The structure of water-in-oil microemulsions of sodium sulfosuccinate] was investigated by using FTIR spectroscopy. Two types of water were observed: interfacial and bulklike. The relative amounts are found to depend on the water-to-surfactant ratio and also on the solvent. Addition of salt was found to change the interactions between the interfacial water and the polar groups of AOT without changing the total amount of interfacial water.
Quasi-elastic light scattering was used to investigate W/O microemulsions of heptane-AOT-(bis(2-ethylhexyl)sulfosuccinate sodium salt)-water and W/O and O/W microernulsions of hexadecane-SDBS (sodium dodecyl benzene sulfonate)-n-pentanol-water systems as a function of temperature and dispersed-phase volume. The apparent molecular weights, distribution functions of radii, and diffusion coefficients were determined from the autocorrelation function of the scattered light. In the heptane-AOT-water system it was found that at constant temperature and constant AOT concentration the total interfacial area was independent of the water volume over a fairly large range. The polydispersity and the average hydrodynamic radii increased with temperature and disperse-phase volume for the W/O microemulsions. The average droplet radius ranged from 60 to 3000 ]k. The behavior of the O/W microemulsions was found to be more complex. In most of the 11 systems studied the distribution functions were bimodal, indicating the presence of surfactant micelles in equilibrium with microemulsion droplets. The apparent molecular weights determined from intensity measurements and from the average hydrodynamic radii agree well for the heptane-AOT-water systems but the agreement is not good for the other systems.
Interactions between the disperse phase droplets of water-in-oil (W/O) microemulsions of Aerosol-OT are profoundly affected by the addition of small amounts of electrolyte. We find that the effect of added electrolyte in W/O microemulsions is opposite to that which is observed in aqueous micellar solutions and O/W microemulsions, here the addition of electrolyte decreases attractive interactions rather than increasing them. Dynamic light scattering measurements show that the addition of salt decreases (and even eliminates) the dependence of the diffusion coefficient on disperse phase concentration. Time-averaged intensity measurements and shear viscosity measurements provide further evidence of increased hard-sphere-like behavior as the salt concentration increases. Analysis of the time-averaged intensity using a formalism developed by A. A.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.