Time-resolved SANS for surfactant phase transitions

Abstract

Surfactants spontaneously self-assemble in solution to form a variety of microstructures. Our understanding of the equilibrium properties of these aggregates, such as their shape and size, has made significant progress. However, only limited information is available on the kinetics and pathways of phase transitions and on the existence of non-equilibrium or metastable states. Fortunately, this unsatisfactory situation can now be overcome owing to recent developments in small-angle neutron scattering (SANS) instrumentation which significantly improve the temporal and spatial resolution. These new, fascinating possibilities are illustrated by two examples. Firstly, time-resolved SANS reveals the structure of the intermediate in a spontaneous transition from micelles to vesicles in aqueous mixtures of lecithin and bile salt. Secondly, a microemulsion containing spherical oil droplets is temperature quenched into a two-phase situation where excess oil separates out. The nucleation and growth of the separating oil droplets is, again, followed by time-resolved SANS.