Multiple Wetting−Dewetting States of a Water Droplet on Dual-scale Hierarchical Structured Surfaces

Authors

Yurui Gao, University of Nebraska-Lincoln
Yuan Liu, Sun Yat-sen University
Jian Jiang, University of Nebraska-LincolnFollow
Chongqin Zhu, Beijing Normal UniversityFollow
Craig Zuhlke, University of Nebraska-LincolnFollow
Dennis Alexander, University of Nebraska-LincolnFollow
Joseph S. Francisco, University of PennsylvaniaFollow
Xiao Cheng Zeng, University of Nebraska-LincolnFollow

ORCID IDs

Gao https://orcid.org/0000-0001-7486-8134

Liu https://orcid.org/0000-0002-8239-7704

Francisco https://orcid.org/0000-0002-5461-1486

Zeng https://orcid.org/0000-0003-4672-8585

Document Type

Article

Date of this Version

2021

Citation

JACS Au (2021) 1: 955−966

doi: 10.1021/jacsau.1c00183

Supporting information is available at https://pubs.acs.org/doi/10.1021/jacsau.1c00183?goto=supporting-info

Comments

Copyright 2021, the authors. Open access

License: CC BY-NC-ND 4.0

Abstract

Surfaces with microscale roughness can entail dualscale 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 (E_in), the initial location of the water droplet, the height of the nanotextures (H₁), and the spacing between nanotextures (W₁). Notably, E_in−H₁ and E_in−W₁ diagrams show that regions of rich wetting/dewetting states can be identified, including regions where between one to five states can coexist.