Alain Graciaa

The partitioning of complex surfactant mixtures between oil/water/microemulsion phases at high surfactant concentrations

Abstract A model describing the partitioning of surfactant molecules between excess and microemulsion phases which are in equilibrium is proposed. The important parameters characterizing the individual molecules comprising the mixture are the critical micelle concentrations in water and the partition coefficients between oil and water phases. The model considers the existence of a separate surfactant phase which is the palisade layer of a micelle and leads to predictions for both fractionation and phase concentrations of surfactant. Predictions based on this model have been compared to experimentally determined quantities and the agreement is good for all cases tested. The model leads to a relatively simple mathematical formulation which can be used to study the effect of varying the overall system surfactant concentration and of changing the system water-to-oil ratio.

Criteria for structuring surfactants to maximize solubilization of oil and water: II. Alkyl benzene sodium sulfonates

Abstract The general phase behavior of selected alkyl benzene sodium sulfonates was studied with the aim of determining specific factors which will enhance solubilization of oil and/or water in microemulsions. In pursuing this, it was discovered that decreasing the branching of the surfactant tail shifts the system to lower optimum ACN, narrows the width of the three-phase region, increases the solubilization parameter, and decreases the interfacial tension for systems in the optimum state, all other system variables remaining constant. Specifically, it was found that the width of the three-phase region was in simple inverse proportion to the solubilization parameter, and a previously proposed mathematical relationship between interfacial tension and solubilization was verified. Additionally, it was found that the alkyl chain tail length and the position of the benzene ring attachment exhibit linear mixing rules for optimum systems when the surfactants are mixed on a mole fraction basis.

Emulsion stability and phase behavior for ethoxylated nonyl phenol surfactants

Abstract The phase behavior of H 2 O/alkane/ethoxylated nonyl phenols was mapped for systems with added electrolyte and alcohols. The phase boundaries are mathematically described in terms of the variables, HLB, alkane carbon number, concentration of electrolyte and alcohol, and temperature. The maxima in emulsion stability (o/w and w/o) are found at the phase boundaries.

Partitioning of Nonionic and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases

Mixtures of different surfactant types have been proposed for application in polymer/micellar flooding processes. In some cases, severe fractionation of such mixtures is found even in short core experiments. In this paper, a new theory of surfactant partitioning between phases is developed and tested. Polydisperse nonionic surfactants blended with an anionic surfactant are considered. Important parameters in the theory are the critical micelle concentrations (CMCs) of surfactant mixtures in water and the partition coefficients of the surfactant between oil and water measured at total surfactant concentrations less than the CMC. From these simple experiments, surfactant fractionation in microemulsion systems can be modeled. The authors show that the fractionation of polydisperse ethoxylated nonionic surfactants between excess oil and water phases is not as severe in the presence of anionic surfactants as it is in systems containing only nonionic surfactants.

HLB, CMC, and phase behavior as related to hydrophobe branching

Abstract Increased hydrophobe branching is employed to increase water solubility of surfactants. This is often considered synonymous with increasing surfactant HLB. When HLB is viewed in the context of the phase behavior of oil/water/surfactant systems, it is seen that increased branching favors partitioning into the oil phase, thus lowering surfactant HLB despite an experimentally observed increase in CMC. An alternative to HLB is proposed which defines a surfactants properties based on the optimal alkane needed for the appropriate surfactant phase behavior.

The relationship between surfactant phase behavior and the creaming and coalescence of macroemulsions

Macroemulsions are inherently thermodynamically unstable systems which exhibit lifetimes which depend on the initial state of the system and the rates of creaming and coalescence. A previous study has shown an apparent relationship of emulsion stability to the thermodynamic equilibrium) phase behavior of systems containing surfactant/hydrocarbon/water M. Bourrel, A. Graciaa, R. S. Schechter, and W. H. Wade, J. Colloid Interface Sci.72, 161 (1979)) . It was found that macroemulsions are most stable at the boundaries which separate two phase systems from those which form three phases consisting of a microemulsion in equilibrium with excess hydrocarbon and water phases. The present investigation shows that on approaching the three-phase boundaries those factors, such as the density difference between phases, the continuous phase bulk viscosity, and the surface viscosity, which tend to influence the rate of creaming, all act to decrease it. Hence at the phase boundary creaming is shown to be a slow step, thereby causing the emulsion to appear to be stable. It was also found that, despite the fact that the surface viscosity is maximum at the boundaries, coalescence becomes more rapid as the boundaries are approached. Thus, while the time scale for creaming increases, that for coalescence decreases. Overall, then, macroemulsions formed well away from the phase boundaries cream first, but persist longest. Within the three-phase region where the surfactant system is balanced equal concentrations of surfactant in the excess phases) coalescence proceeds at a remarkable, but unexplained, speed. In this region macroemulsions coalesce before they cream and emulsion stability is least. These observations are shown to apply to systems in the presence of varying quantities of alcohol. The phase behavior was adjusted by varying the electrolyte concentrations.

Criteria for structuring surfactants to maximize solubilization of oil and water: part 1--commercial nonionics

It has been found for the four suites of nonionic surfactants studied that all those having the same HLB give the same optimal salinity, independent of their molecular weight. Increasing the surfactant hydrophobe molecular weight, compensated by an increase in the ethylene oxide number to retain the same HLB, improves surfactant performance. Increasing the surfactant hydrophobe chain length, with the requisite increase in ethylene oxide content to keep the same HLB, improves surfactant performance. For a variety of hydrophobes and ethylene oxide contents but remaining at the optimal line, (a) the width of the three-phase regime has a simple inverse relation to solubilization, (b) IFT is related directly to ACN and is related inversely to molecular weight, (c) solubilization is diminished by increasing ACN and diminished surfactant molecular weight, and (d) the product of IFT and solubilization squared is constant for a variety of system configurations. There is some evidence, based on the ethoxylated octadecyl phenol studied, that nonionics with properties better than those of currently commercially available species can be built.

Differentiation of continuous and discontinuous phases of water-in-oil microemulsions using dialysis

Abstract The application of dialysis to establish the chemical composition of the continuous phase of an oil-in-water microemulsion is described. Applied to saturated microemulsions, the method is shown to yield results in full agreement with the titration technique. It is also shown to be applicable to untitratable systems such as unsaturated microemulsions or complex five-component microemulsions which have not been studied by any other method.