Understanding surface wettability: insights from experiments, molecular simulations, and first-principles theory.

Wettability plays a central role in surface science with far-reaching implications for engineering technologies, biomedical applications, and natural systems. Despite decades of investigation, wettability research remains fragmented across experimental characterization, molecular dynamics simulations, and quantum mechanical calculations, with no unified framework linking observations across length and time scales. This fragmentation originates from inconsistencies in experimental protocols, force field parameterization strategies, and electronic structure descriptions, which have contributed to long-standing debates regarding the intrinsic wetting behavior of many technologically relevant surfaces. This review critically synthesizes advances in experimental measurements, atomistic simulations, and first principles modeling to identify areas of agreement, unresolved controversies, and persistent knowledge gaps in wettability research. Emphasis is placed on the breakdown of classical wetting models at nanometric scales, the non-uniqueness of the contact angle as a sole wettability descriptor, and the role of complementary thermodynamic, structural, and dynamic quantities in characterizing solid-liquid affinity. The review examines how interfacial modeling choices, including surface preparation, interaction potentials, mixing rules, and electronic structure approximations, systematically influence predicted wettability and contribute to inconsistent conclusions across studies. By integrating interfacial chemistry, molecular-scale structure, and macroscopic observables, this work provides a conceptual roadmap for designing wettability studies that are more consistent, reproducible, and predictive across methodologies and length scales.