Molecular Mechanisms of Solvation Force for Aqueous Systems

Solvation force, stemming from the interfacial liquid structure, dominates the short-range interfacial interaction within a few nanometers across broad fields such as battery, lubrication, and colloid. However, achieving a quantitative understanding of solvation force for an aqueous system has remained elusive for decades, with the widely used contact value theory underestimating solvation force due to inherent assumptions. In this work, inspired by the flow field of liquid when two confining surfaces approach each other, we proposed a parameter-free expression for the solvation force acting on atomically smooth surfaces, quantitatively related to the energy barrier when liquid molecules are squeezed out from confinement. The effects of temperature and wetting properties of the surface on solvation force curves are found to be different. Solvation force measured by three-dimensional atomic force microscopy (3D-AFM) validates theoretical prediction on three types of surfaces ranging from hydrophilic to hydrophobic and reveals that the energy barrier is more intrinsic than density.