Review on Some Confusion Produced by the Bicontinuous Microemulsion Terminology and Its Domains Microcurvature: A Simple Spatiotemporal Model at Optimum Formulation of Surfactant-Oil-Water Systems.

Fundamental studies have improved understanding of molecular-level properties and behavior in surfactant-oil-water (SOW) systems at equilibrium and under nonequilibrium conditions. However, confusion persists regarding the terms "microemulsion" and "curvature" in these systems. Microemulsion refers to a single-phase system that does not contain distinct oil or water droplets but at least four different structures with globular domains of nanometer size and sometimes arbitrary shape.

Formulation Improvements in the Applications of Surfactant-Oil-Water Systems Using the HLD Approach with Extended Surfactant Structure.

Soap applications for cleaning and personal care have been used for more than 4000 years, dating back to the pharaonic period, and have widely proliferated with the appearance of synthetic surfactants a century ago. Synthetic surfactants used to make macro-micro-nano-emulsions and foams are used in laundry and detergency, cosmetics and pharmaceuticals, food conditioning, emulsified paints, explosives, enhanced oil recovery, wastewater treatment, etc. The introduction of a multivariable approach such as the normalized hydrophilic-lipophilic deviation (HLD ) and of specific structures, tailored with an intramolecular extension to increase solubilization (the so-called extended surfactants), makes it possible to improve the results and performance in surfactant-oil-water systems and their applications.

Use of the normalized hydrophilic-lipophilic-deviation (HLD) equation for determining the equivalent alkane carbon number (EACN) of oils and the preferred alkane carbon number (PACN) of nonionic surfactants by the fish-tail method (FTM).

The standard HLD (Hydrophilic-Lipophilic-Deviation) equation expressing quantitatively the deviation from the "optimum formulation" of Surfactant/Oil/Water systems is normalized and simplified into a relation including only the three more meaningful formulation variables, namely (i) the "Preferred Alkane Carbon Number" PACN which expresses the amphiphilicity of the surfactant, (ii) the "Equivalent Alkane Carbon Number" EACN which accurately reflects the hydrophobicity of the oil and (iii) the temperature which has a strong influence on ethoxylated surfactants and is thus selected as an effective, continuous and reversible scanning variable. The PACN and EACN values, as well as the "temperature-sensitivity-coefficient"τ of surfactants are determined by reviewing available data in the literature for 17 nonionic n-alkyl polyglycol ether (CE) surfactants and 125 well-defined oils. The key information used is the so-called "fish-tail-temperature" T* which is a unique data point in true ternary CE/Oil/Water fish diagrams.

Instability of Emulsions Made with Surfactant-Oil-Water Systems at Optimum Formulation with Ultralow Interfacial Tension.

We have studied emulsions made with two- and three-phase oil-water-surfactant systems in which one of the phases is a microemulsion, the other phases being water or/and oil excess phases. Such systems have been extensively studied in the 1970-1980s for applications in enhanced oil recovery. It was found at that time that the emulsions became very unstable in the three-phase systems, but so far few explanations have been proposed.

Interfacial rheology of low interfacial tension systems using a new oscillating spinning drop method.

When surfactants adsorb at liquid interfaces, they not only decrease the surface tension, they confer rheological properties to the interfaces. There are two types of rheological parameters associated to interfacial layers: compression and shear. The elastic response is described by a storage modulus and the dissipation by a loss modulus or equivalently a surface viscosity.