Two model surfactant systems, one based on Texas 1 and the other on sodium dodecyl sulfate, were developed to give ultralow interfacial tensions and middle phase microemulsions when equilibrated with oil. Examination of their aqueous and microemulsion phase behavior, and comparison of the results with results of similar studies made on a system based on WITCO TRS 10-410, led to the conclusion that it is possible to generalize the phase behavior. The liquid crystalline spherulitic and lamellar textures observed in all these systems are the only homogeneous, non-phase separating fluids which can produce ultralow tensions on contact with oil. Mapping of the phase behavior of the two model surfactant systems showed that existence of the middle phase is relatively insensitive to surfactant concentration but quite dependent on cosurfactant concentration. Preliminary study of polymer-surfactant interactions confirmed the previously reported phase separation effect. A new temperature controlled polarized light screening device was built and has already been put to use for discrimination of isotropy, birefringence, scattering and interfacial phenomena insystems of interest for enhanced oil recovery.

The effects of temperature and of divalent ion concentration on the structure of aqueous surfactant solutions have been determined. As temperature increases, the salinity range where liquid crystalline phases exist is narrowed. At sufficiently high temperatures the liquid crystal "melts" and only isotropic phases are observed. These are an aqueous phase and, when partial immiscibility of alcohol and brine occurs, an alcohol rich phase as well. The effect of divalent ions on aqueous solution structure is basically the same as that of monovalent ions, but smaller quantities of divalent ions are needed to bring about the same phase changes. In the particular system studied addition of one mole of Ca+ was equivalent to addition of about 11.5 moles of Na+. We have extended our model of drop size in microemulsions to include the effect of drop dispersion. A hard sphere model was used to describe dispersion effects. With dispersion, drop size is slightly smaller for both oil-continuous and water-continuous microemulsions than predicted by the previous analysis which considered film properties alone.

The effects of temperature and of divalent ion concentration on the structure of aqueous surfactant solutions have been determined. As temperature increases, the salinity range where liquid crystalline phases exist is narrowed. At sufficiently high temperatures the liquid crystal "melts" and only isotropic phases are observed. These are an aqueous phase and, when partial immiscibility of alcohol and brine occurs, an alcohol rich phase as well. The effect of divalent ions on aqueous solution structure is basically the same as that of monovalent ions, but smaller quantities of divalent ions are needed to bring about the same phase changes. In the particular system studied addition of one mole of Ca+ was equivalent to addition of about 11.5 moles of Na+. We have extended our model of drop size in microemulsions to include the effect of drop dispersion. A hard sphere model was used to describe dispersion effects. With dispersion, drop size is slightly smaller for both oil-continuous and water-continuous microemulsions than predicted by the previous analysis which considered film properties alone.

The polarizing microscope was used to study the structure of aqueous solutions of petroleum sulfonates in the composition range planned for injection. All the surfactants studied showed a basic pattern of transformation between one structure and another over a relatively narrow range of salinities. As the salinity where this transformation occurs increases, so does the optimum salinity with a given oil, the condition of lowest interfacial tension. A polarized light box is being: developed to permit rapid determination of solution structure without the microscope since information on structure may be useful in the early stages -0f surfactant selection. Solutions containing a well-characterized surfactant, sodium dodecyl sulfate, were found to have the same basic structure pattern as the sulfonates. Hence, further experiments with this simple material should provide information relevant to the more complex petroleum sulfonates. The microscope was used to observe the dynamic contacting process between a surfactant solution and oil. Equilibration proceeds more rapidly at high salinities, mainly because of the spontaneous emulsification which occurs under these conditions. The ultracentrifuge was used to study microemulsions containing a conventional petroleum sulfonate. Results were similar to previous results for synthetic sulfonates except in a region where interfacial tension and solubilization results for the conventional sulfonate were anomalous. Progress was made in development of a theory to predict drop size in microemulsions, an important property influencing both phase behavior and interfacial tension.