyl (N12), tetradecyl (N14), and hexadecyl (N16)) surfactants and benzene or chlorobenzene as oils have been investigated by means of electrical conductivity and NMR self-diffusion. The variations of the water self-diffusion coefficient with the [water]/[surfactant] molar concentration ratio w and with the volume fraction of benzene in the oil mixture in water/(benzene + chlorobenzene)/N16 microemulsions are well correlated with the changes of electrical conductivity, as expected from a model of microemulsions where the water cores of the droplets become increasingly connected above the percolation threshold. These connections, however, have a strongly dynamic character. This model permits us to explain the widely differing magnitudes of the changes of electrical conductivity, water self-diffusion coefficient, and rate of exchange of reactants between droplets upon increasing w. The self-diffusion coefficient of the oil has been found to be about half that of the bulk oil, as in studies reported by others.
The Journal of Physical Chemistry, 1990
Ternary water-in-oil microemulsions using alkylbenzyldimethylammonium chloride (alkyl = dodecyl (N12), tetradecyl (N14), and hexadecyl (N16)) surfactants and benzene or chlorobenzene as oils have been investigated by means of electrical conductivity and NMR self-diffusion. The variations of the water self-diffusion coefficient with the [water]/[surfactant] molar concentration ratio w and with the volume fraction of benzene in the oil mixture in water/(benzene + chlorobenzene)/N16 microemulsions are well correlated with the changes of electrical conductivity, as expected from a model of microemulsions where the water cores of the droplets become increasingly connected above the percolation threshold. These connections, however, have a strongly dynamic character. This model permits us to explain the widely differing magnitudes of the changes of electrical conductivity, water self-diffusion coefficient, and rate of exchange of reactants between droplets upon increasing w. The self-diffusion coefficient of the oil has been found to be about half that of the bulk oil, as in studies reported by others.
Journal of Chemical & Engineering Data, 2011
One of the most important tools in enhanced oil recovery (EOR) is microemulsion flooding to recover residual oil trapped in the reservoir after water flooding. The solubilization and phase equilibria of oilÀwater microemulsion have been studied with special attention on the role of alkane carbon number (ACN) of hydrocarbon, surfactant, and cosurfactant concentration on the formation of microemulsion. The ability of anionic and cationic microemulsion systems to solubilize alcohol has been investigated for different hydrocarbons. The effect of additives (NaCl salt with different concentrations) on electrical conductivity was studied by dropwise addition of brine in different concentrations to justify percolation of the microemulsion systems. The temperature effect on conductivity of microemulsions was also studied. Different aliphatic hydrocarbons (C 6 to C 12) and aromatic hydrocarbons such as benzene and toluene were used as synthetic oils. For the preparation of microemulsions, propan-2-ol and 3-methyl-1-butanol were selected as cosurfactants. The dependence of concentrations of the cosurfactant and surfactant on the boundary phase separation was also investigated.
Fluid Phase Equilibria, 2014
The present study is focused on the determination of the solubilization capacity and conductance behavior of mixed microemulsions [AOT/Brij-56 or Brij-58 or Brij-76 or TX-100 or Tween-80/Hp or Dc or IPM/water] in presence of ionic liquids (ILs) of different chemical structures and physicochemical properties [viz. bmimCl, hmimCl, bmimBF 4 and BzmimCl] at different compositions (X nonionic = 0, 0.1) at fixed surfactant concentration and temperature. Synergism in solubilization capacity has been evidenced in presence of ILs. All these systems exhibit volumeinduced percolation of conductance. The maximum solubilization capacity (ω 0,max), [IL] max (concentration of ILs at which synergism occurs) and volume-induced percolation threshold (ω p) have been found to influence by alkyl side-chain length, anion and polarity of ILs, and polar head group, hydrophobic moiety and content of nonionic surfactant and type of oils. Different solubilization sites of bmimCl and hmimCl have been proposed. ILs have been found to be more efficient additives than NaCl in respect of enhancing ω 0,max with less [IL] max and reducing ω p. The microstructure of AOT and AOT/Brij-56 systems at different X nonionic (= 0, 0.1) has been determined by DLS and FTIR measurements in absence and presence of ILs. Droplet diameter (d h) decreases and relative population of bound water increases with increase in [IL]. An attempt has been made to correlate the solubilization capacity in presence of ILs with percolation of conductance vis-à-vis droplet dimensions and the states of confined water to underline mechanism of solubilization phenomenon in these systems.
