Spontaneous transition of a water droplet from the Wenzel state to the Cassie state: a molecular dynamics simulation study

Abstract

It is widely accepted that the superhydrophobic state is attributed to the formation of the Cassie state. The Cassie state is mostly metastable, which can be turned into the Wenzel state. Therefore, the superhydrophobic state is generally considered to be unstable. In this study, the wetting behaviors of a water droplet on different pillar surfaces are simulated. The spontaneous transition from the Wenzel state to the Cassie state is achieved, which is significant for the stable existence of superhydrophobicity. The transition process is analyzed in detail and can be chronologically divided into two stages: the contact area decreases and the water droplet rises. Moreover, the transition mechanism is studied, which is due to the combined effect of the surrounding pillars and the central pillar. The surrounding pillars form a no-wetting gap under the droplet, and the central pillar forces the droplet to move upward. Furthermore, three parameters that may influence the transition are studied: the pillar height, the droplet size and the hollow size.

Characterizing the bifurcating configuration of hydrogen bonding network in interfacial liquid water and its adhesion on solid surfaces

“…It has been shown that decreasing 3 SL can effectively enhance surface hydrophobicity and this method has been widely used in previous studies. 34,35 All of our MD simulations were carried out on Gromacs 5.1.2. 36 Provided that the realistic density of liquid water is 996.5 kg m À3 at 300 K, there were 15 300 water molecules included in the modeling domain.…”

Mechanism Study on Transition of Cassie Droplets to Wenzel State after Meniscus Touching Substrate of Pillars

“…The hierarchical textures can be manufactured with photolithography and deep reactive-ion etching technology 39 . [42][43][44][45] . And the results of MDS is in consistence with the experiments in many aspects [42][43][44] .…”

Monostable superrepellent materials

“…In this context, it is worth exhibiting monostable Cassie states where even an accidental transition to the undesired Wenzel state, due to force fluctuations such as encountered in an impact (37) or to pressure applied on the liquid (16,17,33,(46)(47)(48)(49)(50), can be repaired owing to the absence of barrier between both states. Because reported Wenzel-to-Cassie (W2C) transitions generally involve either an external energy input (17,49,(51)(52)(53) or a potential energy release (35,(54)(55)(56), monostable Cassie states might be seen as unreal (57), but we describe here such situations and criteria for achieving them. Our hope is that these findings will shed new light on our fundamental understanding of water repellency.…”