Water solubilization capacity, interfacial compositions and thermodynamic parameters of anionic and cationic microemulsions

The water solubilization capacity of a particular microemulsion depends upon the partitioning of cosurfactants among water, oil and interfaces, chain length and nature of oil and cosurfactant, and their interaction with surfactant. Maximal water solubilization of microemulsion systems has been investigated by titration method. The interfacial compositions and associated thermodynamic parameters of the formation of microemulsion droplets have been studied by dilution method. The Bansal, Shah, O’Connell (BSO) equation has been verified by determination of solubilization capacity of microemulsion. Among the alkanes (C6–C18) employed in this work, maximal water solubilization for sodium dodecyl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB) microemulsion systems with cosurfactant (pentan-1-ol, and 3-methyl-1-butanol) have been found in case of heptane and undecane respectively. A correlation between the change in free energy of cosurfactant transfer at the interface and the alkane carbon number was examined. With increase in oil chain length, the negative value of the change in Gibbs free energy of cosurfactant transfer decreases.

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► Water solubilization capacity of microemulsion depends on molar volume of oil.
► According to BSO equation heptane and undecane show maximum water solubilization.
► Straight chain alcohol has higher water solubilization capacity.
► With increase in alkane carbon number −ΔGt° decreases.
► Compensation temperature is in range of experimental temperature.