Dielectric study: II. Structural transitions in the liquid crystalline phase of water-in-oil microemulsions

• Published in: Journal of colloid and interface science Vol. 67; no. 3; pp. 457 - 464
• Main Authors: Senatra, Donatella, Giubilaro, Gabriella
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1978
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(78)90235-7

The complex permittivity, ϵ∗ = ϵ′ − jϵ″, of a water-in-dodecane microemulsion was studied in the frequency range 1.6 k Hz-50 MHz for water contents (mass fraction c) up to and beyond the inversion of the system into an oil-in-water type of dispersion. Within the concentration interval 0.31-0.41, labeled the nematic phase concentration region, c n , the behavior of ϵ′ and ϵ″, upon concentration, exhibited an abrupt increase followed by a decreasing trend for c > C n . The phenomenon was observable only in the low-frequency range; after the first megahertz decade, it was no longer detectable. The frequency-dependent behavior of ϵ′ in the c n region was comparable with that exhibited by the parallel component of the static dielectric constant ( ϵ ∥) of some oriented nematic liquid crystals with a positive dielectric anisotropy; the same analogy was found to apply to the frequency dependence of the microemulsion conductivity, σ(ν). Therefore, the peculiar dielectric behavior in the c n region was ascribed to a structural transition, from a waterin-oil dispersion to a nematic liquid crystalline phase, which develops as the water content of the system approaches a given “transition concentration” c t ≈ 0.31.