Abstract
Molecular dynamics (MD) simulation has been employed to study the wetting transitions of liquid gallium droplet on the graphene surfaces, which are decorated with three types of carbon nanopillars, and to explore the effect of the surface roughness and morphology on the wettability of liquid Ga. The simulation results showed that, at the beginning, the Ga film looks like an upside-down dish on the rough surface, different from that on the smooth graphene surface, and its size is crucial to the final state of liquid. Ga droplets exhibit a Cassie–Baxter (CB) state, a Wenzel state, a Mixed Wetting state, and a dewetting state on the patterned surfaces by changing distribution and the morphology of nanopillars. Top morphology of nanopillars has a direct impact on the wetting transition of liquid Ga. There are three transition states for the two types of carbon nanotube (CNT) substrates and two for the carbon nanocone (CNC) one. Furthermore, we have found that the substrates show high or low adhesion to the Ga droplet with the variation of their roughness and top morphology. With the roughness decreasing, the adhesion energy of the substrate decreases. With the same roughness, the CNC/graphene surface has the lowest adhesion energy, followed by CNT/graphene and capped CNT/graphene surfaces. Our findings provide not only valid support to previous works but also reveal new theories on the wetting model of the metal droplet on the rough substrates.
Highlights
The stretchable electronics achieve remarkable progress in soft robotics [1,2,3], flexible devices [4,5,6,7,8], and especially the biological field [5,9]
Gallium is regarded as a promising alternative to the toxic mercury
Å wasnanopillars placed on the rough horizontal dimensions of 200 carbon (CCNTs)with
Summary
The stretchable electronics achieve remarkable progress in soft robotics [1,2,3], flexible devices [4,5,6,7,8], and especially the biological field [5,9]. Room temperature liquid metals have drawn increasing attention in state-of-the-art applications in these fields because the desirable materials involved are intrinsically soft and remain functionally stable when their morphology changes [1,6,7,9]. Gallium and their alloys, being in a liquid state at room temperature with high thermal and electrical conductivity, with low toxicity and evaporation pressure, make them ideal candidates for a myriad of applications. The effective combination of these two typical classes of Molecules 2018, 23, 2407; doi:10.3390/molecules23102407 www.mdpi.com/journal/molecules
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