Time-resolved small-angle neutron scattering as a lamellar phase evolves into a microemulsion

Abstract

Time-resolved small-angle neutron scattering (SANS) was used to follow the formation of a microemulsion after rapid stopped-flow mixing of a lamellar phase (Lα), comprising the non-ionic surfactant TX-100 and water, with toluene. Initially after mixing, an oil-swollen Lα phase was formed. Between 4 and 160 s the Lα system evolved into a dense water-in-oil (w/o) microemulsion, during which time the two phases coexisted. After 160 s, the system was a pure single-phase microemulsion. SANS spectra were fitted using a linear combination of the phenomenological Teubner–Stey microemulsion and the Nallet lamellar models. The characteristic repeat distance of water domains in the microemulsion was seen to decrease over the first 70 s of the transformation as more of the microemulsion formed; conversely the domain correlation length appeared to increase.