Fig. 3: Extrinsic tuning of wettability.

a (i) Schematic illustration showing graphene wettability modulation by doping-induced Fermi level shifts. (ii) WCA (left axis) measured by environmental scanning electron microscopy (E-SEM) and work function (WF, right axis) measured by scanning Kelvin probe microscopy (SKPM) of polyelectrolyte-doped and undoped graphene samples. For both n- and p-doping, the WCA of the graphene decreases. Insets show false-colored E-SEM images of the water droplets (scale bars represent 10 μm)³¹. b Snapshots of the water droplet spreading process under an electric field parallel to the graphene surface at (i) E = 0.2 V nm⁻¹, (ii) E = 0.4 V nm⁻¹, and (iii) E = 0.8 V nm⁻¹. The equilibrium system possesses a WCA of 62.7° at E = 0.2 V nm⁻¹. (iv) The height of the water droplets versus simulation time under various electric fields³³. c The tunable wettability of MoS₂ nanoflowers by manipulation of the microstructure. (i) Photos of as-transferred (upper panel) and crumpled (lower panel) MoS₂ nanoflowers on a polystyrene (PS) substrate. Scale bars: 1 cm. (ii) Schematic illustrations (upper panel) and SEM images (lower panel) of crumpled MoS₂ nanoflowers via thermal shrinkage of a PS substrate. Scale bars: 500 nm (lower left) and 100 nm (lower right). (iii) Tunable advancing/static/receding WCAs of MoS₂ nanoflowers as a function of macroscopic compressive strain. Triangles denote the #1 nanoflowers (the roughest), whereas circles represent the #3 nanoflowers (the flattest)⁴⁰. a Reprinted (adapted) with permission from Ashraf et al.³¹, Copyright (2016) American Chemical Society. b Republished with permission from the Royal Society of Chemistry from Ren et al.³³, permission conveyed through the Copyright Clearance Center, Inc. c Reprinted (adapted) with permission from Choi et al.⁴⁰, Copyright (2017) American Chemical Society.