The HLD‐NAC Model for Extended Surfactant Microemulsions

Abstract

It has been confirmed that the structure of the alkyl group of an extended surfactant plays an important role in defining its interfacial properties. Alkyl groups containing a higher degree of b-branching (C2-branching) produce microemulsions with a larger characteristic length (n, the extent of solubilization in middle phases). This effect is explained on the basis that b-branching increases the hydrophobicity of the surfactant and decreases the optimal salinity of the microemulsion. Higher salinities produce a dehydration of the surfactant groups that lead to shorter extent of the interactions with the oil and the water. Larger characteristic lengths are desirable if the objective of the formulation is obtaining greater solubilization of oil and water, and lower interfacial tensions. Large characteristic lengths are, in most cases, associated with high interfacial rigidities, which are undesirable if rapid coalescence is required. However, mixtures of branched and linear extended surfactants produce large characteristic lengths and lower interfacial rigidities. The HLD-NAC model is able to reflect the experimental trends in solubilization of oil and water. The differences between the predictions of the model for the solubilization of oil and water in Type I and II formulations, respectively, highlight the complexities in the conformation of extended surfactants, particularly their PO groups, at oil-water interfaces and the need for advanced scattering techniques to evaluate these conformations.

How to Attain an Ultralow Interfacial Tension and a Three‐Phase Behavior with a Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 2. Performance Improvement Trends from Winsor's Premise to Currently Proposed Inter‐ and Intra‐Molecular Mixtures

“…The performance was found to be somehow related to the size of the polypropylene oxide extension and to the oil structure and size with different matching depending of the oil structure [182]. These properties were corroborated more recently for different structures and oil phases [18,59,[184][185][186][187][188][189][190][191][192][193][194][195][196][197].…”

“…In practice this may be done by increasing the rigidity up to the critical value, and to try to displace the critical value beyond which a liquid crystal would result in the system. In other words some changes are likely to alter the characteristic length and the rigidity in different ways, and thus allows a best compromise to be attained [18, 19]. …”

“…The minimum tension at the optimum which is taken as the performance estimate, written here as c* to indicate it is an optimum formulation value. In this case, c* depends on four formulation variables, three of which are independent, with the fourth one value taken to satisfy the HLD = 0 equation (18). The typical tridimensional graph shown in Fig.…”

Extended Surfactants Including an Alkoxylated Central Part Intermediate Producing a Gradual Polarity Transition—A Review of the Properties Used in Applications Such as Enhanced Oil Recovery and Polar Oil Solubilization in Microemulsions

“…The main research was dedicated to the influence of the surfactant type in similar Winsor III systems on the solubilization parameter SP*, i.e., the equal amounts of oil and water solubilized in a microemulsion single phase per unit amount of surfactant, and expressed as g/g, mL/mL, or g/mL (Barakat et al, , ; Graciaa et al, ). Other performance measurements such as the net average curvature (NAC) (Acosta et al, , , ) were proposed slightly away from the three‐phase behavior case, and they were found to follow similar general rules.…”

The UNIFAC model and the partition of alkyl and alkylphenol ethoxylate surfactants in the excess phases of middle phase microemulsions

“…Salager et al have also determined that the partition of surfactants in the excess phases of a middle phase microemulsion also correlate well with the values of HLD [15]. The HLD equation associated with the net-averagecurvature (HLD-NAC) model is used in formulation engineering to predict microemulsion phase behavior, shape, viscosity and volumes of microemulsion phases [26][27][28]. Surfactant-oil-water (SOW) systems can form oil in water (Type I), water in oil (Type II) or systems continuous in water and oil (Type III or IV) microemulsions.…”