Salting-Out Effect Induced by Temperature Cycling on a Water/Nonionic Surfactant/Oil System

Abstract

This paper presents original effects induced by temperature cycling on the transitional phase inversion of emulsions, stabilized by a nonionic polyethoxylated C18E6 surfactant model. The phase inversion follow-up is performed by electrical conductivity measurements, which involves focusing the study on the shape and location of the emulsion inversion region. In that way, new observations are brought out as a gradual evolution of the emulsion inversion along the cycling process. Two alternative approaches are considered for tackling these results: (i) first, a molecular approach regarding the particular organization and rearrangement of water clusters surrounding the surfactant polymer polar head, and (ii) second, a thermodynamic approach only considering the whole Gibbs free energy of the system. The volumic approaches are transposed, here, to the water/oil interface, and disclose that the phase inversion zone is included in a metastable region, able to stabilize for a given temperature, either metastable O/W emulsions or stable W/O ones. In that way, this study proposes novel and complementary insights into the phenomena governing the emulsion phase inversion.

Effect of Salts on Formation and Stability of Vitamin E-Enriched Mini-emulsions Produced by Spontaneous Emulsification

“…Previously, this affect has been attributed to the fact that these ions promote structure formation of bulk water around the ions, thereby reducing the amount of water molecules available to hydrate the surfactant headgroups. 18 In an alternative interpretation of the Hofmeister series, Kabalnov et al 44 suggested that the salting-in and salting-out phenomena have an interfacial origin driven by preferential adsorption/desorption of salt ions at the hydrophilic headgroup of the nonionic surfactant monolayers. Adding NaCl as a nonadsorbing salt dehydrates the hydrophilic headgroups through an osmotic effect associated with preferential ion exclusion, 44 thereby altering the optimum curvature and decreasing the PIT.…”

Liquid crystals and emulsions in the formulation of drug carriers

“…Later on, with a further temperature increase, the water phase disjoins into separate droplets, whereas continuity is maintained within the oily phase. The reverse transformations are observed when temperature is progressively decreased, and several thermal cycles can be repeated, but conductivity curves maintain their shape, though they are slightly shifted toward lower temperatures [12].…”

1,3-Butanediol as a co-solvent for the surfactant solutions

“…At high temperature values, water molecules behave as a poor solvent [12]. In addition to the disruption in the structure of water molecules caused by temperature, adding 1,3-butanediol will increase the extent of that disruption.…”