Phase behaviour and physicochemical properties of triton X 100 and aerosol OT induced micro emulsions of hydrocarbons and water in presence of n-butanol

Abstract

Phase diagrams of microemulsions composed of water/ oil/ AOT<em>/ n</em>-butanol and water/ oil/TX <em>&nbsp;</em>100/<em>n</em>-butanol are presented. The oils used are: n-hexane, n-heptane, n-octane and n-decane. Small lamellar zones appear with AOT along with large isotropic microemulsion areas. The 1:1 (wt/wt) ratio of surfactant- cosurfactant produces appreciable microemulsion area. At constant surfactant-cosurfactant ratio, the microemulsion areas decrease with the chain length of the alkanes. The minimum percentage of AOT required for dissolving about 40-50 wt % of water in hexane is - 8 wt %, which increases from 8-15 wt % for heptane, octane and decane. TX 100 imparts less microemulsion area than AOT with increase in alkane chain length. The conductances, viscosities, specific volumes and compressibilities of both the microemulsion systems at 1:1 (wt/wt) surfactant-cosurfactant ratio have been determined within no-water-to-no-oil limit. The-viseosity is maximum-at -31 vol % water. The conductance-sharplyin creases after addition of 0 01 % water. Both the specific volumes and the compressibilities decrease with increase in water content. The microemulsions become more compact with increase in water content; the ion conductance increases due to the combined effects of increased dielectric constant and channel formation. A comparison among the hydrocarbons on the basis of Walden product (&lambda;&eta;), the product of specific volume and the compressibility (v&beta;^-1), the excess specific volume (v_ex) and the excess compressibility (&beta;_ex) at different stages of water addition, shows that the viscosities and conductances of AOT based systems compensate each other at low and high percentages of water and not in the intermediate range. The v&beta;^-1 and v_ex values for both the AOT and TX 100 based systems suggest swelled microemulsions with increase in alkane chain length, particularly at lower percentages of water; these even out at higher water levels. The internal degree of flexibility is more for AOT based than that for TX 100 based microemulsions.