Wetting Transition of Water on Monolayer Coated Materials

When three phases meet, interfacial interactions can favor either coexistence (partial wetting) or the elimination of one interface (complete wetting), with slight changes in environmental variables tipping the balance and triggering what is known as a wetting transition. Such transitions in systems dominated by long-range forces are typically predicted to be first-order, with continuous transitions considered as exotic phenomena far below the critical temperature Tc. Here we report the observation of a first-order wetting transition for water on monolayer graphene epitaxially grown on 4H–SiC, and the substrate itself, by direct visualization of the solid-liquid interface along liquid–vapor coexistence as temperature approaches ∼ 500K. Re-analysis of literature data further reveals continuous wetting transitions much below Tc on graphite, quartz, and sapphire, challenging established theory. These findings suggest that higher-order wetting transitions of water, though rare, may occur more widely under specific conditions. Wetting data is analyzed using a Lifshitz-van der Waals free energy model and a perturbative analytic approach adapted from cryogenic systems, enabling predictions of room temperature contact angle (RTCA) and the wetting transition temperature (Tw) for composite substrates. While the model predicts non-universality of wetting translucency, it finds RTCA to within 10% of the experimental value for various two-dimensional materials including WS2, MoS2 grown on common substrates.