Microdrop-Assisted Microdomain Hydrophilicization of Superhydrophobic Surfaces for High-Efficiency Nucleation and Self-Removal of Condensate Microdrops

Abstract

Superhydrophobic–hydrophilic hybrid surfaces have attracted intensive interest because of their significant academic and commercial values. However, almost all reported microdomain hydrophilicization methods rely on costly micropatterning techniques that need special instruments. Here, we report a microdrop-assisted method for microdomain hydrophilicization of a low-adhesive superhydrophobic surface and demonstrate its utility in high-efficiency nucleation and self-removal of condensate microdrops. Micrometer-sized fogdrops containing polyvinyl alcohol molecules can be selectively captured by breath figures of superhydrophobic surfaces with specific sizes and spatial distributions and can be converted into desired hydrophilic microdomains after thermal evaporation. After exploring the influence of hydrophilic microdomains’ distributions and sizes to surface wettability, adhesion, and condensation dynamics, we achieved an optimal hybrid surface, which possesses 240% average microdrop density, 387% microdrop self-removal rate, and 75% average microdrop diameter as compared to the contrast superhydrophobic surface with uniform chemistry nature. This method is dispensed with special equipment, easy to implement, very cheap, and eco-friendly, which would help develop other superhydrophobic–hydrophilic hybrid surfaces with different functions such as water harvesting, dehumidification, and heat exchange.

Nature-Inspired Structures Applied in Heat Transfer Enhancement and Drag Reduction

“…However, the condensation amount is small due to the high nucleation barrier. In contrast, the condensate droplets are difficult to separate on the hydrophilic surface, and the condensation amount is large due to the low nucleation barrier [51][52][53]. Therefore, it is reasonable to distribute and regulate the wettability of structures for reducing condensate droplets nucleation barrier and increasing nucleation density.…”

Advances in Dropwise Condensation: Dancing Droplets

“…To delay the occurrence of flooding for achieving stable jumping droplets, various superhydrophobic surfaces with closely spaced nanostructures (Figure 9a) have been recently proposed to spatially control nucleation [66,98,99]. Minimizing the spacings using high-aspect ratio nanowires can promote to obtain a vapor density difference between the inside and outside of the nanoscale spacing.…”

Large-scale efficient water harvesting using bioinspired micro-patterned copper oxide nanoneedle surfaces and guided droplet transport

“…As reported in the previous studies, the arrangement of the super-hydrophobic and superhydrophilic surfaces together in different orientations and patterns can further enhance the overall water collection ability of the surfaces. 12,20,51 So using these coated and non-coated nanoneedle-based surfaces, the creation of varying wettability patterns in different permutations and combinations to check any variation in the water collection dynamics would be another interesting study. The knowledge and the ndings based on these efficient fog-collecting surfaces at a large scale can pave way for the design and improvement of highly efficient surfaces to be utilized in fog-harvesting and other industrial applications.…”

“…15,21,[46][47][48] These forces can hinder the fog collection cycle from restarting and raise the risk of droplet re-evaporation, either by halting the timely removal of the nucleated and grown droplet or by prematurely removing the nucleated droplets. [49][50][51] Although the current bioinspired fog collectors are quite successful in producing a reasonable amount of water, the transport of water is still of vital importance to the removal of captured droplets. With respect to the disadvantages of gravity-driven bioinspired fog collectors at a large scale, droplet retention on the functional surfaces may suffer from severe re-evaporation under fog ow, which may have a major effect on the efficiency and the consistency of the fog collectors.…”