Adjusting droplet adhesion of superhydrophobic coating via surface embedding of microparticles with mixed shapes

Abstract

Designing intelligent superhydrophobic surfaces with versatile surface properties has garnered scholarly attention in field of heterogeneous catalysis, lab-on-chip, water harvesting, etc. However, the precise modulation of fluid adhesion on superhydrophobic surfaces, particularly when being applied as coatings, remains a challenge. Here we employ a “glue + powder” method for the fabrication of superhydrophobic surfaces with tunable droplet adhesion by embedding microparticles with mixed shapes. By adjusting the mixing ratio of rod-like and spherical particles, the sliding angle of superhydrophobic coating can be facilely controlled as well as the underwater bubble holding ability. During the dewetting process, the difference in the contact line lengths between micro-rod and micro-sphere contributes to the varying droplet adhesive force from 43.7 μN to 109.4 μN, which corresponds to the sliding angle change of a 10 μL droplet from 9.6° to 45.7°. Furthermore, by mixing fumed silica with branched structure, the lowest range of the rolling-off angle adjustment can be extended down to 0.5°, showing a precise and universal strategy for tuning the surface adhesion. On the basis of the meticulous manipulation of surface adhesion, controlling processes of single droplet and droplets accumulation can be fulfilled, with implications for enhancing the functionality of current superhydrophobic materials. Taking the advantage of the convenient and reliable fabrication method, a series of demonstration including manual droplet holders, multi-tiered droplet capturing interface, droplet sieving platforms, and gravity-driven droplet reactors has been realized. We envision that the precise control of droplet adhesion on superhydrophobic materials should further provides substantial opportunities for innovating fluid manipulation systems possessing heightened operability and multifunctionality.