Small-angle neutron scattering differentiates molecular-level structural models of nanoparticle interfaces.

The highly anisotropic and nonadditive nature of nanoparticle surfaces restricts their characterization by limited types of techniques that can reach atomic or molecular resolution. While small-angle neutron scattering (SANS) is a unique tool for analyzing complex systems, it has been traditionally considered a low-resolution method due to its limited scattering vector range and wide wavelength spread. In this article, we present a novel perspective on SANS by showcasing its exceptional capability to provide molecular-level insights into nanoparticle interfaces. We report a series of experiments on multicomponent nanoparticles, where we demonstrate the ability of SANS to differentiate between competing structural models with molecular- and Å-scale differences. The results provide accurate quantification of organic ligand chain lengths, nanoparticles' heterogeneity, and detailed structures of surrounding counter-ion layers in solution. Furthermore, we show that SANS can probe subtle variations in self-assembled monolayer structures in different thermodynamic states. Our findings challenge the conventional view of SANS as a low-resolution technique for nanoparticle characterization and demonstrate its unique potential for providing molecular-level insights into complex nanoparticle surface structures.