Manufacturing of mushroom-shaped structures and its hydrophobic robustness analysis based on energy minimization approach

Abstract

The construction of stable hydrophobic surfaces has increasingly gained attention owing to its wide range of potential applications. However, these surfaces may become wet and lose their slip effect owing to insufficient hydrophobic stability. Pillars with a mushroom-shaped tip are believed to enhance hydrophobicity stability. This work presents a facile method of manufacturing mushroom-shaped structures, where, compared with the previously used method, the modulation of the cap thickness, cap diameter, and stem height of the structures is more convenient. The effects of the development time on the cap diameter and overhanging angle are investigated and well-defined mushroom-shaped structures are demonstrated. The effect of the microstructure geometry on the contact state of a droplet is predicted by taking an energy minimization approach and is experimentally validated with nonvolatile ultraviolet-curable polymer with a low surface tension by inspecting the profiles of liquid–vapor interface deformation and tracking the trace of the receding contact line after exposure to ultraviolet light. Theoretical and experimental results show that, compared with regular pillar arrays having a vertical sidewall, the mushroom-like structures can effectively enhance hydrophobic stability. The proposed manufacturing method will be useful for fabricating robust hydrophobic surfaces in a cost-effective and convenient manner.

Re‐Entrant Microstructures for Robust Liquid Repellent Surfaces

“…Reproduced (Adapted) with permission. [ 20 ] Copyright 2017, American Institute of Physics (AIP) Publishing.…”

“…Wang et al developed a simple double photolithography followed by PDMS casting technique to fabricate mushroom-like PDMS microarrays without silicon micromachining and etching. [20] Figure 8B schematically shows the fabrication steps of this technique. In contrast to reliance on the timing of wet or dry etching, the advantage of this fabrication technique is the precise control of the geometrical parameters of the mushroom-like pillars during the photolithography processes.…”

“…Some other groups conducted the same method of measuring CA and CAH since it is a simple yet effective way to assess the wetting behavior of the re‐entrant structures. [ 20,24a,58 ]…”

“…For instance, Wang et al placed the droplets of a UV-curable resin with low surface tension on top of the fabricated mushroom-like structures and used SEM to observe the wetting states, especially the meniscus at the liquid-solid interface. [20] The main concern was that the resin droplets contracted after UV exposure and during solidification. This might adversely affect the accuracy of this technique to capture the true wettability of uncured polymers.…”

“…Pillars with mushroom-like structures tend to improve this stability better than those with concave, spherical, or flat tips. [20] The underlying reason is that the net force directed upward competes with the internal pressure so that surfaces do not get wet, thanks to the tip formed on the top of the mushroom-like structure. [21] Oleophilic surfaces can attract oils or organic liquids.…”