Small-angle neutron-scattering study of microemulsions stabilised by aerosol-OT. Part 1.—Solvent and concentration variation

Abstract

Small-angle neutron-scattering (SANS) measurements have been made for a series of aerosol-OT (AOT)-stabilised water-in-oil microemulsions. The intensity pattern has been used to extract a value for the radius of the water core, r_w, using D₂O to provide the required contrast profile. In heptane the radii are found to follow an approximately linear relationship with respect to the [D₂O]/[AOT] concentration ratio, R. At 20 °C, and R= 20, the structure of the water-droplet system is dependent on the hydrocarbon chain length of the oil medium. The experimental SANS patterns show increasing discrepancies with a fitted function based on monodisperse spheres as the length of the alkane chain is increased from n-heptane to n-dodecane. This effect is attributed to polydispersity and indicates that the droplet-size distribution within these microemulsion systems is much larger than had previously been thought.