DIAMETER OF SODIUM DI-(2-ETHYLHEXYL)PHOSPHATE AND SODIUM DODECYLSULFATE REVERSE MICROEMULSION DROPLETS: EXPERIMENTAL DATA AND CALCULATION METHODS

Abstract

The article is concerned with study of diameters of reverse microemulsion droplets depending on the water content in sodium bis-(2-ethylhexyl)phosphate – decane – water and sodium dodecylsulfate – butanol-1 – decane – water systems. Hydrodinamic diameters of microemulsion droplets were determined by the method of dynamic light scattering. It increases from 5.9 to 9.7 nm with an increase in the molar ratio of water and sodium bis-(2-ethylhexyl)phosphate from 5.0 to 20.0 in the sodium bis-(2-ethylhexyl)phosphate – decane – water microemulsion. Diameter of microemulsion droplets in the sodium dodecylsulfate – butanol-1 – decane – water system increases from 2.4 to 8.6 nm with an increase in the molar ratio of water and dodecylsulfate from 7.5 to 30.0. It was shown that the dependence of the diameter (d) on the water content (W) is linear. The applicability of the experimental data on the area per surfactant molecule at the "water-oil" interface and literature data on the values of molar volumes of microemulsion components to calculate the diameter of microemulsion droplets was analyzed. It was shown that the equation of the form d = kW + b is suitable for describing the dependence of the diameter of microemulsion droplets on the water content in the sodium dodecyl sulfate-butanol – 1-decane-water system. Parameters k and b of this equation are calculated using the value of the area per surfactant molecule at the "water-oil" interface, which can be obtained from experimental data on interfacial tension. Values of the diameter of microemulsion droplets calculated using the proposed equation differ by no more than 1 nm from the values obtained by dynamic light scattering. Values of the droplet diameter of microemulsion in the DEHPA – decane – water system calculated using this equation are underestimated by 1.0-2.5 nm relative to the experimental values, while the slope of the lines obtained from the experimental data and during the calculation is almost the same.