Connectivity-controlled charge transport in water-in-oil microemulsions
Chemical Physics Letters, 1986
Current-voltage characteristics of water/AOT/isooctane (W/O) mtcroemulsions were studied. The measured current consists of two components: an instantaneously responding part which indicates the degree of connectivtty of the dtspersed aqueous nanodroplets at any gtven temperature and concentratton. and a slowly rtsmg part which is due to structural changes of the microemulston Induced by the electric fteld.
Journal of Surfactants and Detergents, 2010
Interfacial behavior, structural and thermodynamic parameters of a water/(surfactant+n-butanol)/n-heptane water-in-oil (w/o) microemulsion have been investigated using the dilution technique at different temperatures, and [water]/[surfactant] mole ratios. The cationic surfactants used were alkyltrimethyl ammonium bromides (CnTAB, n = 10, 14 and 16) while the nonionic surfactants were polyoxyethylene (20) sorbitan monoalkanoates (polysorbate), viz., palmitate (PS 40), stearate (PS 60) and oleate (PS 80). The distribution of cosurfactant between the oil–water interface and the bulk oil at the threshold level of stability, and the thermodynamics of transfer of the cosurfactant from the bulk oil to the interface were evaluated. Structural parameters such as the dimensions, population density and effective water pool radius of the dispersed water droplets in the oil phase and the interfacial population of the surfactant and cosurfactant have been evaluated in terms of the surfactant chain length.
Effect of the Solvent on the Water Properties of Water/Oil Microemulsions
Journal of Colloid and Interface Science, 1999
Using IR spectroscopy and the UV-Vis absorption spectra of solubilized methyl orange (MO) as a probe, the properties of the water pool of some bis(2-ethylhexyl) sodium sulfosuccinate, (Aerosol OT) w/o microemulsions were investigated. The solvents used to prepare the micromulsions were cyclohexane, isooctane, and toluene. From IR water spectra, four different water species were detected. The relative amounts are found to depend on the waterto-surfactant molar ratio and also on the solvent. The water pool dielectric constants were determined from the position of the maximum of the MO absorption spectrum. The polarity increases as the water content solubilized in the microemulsions increases and also depends on the solvent.
Conductivity study of the microemulsion system sodium dodecyl sulfate-hexylamine-heptane-water
Journal of Colloid and Interface Science, 1987
Conductivity measurements on this system are interpreted in terms of the percolation and effective medium theories. From this interpretation, the ratio of hexylamine to sodium dodeeyl sulfate in the microemulsion droplet surfaces can be deduced. Following that determination it is possible to obtain approximate values for the radius of the water pools and the number and surface area of droplets per unit volume of the microemulsion system.
Transport properties of alternative fuel microemulsions based on sugar surfactant
Journal of Dispersion Science and Technology, 2016
Electrical conductivity of fuel microemulsion composed of diesel, pentanol, water and sucrose laurate as surfactant was investigated over a wide range of water content varying from 0 to 90 wt.% and temperature varying from 10 to 50ºC. Conductivity measurements were performed on samples, the composition of which lie along the one phase channel using conductivity meter. Activation energy of conduction flow was evaluated. The hydrodynamic radius as a function of temperature in the aqueous phase rich region (90 wt.%) was measured using dynamic light scattering method (DLS). The microstructure of microemulsion was further investigated by NMR diffusometry by which the selfdiffusion coefficients for water were determined at 25 o C. Electrical conductivity increases with water content up to 40 wt.% and percolation threshold was observed, and then stabilizes between 40 and 80 wt.% then decreases. Percolation threshold temperature at constant composition was monitored as 36ºC for water contents below 80 wt.% and 34ºC for water contents above. As predicted by the conductivity measurements, the determined self-diffusion coefficients of water confirmed the structural transition from discrete water in oil droplets to bicontinuous phase and finally to oil in water droplet microemulsion.