SMALL-ANGLE NEUTRON-SCATTERING FROM DILUTE DIDODECYLDIMETHYLAMMONIUM BROMIDE WATER-IN-OIL MICROEMULSIONS - EVIDENCE FOR POLYMER-LIKE AGGREGATES

The structure of water-in-oil (w/o) microemulsion aggregates formed by didodecyldimethylammonium bromide (DDAB) at.volume fraction phi(d) (=[V(surf) + V(H2O)]/V(tot)) less than 0.03 has been determined by small-angle neutron scattering (SANS). For w (=[H2O]/[DDAB]) values less than 7.0 the SANS profiles are consistent with a system of polymer-like microemulsion aggregates. In this composition regime the scaling behavior of the radius of gyration of the aggregates R(g) with volume fraction is in agreement with recent theory. As w is increased to 10.0 a structural change occurs and spherical droplets with a mean radius of 36 angstrom are present. These observations highlight the very different types of structures that can occur in the L2 phase and are also in agreement with the current theory.