Wettability of graphene

Many far-reaching applications of graphene require a deep understanding of the interactions between graphene and other surfaces, including the wetting behaviour of graphene. However, its two-dimensional nature does not allow qualifying graphene as simply hydrophobic or hydrophilic, but instead gives rise to a diversity of interfacial phenomena governing the apparent wettability of graphene. As a result, wide disparities in the wetting properties of graphene have been widely reported. In this review we analyse the wettability of graphene with a special focus on the experimental conditions and on discriminating the causes of the reported inconsistencies. The elimination of the environmental factors causing misleading data is a major challenge. Importantly, progresses made in graphene research yielded new experimental insights and tools enabling the minimization of unwanted effects and, ultimately, the achievement of reliable contact angle measurements. Besides the macroscopic wettability studied using contact angle measurements under ambient conditions or by theoretical modelling, we also analysed correlations with the wettability of graphene at the molecular level in supremely pure environment of ultra-high vacuum.