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ABSTRACT
Thirteen kinds of AOT-metal surfactants (metal bis(2-ethyl hexyl)sulfosuccinate, MOT) were prepared by the metathesis of sodium bis(2-ethyl hexyl)sulfosuccinate (AOT) with the chlorides of transition, alkali, and alkaline earth metals. It was confirmed that bi- and trivalent MOTs are disoap and trisoap, respectively. The measurements of electric conductivity showed that the bond of SO∃ group in AOT molecule with the metals is ionic. The infrared spectra showed little coordination interaction of carbonyl groups with metal ions.
The aggregation number determined by the vapor pressure osmometry decreased with the increase in metal valence in cyclohexane and benzene. This was interpreted as the result that micelle formation for bi- or trivalent MOTs is disturbed by intermolecular steric hindrance between aliphatic chains extended toward two or three directions. The plots of the solubilizing power for water vs the ionic radius of metals showed that the surfactants are roughly classified into two groups, i.e., AOT and bivalent MOTs except for Ca-OT. But no clear correlation between the ionic radius and the solubilizing power was observed in comparison within bivalent MOTs. The morphologies of the aqueous dispersions of MOTs were examined by a polarizing microscope. Bivalent MOTs (Co-OT, Cu-OT, Mn-OT, and Ni-OT) showed anisotropic morphologies, but trlvalent MOTs (Fe-OT and Cr-OT) did not. The particle size of the aqueous dispersion of Co-OT was measured using the dynamic light-scattering method, being 440–750nm.