Condensation and Wetting Transitions on Microstructured Ultrahydrophobic Surfaces

Abstract

On rough surfaces, two distinct wetting modes can appear. These two states are usually described by the theories of Cassie (drops suspended on top of roughness features) and Wenzel (drops impaled on roughness features). Whereas the wetting transition from the Cassie to the Wenzel state has been relatively well studied both experimentally and theoretically, the question of whether metastable Wenzel drops exist and how they transition to the Cassie state has remained open. In this work, we study the wetting behavior of microstructured post surfaces coated with a hydrophobic fluoropolymer. Through condensation, the formation of metastable Wenzel droplets is induced. We show that under certain conditions drops can transition from the Wenzel to the Cassie state.

An introduction to superhydrophobicity

“…On many surfaces this energy barrier is large enough that a drop of water will tend to stay in the state that it is put in (the Cassie-Baxter bridging state for a drop applied from the top) unless forced into the other state. A condensing liquid will always form in contact with the surface so droplets forming this way often begin in the Wenzel state and can be trapped there by the energy barrier in the same way that droplets deposited gently onto the surface will start in the Cassie-Baxter state [44]. The way that water condenses on superhydrophobic materials is of particular interest, because of its potential use in condensers [45,46].…”

Water condensation on zinc surfaces treated by chemical bath deposition

“…In contrast, and although this process is of major importance for the evaluation of corrosion, the studies of condensation-induced wetting on superhydrophobic surface and their corresponding wetting properties (self-cleanliness, different wetting states), are much less documented [18][19][20][21][22][23][24][25][26][27][28][29]. The aim of the present work is thus to study condensation of water on a multiscale rough superhydrophobic surface where the contact angle is varied in a wide range (70-150 • ).…”

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…Different from traditional superhydrophobic surfaces, which are characterized by the bouncing or rolling off of deposited millimeter-size large drops, [32,33] CMDSP surfaces support the self-removal capability of smallscale condensate microdrops. It has been reported that classical superhydrophobic lotus leaves (Figure 1a), [34][35][36][37] as well as artificial surfaces consisting of hierarchical micro-and nanostructures, [38] one-tier microstructures, [39][40][41][42][43] or nanostructures [44,45] with larger characteristic interspaces, present a low-adhesivity property to the deposited water macrodrops, but become highly adhesive to condensed microdrops (Figure 1b). This is because moisture easily penetrates the microscale valleys or cavities.…”