Visualization of Graphene on Various Substrates Based on Water Wetting Behavior

Graphene has unique water wetting properties, which have drawn great research interests recently. On the other side, water condensation and evaporation is a natural phenomenon in our daily life. Here, by combining the wetting properties of graphene and water condensation, a facile optical visualization approach is developed for graphene on a variety of substrates simply with the assistance of water vapor. Monolayer graphene becomes optically visible in several seconds with bellowing of water vapor. The wetting properties of monolayer graphene-covered surface and uncovered surface on various substrates, including copper, pristine silicon (Si), HF-treated Si, SiO2/Si, quartz, glass, polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), and micropatterned PDMS, are studied. It is shown that graphene is visible when it is not fully transparent to wetting for the underlying substrates. The different wetting behavior of graphene-covered and uncovered surface leads to the difference in the distribution and morphology of water droplets, also gives rise to the interesting confining wall effect of the graphene edge, contributing to the observation of graphene. Moreover, this approach also enables distinguishing the monolayer and nonmonolayer graphene. This simple but powerful method is green, convenient, and repeatable, promising its great potential applications for graphene or other 2D materials.