Multiple Wetting–Dewetting States of a Water Droplet on Dual-Scale Hierarchical Structured Surfaces

Abstract

Surfaces with microscale roughness can entail dual-scale hierarchical structures such as the recently reported nano/microstructured surfaces produced in the laboratory ( 32494077 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 ( H 1 ), and the spacing between nanotextures ( W 1 ). Notably, E in – H 1 and E in – W 1 diagrams show that regions of rich wetting/dewetting states can be identified, including regions where between one to five states can coexist.

Molecular Simulation Study on the Wettability of a Surface Texturized with Hierarchical Pillars

“…Superhydrophobic surfaces find wide applications including anti-icing [1], anti-frosting [2], water collection [3], oil-water separation [4], drag-reducing [5,6], self-cleaning [7], prevention of corrosion [8,9], solar cells [10,11], and light-emitting diodes [12,13], just to name a few. Over the years, the wettability of a pillared surface has been extensively studied both experimentally [3] and theoretically [14][15][16][17]. Researchers have explored surfaces texturized with pillars that are diverse in shape and size.…”

Holistic Anti/Dewetting Design of Anti/Deicing Superhydrophobic Surfaces (ADISS)

“…Notably, even if the impacting droplet might invade the microtroughs when the water hammer pressure exceeds the antiwetting capillary pressure, they can still bounce off due to the maintenance of the nano-Cassie state (Section S3, Figure S10). ,, Additionally, this multiscale nonwetting state is of great significance for anti-icing properties in an icy environment. As shown in Figures b, c, and S11, the condensation droplets/frost on the STPL surface at ∼−10° can be removed by water droplets or jet impact without liquid adhesion, showing excellent microscopical antiwetting performance (Movies S2, S3).…”