Solvent effects on reverse micellisation of Tween 80 and Span 80 in pure and mixed organic solvents

Abstract

Reverse micellisations of nonionic surfactants (Tween 80 and Span 80) in various pure nonaqueous solvents like carbontetrachloride, benzene, toluene, chloroform, cyclohexane and xylene, and in mixed solvent systems like CC14-DMF and CC14-DMSO covering the low dielectric range, are studied by UV electronic spectroscopy at 25C. Micellar aggregation number (ns) in various solvents is evaluated using the hydrophobic dye, Oil Red. 0. The critical micellar concentration (cmc) and ns dependencies on the solvent dielectric, solvent ionization potential, solvent-surfactant interaction potentials, mole fractions of solvents in mixtures and internal pressures are studied. The CC14-DMSO system shows a cmc increase effect, while the CC14-DMF system shows a cmc decrease effect and the excess functions of CC14-DMSO and CC14-DMF show increase and decrease effects respectively. Rationalisations of the results and the role of the solvent cage effect have been discussed.