Beyond Core-Shell Micellar Structures: complex structures in simple surfactants

Small-angle X-ray/neutron scattering (SAXS/SANS) techniques provide valuable nanostructural information of self-assembling molecules. However, extracting the information from these experiments can be a challenging task, usually relying on predetermined assumptions. Conventional models for surfactant micelles consider a core-shell structure with a hydrophobic tail encapsulated by the hydrophilic part. This approach is successful in many cases, but can fail even for common surfactants such as Triton X-100 (TX-100). We employ SAXS and SANS combined with Metainference molecular simulations to investigate TX-100 assemblies, showing how more complex models, with diffuse core-shell boundaries, multilayering, and polydispersity, are needed to explain the aggregation. Compared to regular micelles formed by chemically similar C12EO10 molecules, we discuss the role of the hydrophobic core in micellization, finding that the relatively shorter and less hydrophobic tail of TX-100 favours polymorphism.