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.
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