Atomic-Scale Variations of Interfacial Water Structure Driven by Site-Specific Chemistry

Although interfacial solution structure impacts environmental, biological and technological phenomena, including colloidal stability, protein assembly, heterogeneous nucleation, and water desalination, its molecular details remain poorly understood. Here, we visualize the three-dimensional (3D) hydration structure at the boehmite(010)-water interface using fast force mapping (FFM). Using a self-consistent scheme to decouple long-range tip-sample interactions from short-range solvation forces, we obtain the solution structure with lattice resolution. The results are benchmarked against molecular dynamics simulations that explicitly include the effects of the tip with different levels of approximation and systematically account for tip size, chemistry, and confinement effects. We find four laterally structured water layers within one nanometer of the surface, with the highest water densities at sites adjacent to hydroxyl groups. The findings reveal a complex relationship between site-specific chemistry, water density, and long-range particle interactions; and represent a major step forward towards quantitative data interpretation and widespread implementation of 3D FFM.