AEROSOL-OT REVERSED MICELLAR FORMATION AT LOW WATER-SURFACTANT RATIO STUDIED BY SYNCHROTRON-RADIATION SMALL-ANGLE X-RAY-SCATTERING

By using synchrontron radiation small-angle X-ray scattering, we have studied the structure of biologial buffer/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/2,2,4-trimethylpentane (isooctane) reversed micelles with varying water-surfactant molar ratio omega(0) (=[H2O]/[AOT]), AOT concentration, and temperature. The scattering data were analyzed by several methods, including a shell modeling. Although in a high omega(0) range (16 < O-0 < 50) the obtained structural parameters of the AOT reversed micelle and the linear relation between the water pool radius and the omega(0) value are mostly in agreement with those determined by other authors, for 0 < omega(0) < 12, however, discrepancies were found, These deviations can be understood by a transient oligomerization of reversed micelles, where with the increase of water content the micellar oligomerization proceeds successively from a metastable oligomeric phase to a stable monomeric phase through a transient phase, Increasing the AOT concentration and/or temperature reduced the reverse micellar dimension.