Formation of reverse micelles in supercritical carbon dioxide and its thermodynamics

The solubilization behavior of methyl orange as a solvation probe in multiple systems composed of super-critical carbon dioxide,surfactants and co-solvents,is studied.It is concluded that some surfactants,such as sodium bis-(2-ethylhexyl)sulfosuccinate(AOT)and isooctyl phenol polyethoxylate(TX-10),could form reverse micelles in supercritical carbon dioxide under the action of butanol.The formation of reverse micelles is a spontaneous process thermodynamically.Specifically for the nonionic surfactant TX-10,the formation of reverse micelles is dependent on the entropy increase in the system,while for the anionic sur-factant AOT,the micellization is mainly dominated by the increase in enthalpy at higher temperatures,but by the increase in entropy at lower temperatures.