SOME AQUEOUS-SOLUTION AND SURFACE-PROPERTIES OF DIALKYL SULFOSUCCINATE SURFACTANTS

Ion exchange of sodium didodecyl sulfosuccinate to the lithium form produces a dramatic increase in aqueous solubility. Solutions of the lithium salt were studied using transmission electron microscopy which showed that stable, multiwalled vesicles formed spontaneously with an average size of 500-700 Angstrom. Some larger liposomal structures with a size of about 2000 Angstrom were also present. Individual bilayer spacings of about 35 Angstrom were observed via a negative staining technique. The effect of ion exchange on the head-group area was studied using the Langmuir-Blodgett technique. Exchange to the lithium form caused a 20% increase in head-group area. Another sulfosuccinate surfactant Aerosol-OT (AOT) for which both the sodium and lithium forms are soluble was used for a comparison of surface charge. Using microelectrophoresis, both the sodium and lithium forms of AOT were found to have similar surface charge densities. However, the slightly larger head-group area observed for the lithium form indicates an increase in counterion dissociation. These results suggest that it is the increased hydration of the lithium counterion that is responsible for increasing the headgroup area and hence change in aggregation state and solubility.