MICROSTRUCTURES IN THE SYSTEM WATER D2EHPA/SPAN-80/N-DODECANE/

The solubilization of water by the single ionic amphiphile bis(2-ethyh exyl)phosphoric acid (D2EHPA) and the single nonionic surfactant Span 80 in a nonpolar medium has been investigated. The hydrodynamic, optic al, and other various analytical techniques were extensively employed to study the physicochemical nature of the microstructures formed in D 2EHPA/n-dodecane/water and Span 80/n-dodecane/water solutions. An anal ytical model based on geometrical assumptions of the spherical shape o f the reversed micelles has been developed. The proposed model correla tes, among several others, the aggregation number, and, thus, the size of microstructures with parameters such as the hydrocarbon chain leng th of the surfactant molecule, its concentration and volume fraction o ccupied by the reversed micelles, etc., the latter is being estimated from the Einstein viscosity equation and its two modified versions rep orted by Guth and Simha and Vand. Assuming the spherical shape of the aggregates, the Einstein equation was found to fit the experimental da ta of the D2EHPA solutions very well; however, Vand's equation was fou nd to be more suitable to fit those of Span 80 solutions. The molecula r associates formed by D2EHPA were mostly dimers; however, relatively larger microstructures were formed by Span 80, the higher the concentr ation the smaller the size with a tendency to leveling off and the sha pe is nonspherical. The basic structural parameters, that is, the aggr egation number, reversed micelle, and water pool radii were derived, a nd a good agreement between the experimental and the predicted data fr om the model was found.