Dielectric relaxation and percolation phenomena in ternary microemulsions

Peyrelasse, J.; Moha-Ouchane, M.; Boned, Christian

doi:10.1103/physreva.38.904

Cited by 50 publications

(23 citation statements)

References 27 publications

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“…However, the values obtained for the critical exponent vary considerably. Whereas Bhattacharja et al [33] gave s % 0.65 for the AOT/water/decane system, and Peyrelasse et al [34] s % 1.65, a value of s % 1.1, that is, similar to the critical exponent from conductivity data, was reported by Feldman et al [13] for the same system. Since the high-frequency permittivity does not depend markedly on the temperature (e 1 % 3.2 is obtained for the spectra of this investigation) a relation similar to Equation (4) , respectively.…”

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confidence: 57%

Percolating Microemulsions of Nonionic Surfactants Probed by Dielectric Spectroscopy

2005

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[a] Microemulsions are thermodynamically stable, isotropic transparent fluids of two immiscible liquids and a surface-active agent. They have been thoroughly investigated over the last few decades not only with respect to possible industrial applications but also due to their great theoretical interest. [1,2] On the oil-rich side of the phase diagram reverse micelles are formed which, in a first approximation, can be described as spherical water droplets with typical diameters in the range of % 10-60 nm, separated from the continuous oil phase by a surfactant monolayer. [3] In recent years such water-in-oil (W/O) microemulsions with ionic surfactants [generally bis(2-ethylhexyl)-sulfosuccinate, AOT] aroused considerable interest as model systems for the investigation of percolation transitions [4][5][6][7][8][9][10] and associated charge transport. [11,12] Investigations of the conductivity, s, and the dielectric relaxation (via probing the total complex permittivity, ĥ (n) = e'(n)Ài[e''(n) + s/(2pne 0 )] of the sample as a function of frequency n; e 0 is the electric field constant) of ionic W/O microemulsions not only revealed a marked rise of s, when the percolation limit of the reverse micelles is approached, but also related maxima in the principle relaxation time t [associated with the peak frequency of the dielectric loss, e''(n)] and of the static permittivity, e = lim n!0 -e'(n).[5, 7, 9, 10, 13] These effects are generally assigned to the exchange of charges between the reverse micelles, which is strongly facilitated when the droplets start to aggregate to loose clusters that continue to grow until the percolation limit is reached. Charge carriers in these systems are the surfactant ion, such as AOT À , and the usually much smaller and more mobile counterion, for example, Na + . [14] Whereas conductivity measurements on ionic microemulsions are easily performed, the major problem of dielectric studies is the presence of other relaxation processes which prevent a proper determination of the amplitude, the relaxation time and the band shape of the dielectric dispersion associated with charge hopping. Especially the interfacial polarization, arising from fast tangential motions of adsorbed counterions in the oil-water interface, is large in amplitude and in a similar frequency range.[13] This is unfortunate because-at least in principle-dielectric relaxation studies should provide more and complementary information to measurements of s.The investigation of percolation phenomena in nonionic microemulsions is notoriously difficult due to the lack of appropriate probes. Conductivity studies are not possible and also attempts of dielectric studies failed to yield interpretable data.[15] However, it is possible to replace water by a dilute salt solution (e.g. 10 À3 mol L À1 KCl) which does not noticeably affect the phase behaviour but provides sufficient charge carriers for a detectable signal. Several theoretical as well as experimental studies have been carried out on the conductivity of such "doted" micr...

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confidence: 57%

Percolating Microemulsions of Nonionic Surfactants Probed by Dielectric Spectroscopy

2005

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“…The enhanced conductance has been considered to take place by the formation of infinite clusters/association of dispersed water droplets (stabilized by the amphiphiles) in the oil continuous medium. The easy flow of charges (ions) takes place by "hopping" [18][19][20][21] from droplet to droplet or are transferred by way of "fusion, mass transfer and mass exchange" [22][23][24][25]. As a consequence of the ion transfer, the conductance can be enhanced by 100 to 1000 folds.…”

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confidence: 99%

Percolation phenomenon in mixed reverse micelles: The effect of additives

Paul

Mitra

2006

Journal of Colloid and Interface Science

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“…145 Concerning the percolation theory, similar equations as postulated for the conductivity have been suggested. 135 For normal aqueous microemulsions without the addition of any additives (polymers, thickeners), the viscosity percolation phenomenon could not be detected. One condition to observe percolation is that the viscosity of the continuous phase is significantly different from the viscosity of the polar phase.…”

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confidence: 99%