Microstructure in a Ternary Microemulsion Studied by Small Angle Neutron Scattering

Abstract

The microstructure in a ternary microemulsion, composed of pentaethylene glycol dodecyl ether (C12E5), water, and decane, was investigated by small angle neutron scattering along a dilution line defined by a constant surfactant-to-oil ratio, φs/φo = 0.815, where φs and φo are the surfactant and oil volume fractions, respectively. In the experiments three different contrasts were applied and the concentration was varied in the range 0.02 ≤ φ ≤ 0.22, where φ = φs + φo. At lower temperatures the microemulsion phase coexists with excess oil (emulsification failure). Along the emulsification failure phase boundary the results are consistent with a structure of spherical oil droplets, the size of which do not change with concentration. A simultaneous fit to the three different contrasts gives a droplet hydrocarbon radius of 〈rhc〉 = 75 A and a relative polydispersity σ/rhc = 16%. When increasing the temperature, data are consistent with an increase in micellar size and a deviation from spherical shape.