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Multiple Wetting–Dewetting States of a Water Droplet on Dual-Scale Hierarchical Structured Surfaces
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posted on 2021-06-24, 18:42 authored by Yurui Gao, Yuan Liu, Jian Jiang, Chongqin Zhu, Craig Zuhlke, Dennis Alexander, Joseph S. Francisco, Xiao Cheng ZengSurfaces with microscale
roughness can entail dual-scale hierarchical
structures such as the recently reported nano/microstructured surfaces
produced in the laboratory (Wang
et al. Nature 2020, 582, 55−57). However,
how the dual-scale hierarchical structured surface affects the apparent
wetting/dewetting states of a water droplet, and the transitions between
the states are still largely unexplored. Here, we report a systematic
large-scale molecular dynamics (MD) simulation study on the wetting/dewetting
states of water droplets on various dual-scale nano/near-submicrometer
structured surfaces. To this end, we devise slab-water/slab-substrate
model systems with a variety of dual-scale surface structures and
with different degrees of intrinsic wettability (as measured based
on the counterpart smooth surface). The dual-scale hierarchical structure
can be described as “nanotexture-on-near-submicrometer-hill”.
Depending on three prototypical nanotextures, our MD simulations reveal
five possible wetting/dewetting states for a water droplet: (i) Cassie
state; (ii) infiltrated upper-valley state; (iii) immersed nanotexture-on-hill
state; (iv) infiltrated valley state; and (v) Wenzel state. The transitions
between these wetting/dewetting states are strongly dependent on the
intrinsic wettability (Ein), the initial
location of the water droplet, the height of the nanotextures (H1), and the spacing between nanotextures (W1). Notably, Ein–H1 and Ein–W1 diagrams show that
regions of rich wetting/dewetting states can be identified, including
regions where between one to five states can coexist.
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