Effect of nano-pillared surfaces with an arrangement density gradient on droplet coalescence dynamics

Abstract

The ability to predict and control the coalescence of droplets is of great importance for both industrial and technological applications, including 3D printing, micro-cladding, and self-assembly. Here, a textured surface decorated with nano-pillared arrays was designed and its arrangement density (f) was found to significantly affect the coalescence dynamics of droplets through changing their wettability. A large arrangement density f of the nano-pillared arrays would induce a Cassie wetting state for droplets, which supports the coalescence process. But when decreasing f to a value that produces a Wenzel wetting state, the coalescence is heavily impeded by the nano-pillars. However, a very small arrangement density f is also favorable for coalescence because the pinning effect resulting from the nano-pillars becomes ignored. More importantly, special substrates were well designed by nano-pillars with a density gradient in order to control the coalescence dynamics for some potential applications. This work helps to shed light on the coalescence dynamics of droplets on a microtextured surface modified with different arranged nano-pillars and thereby provides guidance on how to control their behaviors.

The Effect of Surface Wettability and Coalescence Dynamics in Catalytic Performance and Catalyst Preparation: A Review

“…The use of pillared structure on the modified surface can not only tune the wettability of liquids but also significantly affect the coalescence dynamics. More recently, the effect of arrangement density ( f ) of nano‐pillared structures on the coalescence dynamics has been reported . As shown in Figure a, the nano‐pillared surface is built by the vertical VCNTs, and the f of the nano‐pillars is calculated as [Eq.…”

“… (a) Schematic illustration of the nano‐pillared surface, d , h and D represent the interval distance, height and diameter of nanopillars, respectively, (b) coalescence behaviours of Pb droplets on the surfaces with different f , and the graph denotes the coalescence time as a function of f , (c) coalescence behaviours of Pb droplets on the surfaces with different ∇ (0.5 Å, 1 Å, 2 Å), ∇=d′′–d′, (d) coalescence behaviours of Pb droplets on the “sparse‐dense‐sparse (SDS)”, and “dense‐sparse‐dense (DSD)” substrates . Reproduced with permission from Ref.…”

Controllable Coalescence Dynamics of Nanodroplets on Textured Surfaces Decorated with Well-Designed Wrinkled Nanostructures: A Molecular Dynamics Study

“…Given that, the coalescing behaviors of two droplets, both on the rough surfaces modified with nanopillared structures, have been studied. 24 The results suggested that with decreasing the arrangement density of the nanopillars, a wetting transition from the "Cassie model" 25 to the "Wenzel model" 26 was observed, which is unfavorable to the coalescence process. However, when the arrangement density decreases to a very small value, the coalescing process is rather supported because the restriction effect resulting from the pillared nanostructures becomes weakened.…”

“…In their work, however, only one drop is placed on the textured surface, while the other is stationary on the smooth surface, which is less influenced by the surface structure. Given that, the coalescing behaviors of two droplets, both on the rough surfaces modified with nanopillared structures, have been studied . The results suggested that with decreasing the arrangement density of the nanopillars, a wetting transition from the “Cassie model” to the “Wenzel model” was observed, which is unfavorable to the coalescence process.…”

A minimum energy optimization approach for simulations of the droplet wetting modes using the cellular Potts model

“…1 Functional surfaces with different wetting modes have applications in many areas such as superhydrophobic, 2,3 liquid directional transport, [4][5][6] oil-water separation, [7][8][9] and anti-icing. 10,11 The periodical grooved surface is a typical object to study the effects of factors such as dimensions, surface energy, 12 and scale of the pillar array [13][14][15] on wetting modes. Several methods or models were used to study the wetting phenomenon of the periodical grooved surface, such as the molecular dynamics simulation, 16,17 the continuum model, 18,19 the string method, 20 and the Cellular Potts Model (CPM).…”