MICROSTRUCTURE IN A TERNARY MICROEMULSION STUDIED BY SMALL-ANGLE NEUTRON-SCATTERING

The microstructure in a ternary microemulsion, composed of pentaethyle ne glycol dodecyl ether (C(12)E(5)), water, and decane, was investigat ed by small angle neutron scattering along a dilution line defined by a constant surfactant-to-oil ratio, phi(s)/phi(o) = 0.815, where phi(s ) and phi(o) are the surfactant and oil volume fractions, respectively . In the experiments three different contrasts were applied and the co ncentration was varied in the range 0.02 not less than or equal to phi less than or equal to 0.22, where phi = phi(s) + phi(o). At lower tem peratures the microemulsion phase coexists with excess oil (emulsifica tion failure). Along the emulsification failure phase boundary the res ults are consistent with a structure of spherical oil droplets, the si ze of which do not change with concentration. A simultaneous fit to th e three different contrasts gives a droplet hydrocarbon radius of [r(h c)] = 75 Angstrom and a relative polydispersity sigma/r(hc) = 16%. Whe n increasing the temperature, data are consistent with an increase in micellar size and a deviation from spherical shape.