Structure of Mixed Reverse Microemulsions Based on Sodium Bis (2‐Ethylhexyl) Sulfosuccinate and Sodium Cholate

Abstract

AbstractThe microenvironment of water droplets of sodium bis (2‐ethylhexyl) sulfosuccinate (AOT) and sodium cholate mixed reverse microemulsions was studied. Structural changes of water pockets in mixed reverse micelles were investigated by IR spectroscopy. The O‐H stretching vibrational absorption spectra in the region of 3000–3800 cm−1 were fit to three subpeaks with the Monte Carlo method. It was revealed that additives of sodium cholate suppress free water fraction in the water droplets of reverse micelles from 31% to 20% and support rising of bound fraction from 53% to 65%. The binding of optical probe ortho‐nitroaniline to the mixed reverse micelles was determined by UV–visible spectroscopy. It was found that introducing of additives of sodium cholate below its critical micelle concentration (CMC) causes increasing of values of binding constant Kb twice compared with reverse micelles modified with pure water. However, values of the binding constant were reduced 4‐fold at concentrations of sodium cholate higher than its CMC. Electrical conductivity of the reverse mixed micellar solutions (AOT + sodium cholate) was measured. Water‐induced percolation in conductance of mixed reverse microemulsions occurs at a lower value of water/surfactant molar ratio (W) under the influence of sodium cholate, viz. electrical percolation threshold decreases from W = 32 to W = 15. The size of water droplets was estimated with the dynamic light scattering method. It was found that additives of sodium cholate below and higher than the CMC results in increasing and decreasing of hydrodynamic diameters of the water droplets, respectively, but sizes of water droplets decrease at concentrations of sodium cholate higher than its CMC.