Dynamic light scattering study of AOT microemulsions with nonaqueous polar additives in an oil continuous phase

Microemulsions with entrapped nonaqueous polar solvents-glycerol (Gly), ethylene glycol (EtGy), and formamide (Form)-and an oil (isooctane or n-heptane) continuous phase were studied by dynamic light scattering (DLS). The largest hydrodynamic radii evaluated for the two former systems, by the method of extrapolation to infinite dilution, were respectively 56.5 and 28 Angstrom. The method was not applicable to the latter system (formamide), making the determination of the hydrodynamic radius impossible. It was found that, in these microemulsion systems, the interactions between the droplets are more attractive than the ones observed in water-in-oil microemulsions, being larger in formamide and smaller in glycerol. The droplet structure remains spherical, but evidence of clusters was obtained in all the systems studied. Their formation is attributed to strong attractive interactions.