Graphene supported on a substrate in contact with water underpins a wide range of processes and technologies, yet its wettability remains controversial. Understanding how substrate charges and graphene's properties influence water organization is crucial. Here, we combine heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy with molecular dynamics simulations to investigate CaF2-supported graphene interfaces in contact with water. We find that interfacial water orientation is primarily governed by the CaF2 substrate's pH-dependent local electrostatics, confirming graphene's macroscopic wetting transparency. However, at the nanoscale, graphene's polarizability induces a local inversion of water's molecular orientation above substrate charges, revealing subtle structural ordering that is masked in spatially averaged measurements. These insights elucidate the molecular origins of graphene's wetting behavior and suggest new avenues to tailor interfacial phenomena in graphene-based nanofluidic, sensing, and energy applications.
@article{arxiv.2511.04930,
title = {Wetting Transparency of Graphene: A macroscopic Window but Nanoscopic Mirror},
author = {Yongkang Wang and Yair Litman and Minhaeng Cho and Stephen Cox and Mischa Bonn},
journal= {arXiv preprint arXiv:2511.04930},
year = {2025}
}