Robert S. Schechter

Adsorption of surfactants on mineral oxide surfaces from aqueous solutions: I: Isomerically pure anionic surfactants

Abstract Adsorption isotherms for three isomerically pure alkylbenzene sulfonates were measured on alumina and kaolinite from aqueous solutions. A patchwise adsorption model, which incorporates bilayer adsorption, lateral interactions, and two-dimensional phase transitions, is developed and shown to describe the observed isotherms below the CMC. As expected, Henrys Law describes the adsorption at sufficiently low surfactant concentrations. In this region, only unassociated, first-layer, surfactant molecules are present on the surface and at least the terminal 10th through the 12th carbons in the alkyl chain interact strongly with the surface, in addition to the charged head-surface electrostatic attraction. The adsorption increases rapidly beyond a certain concentration. At this concentration, hemimicelles resulting from lateral interaction between adsorbed surfactants first appear on the most energetic surface patches. At still higher concentrations, successively less energetic patches are sites for two-dimensional phase transitions forming hemimicelles. The environment for methylene groups in the hemimicelle is more favorable than that in a micelle. Above the CMC, adsorption is independent of concentration. This indicates that micelles do not adsorb significantly and that the pseudo-phase separation model is a good approximation for these systems.

Factors controlling the hydrodynamic detachment of particles from surfaces

Abstract The detachment of colloidal particles (5 to 40 μm) from surfaces has been studied. The influence of several variables such as flow rate, particle size, particle elasticity, ionic strength, pH, and gravity has been considered. Experiments were conducted to measure the critical hydrodynamic force required to detach particles from a flat glass substrate. It was demonstrated by conducting centrifuge experiments that the mechanism of detachment is rolling rather than sliding or lifting. The influence of particle size and elasticity as well as the surface chemical interactions between the particle and the substrate was included in a model that adequately explains the observed behavior. A consistent method is presented to compute the deformation of the particle and the adhesion and lift forces acting on it at equilibrium. These quantities allow us to compute the critical hydrodynamic force required for particle release. A comparison of the computed and experimentally measured forces shows good agreement, indicating that the essential physics of the problem has been captured in the model.

A correlation for phase behavior of nonionic surfactants

Abstract In previous studies, the systematics of variation of phase behavior of oil/water/surfactant systems have been detailed for anionic surfactants. The present study details the behavior of such systems with nonionic surfactants, including the variables: temperature, alcohol type and concentration, added electrolyte, ethylene oxide number of the surfactant, alkane molecular weight for the oil phase, and the hydrophobic molecular weight for the surfactant.

The application of low interfacial tension scaling rules to binary hydrocarbon mixtures

Abstract For a given electrolyte concentration, aqueous petroleum sulfonate surfactants in a contact with alkanes, alkylbenzenes, or alkylcyclohexanes as the second phase yield low interfacial tensions for only a single member of each homologous hydrocarbon series. For a particular equivalent weight surfactant and electrolyte concentration, the three hydrocarbons might typically be octane, octylbenzene, and butylcyclohexane. It is shown that appropriate mixtures of other hydrocarbon members of these series will produce low interfacial tensions if the average molecular weight is identical to octane and if phenyl and cyclohexyl groups are assumed to contribute zero and four carbons, respectively, to the attached alkyl side chains. Similar scaling rules are developed for groups in molecular species such as decalin and 1-methyl naphthalene.

The utilization of petroleum sulfonates for producing low interfacial tensions between hydrocarbons and water

Abstract Complex anionic surfactant mixtures selectively generate low interfacial tensions for aqueous phases in combination with select pure hydrocarbons. The hydrocarbon behavior is largely governed by the alkyl groups. There is some evidence of a direct relationship between hydrocarbon and surfactant molecular weight for attaining minimal tension. The classical CMC concept is not valid for the surfactants studied.

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.

Alkyl benzene sulfonates for producing low interfacial tensions between hydrocarbons and water

Abstract The effectiveness of various alkyl benzene sulfonates in reducing hydrocarbon-water interfacial tensions to very low values is examined. The length of the alkyl chain is varied and isomers, with the benzene ring attached to different positions on the alkyl chain, are studied. Those compounds with the ring close to one end of the chain are very insoluble in water and consequently the various surfactants are compared in solutions containing certain alcohols. Under these conditions, many yield tensions in the range of 10 −3 dyn cm −1 . Against the homologous series of alkanes, each surfactant formulation produced a minimum tension at a particular alkane carbon number. The manner in which the position of this minimum shifts as the surfactant structure is changed is examined in some detail.

Surfactants for producing low interfacial tensions I: Linear alkyl benzene sulfonates

Abstract and SummaryThe synthesis of a variety of linear alkylbenzene-sulfonates is described. These materials have been examined for their ability to promote every low interfacial tensions between alkanes, alkylbenzenes, or alkylcyclohexanes and water. Each surfactant gives its lowest tension against a particular member of each of these homologous series. For these surfactant struc-tures, the magnitude of its minimum tension is determined by the oil phase equivalent alkane carbon number (EACN) and structure and is largely independent of the particular surfactant used. The position of the minimum tension within the alkane series varies in a systematic and predictable manner. The significance of these results for tertiary oil recovery by surfactant flooding is discussed.

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.

The stability of foams: Dependence of observation on the bubble size distribution

The rate of foam collapse owing to interbubble gas diffusion is shown to be a sensitive function of the initial distribution of bubble sizes. Experimental evidence is presented to support these theoretical conclusions. The poor reproducibility of existing foam stability tests can be understood in terms of this sensitivity. The foam surface area decreases as a bilinear exponential function of time. One of the two characteristic time constants appears to be related to a gravity drainage mechanism while the second one is determined by the rates of gas diffusion between bubbles.