Roughness-Induced Chemical Heterogeneity Leads to Large Hydrophobicity in Wetting-Translucent Nanostructures
JE Andrews and YB Wang and S Sinha and PW Chung and S Das, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 10010-10017 (2017).
Hydrophobic graphene marries the usefulness of graphene with the benefits of a hydrophobic surface leading to applications in oil water separation, wettability switching,, electromagnetic radiation shielding, fabrication of smart actuators and wearable electronics, tissue engineering, and many more. In current practices, such hydrophobicity in graphene or graphene-based materials or GBMs (e.g., graphene oxide) has been introduced by either chemical treatment or by enforcing graphene or GBM into a physical structure that triggers a hierarchical roughness enforcing the water drop into a Cassie Baxter (CB) state. Here, through molecular dynamics (MD) simulations, we describe a new route to graphene-based hydrophobicity. We demonstrate that the wetting translucency property of graphene ensures that the surface-periodic features such as nanopillars can trigger a roughness-induced chemical heterogeneity. Therefore, an uneven coating of graphene on a hydrophilic surface (e.g., gold) will lead to a chemical heterogeneity across this graphene coating. This heterogeneity, in turn, enforces a wettability jump that ultimately results in contact line pinning and triggering of large hydrophobicity. Influence of this hydrophobicity-triggering mechanism can be so significant that one may witness a highly hydrophobic, fully wetted Wenzel state that is equally as hydrophobic as the corresponding CB state.
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