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

Ion exchange of sodium didodecyl sulfosuccinate to the lithium form pr oduces a dramatic increase in aqueous solubility. Solutions of the lit hium salt were studied using transmission electron microscopy which sh owed that stable, multiwalled vesicles formed spontaneously with an av erage size of 500-700 Angstrom. Some larger liposomal structures with a size of about 2000 Angstrom were also present. Individual bilayer sp acings of about 35 Angstrom were observed via a negative staining tech nique. The effect of ion exchange on the head-group area was studied u sing the Langmuir-Blodgett technique. Exchange to the lithium form cau sed a 20% increase in head-group area. Another sulfosuccinate surfacta nt Aerosol-OT (AOT) for which both the sodium and lithium forms are so luble was used for a comparison of surface charge. Using microelectrop horesis, both the sodium and lithium forms of AOT were found to have s imilar surface charge densities. However, the slightly larger head-gro up area observed for the lithium form indicates an increase in counter ion dissociation. These results suggest that it is the increased hydra tion of the lithium counterion that is responsible for increasing the headgroup area and hence change in aggregation state and solubility.