Can Excess-Entropy-Diffusivity Lens Reimage Wettability?

Breakdown in wetting transparency across micro/macroscopic scales remains a central challenge in understanding complex interfacial phenomena. Here, we present a molecular-level framework elucidating the wettability of atomically smooth and rough solid surfaces. From atomistic molecular dynamics simulations, we found that wettability can be fundamentally defined by the coupling between the in-plane molecular structure of the liquid phase and its mobility within the contact plane. This coupling is modulated by both the liquid–solid interaction strength and surface roughness. Surfaces exhibiting low wettability are characterized by reduced structural ordering and enhanced molecular mobility at the contact plane, whereas high wettability corresponds to increased ordering and low mobility. The transition between distinct wetting states manifests as a surface-induced phase transition within the interfacial contact plane, emerging with increasing liquid–solid interaction. In contrast, surface roughness significantly alters the extent of in-plane ordering and diffusivity, leading to a reduction in wettability relative to a smooth surface under identical interactions. Notably, this framework is inherently droplet-size-independent, identifying the in-plane molecular structure-dynamics correlation as the sole fundamental descriptor of wettability.