SMALL-ANGLE NEUTRON-SCATTERING FROM NOVEL BIS-2-ETHYLHEXYLSULPHOSUCCINATE MICROEMULSIONS - EVIDENCE FOR NONSPHERICAL STRUCTURES

We report SANS measurements on water-in-oil (w/o) microemulsions stabilised by surfactants of the type M(n+)(AOT)n where AoT is bis-2-ethylhexylsulphosuccinate. The counterion M(n+) is from the series Na+, Ca2+, Mg2+, Co2+, Ni2+, Zn2+ and Cd2+. At low volume fractions of dispersed phase (phi(d) less-than-or-equal-to 0.05) and low added water content (w = [H2O]/[AOT] = 5.0) the SANS form factor P(Q) varies with M(n). The results show that for these compositions the microemulsion droplets with Na+ and Ca2+ are spheres whilst Co2+, Ni2+, Cu2+, Zn2+ favour rods. For Mg2+ and Cd2+ structures of intermediate shape are present.