Quantifying Å-Scale Non-Additive Solvation at Nanoparticle Interfaces

Solvent organization at solid-liquid interfaces dictates nanoparticle stability, catalysis, and self-assembly. Classical physical-chemistry theories commonly treat solvent quality as an additive continuum variable-an assumption increasingly questioned at the nanoscale but rarely experimentally quantified. Here, we address this challenge by combining small-angle neutron scattering (SANS) with Monte Carlo real-space reconstruction, allowing direct, molecular-level quantification of interfacial solvent structures under native solution conditions. In mixed solvents, we uncover discrete sub-nanometer solvent clusters whose abundance and spatial organization evolve non-linearly with solvent composition. These solvent clusters preferentially infiltrate nanoparticle ligand coronas, forcing ligand shells to deform from spherical symmetry into anisotropic ellipsoids-behavior that classical continuum core-shell models fail to describe. Interestingly, maximal solvent clustering, anisotropic deformation, and preferential solvent uptake coincide precisely at the bulk azeotropic composition, directly linking bulk solvent microstructure with nanoscale interfacial symmetry breaking. By turning a long-standing theoretical prediction into a quantitative measurement, this methodology establishes a versatile route for probing and ultimately tailoring solvation effects at a wide range of soft and hybrid interfaces.