Studies on Structure and Dynamics of Microemulsions II: Viscosity Behaviour of Water-in-Oil Microemulsions

Results of a detailed viscometric investigation on water-in-oil microemulsions using hexane, heptane, octane, iso-octane, decane, cyclohexane, xylene, and toluene as oils and Aerosol Orange-T (AOT) as the amphiphile are presented. Attempts have been made to examine the overall geometry and oilation of the dispersed particles. It has been found that the particles are close to spheres and the solvation by the oil is insignificant. The performance of the viscosity equations of Vand, Moulik, and Thomas on all the systems have been tested. Striking validity of all the three equations has been observed at constant water/AOT mole ratio (ω). A combined unified viscosity equation can also correlate the results. With variable ω all the equations fail to correlate the experimental results. Correlation of the equation parameters with both the carbon number and the molar mass of the open chain hydrocarbon oils has been attempted. Effects of added salts viz. NaC and NaCl on the viscosity behaviour of iso-octane based microemulsion have been also studied.