Small-Angle X-Ray and Neutron Scattering Applied to Emulsion: Recent Progress and Prospect

As a complex multiphase system, emulsions play a pivotal role in the pharmaceutical, food, and petroleum-production industries. Their macroscopic physical properties, such as rheological behavior, stability, and lubricity, depend strongly on the structure and properties of the oil-water interfacial films and on the structural evolution they give rise to from the nanometer to the micrometer scale. Owing to their non-destructive, in-situ, contrast-matching, and volume-averaging capabilities, small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) have become core tools for resolving emulsion structures. This review provides a targeted, in-depth discussion of the applications of SAXS and SANS to emulsion research in drug delivery, food science, and petroleum production. The use of small-angle scattering to resolve the interfacial composition, topology, and evolution of various emulsions is elaborated, and the physical modeling of interfacial structures and bicontinuous microemulsions is discussed. In addition, several cutting-edge advances are highlighted, such as time-resolved small-angle scattering (TR-SAXS/SANS) for tracking aggregation and oil-transport dynamics, spin-echo small-angle neutron scattering (SESANS) for structure analysis at large length scales, and in-situ multi-technique coupling with rheology (e.g., Rheo-SANS). Finally, we outline future directions in this field and discuss the great potential of combining new-generation neutron and photon sources with machine-learning-driven data analysis in both fundamental research and application development.