Liquid structure adjacent to solid surfaces follows the superposition principle

TL;DR

This study reveals a universal superposition principle governing liquid structures at solid-liquid interfaces, enabling accurate predictions across multiple scales using experimental imaging and a new analytical model.

Contribution

The paper introduces the solid-liquid superposition (SLS) model, a novel analytical framework that predicts interfacial liquid density profiles based on the effective total correlation function.

Findings

Universal liquid density oscillations observed at heterogeneous interfaces

SLS model accurately predicts atomic-scale interference patterns

Experimental and MD simulations validate the superposition principle

Abstract

Liquid structure at solid-liquid interfaces is critical for many natural and engineered processes ranging from biological signal transduction to electrochemical energy conversion. Advanced experimental and computational methods have provided insights into the structure of liquids adjacent to planar substrates at the nanoscale. However, realistic solid-liquid interfaces are inevitably inhomogeneous across multiple length scales, presenting a complexity that surpasses the capabilities of existing approaches. Here we bridge the complexity gap by discovering and utilizing a hitherto hidden principle of interfacial liquid--superposition. Experimentally, we use 3D atomic force microscopy (3D-AFM) to image the interfacial structure of a wide range of organic and aqueous solvents and electrolytes, uncovering universal liquid density oscillations and emergent liquid layer reconfigurations at heterogeneous substrate sites. We further develop an analytical model, coined solid-liquid superposition (SLS), which solves the interfacial liquid density distribution based on a key descriptor: the effective total correlation function (ETCF) between a liquid molecule and nearby solid atoms. SLS not only explains all the experimentally observed interfacial liquid distribution profiles from the angstrom to near-micron scale, but also predicts more precise atomic-scale interference patterns which are further corroborated by molecular dynamics (MD) simulations. This study unveils a key structural descriptor of interfacial liquids, and establishes a theoretical framework for rapidly and accurately predicting liquid structures adjacent to solid surfaces with arbitrary morphology and size scale.