Viscoelastic properties of paracrystalline phases appearing in water‐surface agent‐oil diagrams

Abstract

Synopsis The ternary mixtures investigated were obtained from water, mineral oil and ether-linked non-ionic surfactants (polyoxyethylene derivatives of oleic alcohol). The examination of the rheological properties of these mixtures, particularly the viscoelastic properties of the various phases encountered in these diagrams, was expanded. The phases examined were: - anisotropic paracrystalline phases: hexagonal phase and lamellar phase; - the isotropic paracrystalline phase: type I viscous isotropic phase. The measurement instrument used for this work was a creep rheometer. The paracrystalline phases were subjected to very low shear stresses, and the strains induced were recorded as a function of time. The analysis of creep functions obtained enabled us to construct a viscoelastic model and obtain the value of its parameters for each particular case. This analysis of the viscoelastic properties provides an accurate identification of each of the paracrystalline phases: the lamellar and isotropic viscous phases show respectively a Newtonian fluid nature with a yield value (Bingham model), and a perfect elastic solid. The hexagonal phase on the other hand shows an intermediate type of behaviour which is characterized by a well-defined retarded elasticity. This study could also lead to a microscopic interpretation of their structure.