Viscosity, conductivity, and dielectric relaxation of waterless glycerol–sodium bis(2-ethylhexyl) sulfosuccinate–isooctane microemulsions: The percolation effect

The waterless microemulsion glycerol-AOT-isooctane [AOT, sodium bis(2-ethylhexyl) sulfosuccinate] was systematically studied as a function of temperature T, volume fraction (glycerol plus AOT) {φ}, molar ratio n=[glycerol]/[AOT], and the salt content pₛ in the glycerol. The properties studied are dynamic viscosity {η}, electric conductivity {σ}, and dielectric relaxation εR*. At fixed T, n, and pₛ an increase in the conductivity and dynamic viscosity is observed when the volume fraction increases. Dielectric relaxation may be represented as a generalized Davidson-Cole distribution of the relaxation time. The quantities (1/{σ})(d{σ}/d{φ}) and (1/{η})(d{η}/d{φ}) pass through a maximum, as does the static permittivity εₛ (in the latter case the maximum is often followed by a minimum). At the same time the inverse of the characteristic frequency of dielectric relaxation 1/νR passes through a maximum. The results are discussed in the framework of percolation theory. The application of the asymptotic laws of percolation is discussed. For viscosity, the analysis of the results provides a good comparison between theoretical and experimental values taking as critical percolation exponents {μ}'{}2 (for {φ}>φc), where φc is the percolation threshold and s'{}1.2 ({φ}φc), which are the values predicted by the dynamic theory of percolation. By determining the {η}({φ}) curves for various conditions, we were able to establish the variations of φc(T), φc(n), and φc(pₛ). It was observed that φc decreases when T and n increase or when pₛ decreases. This corresponds to an increase in the interactions between droplets within the system. Finally, according to the value of {φ}, the viscosity may increase or decrease with increasing temperature. This curious effect can be explained by appropriate application of percolation theory.