Wettability Contrast in the Hexagonally Patterned Gold Substrate of Distinct Morphologies for Enhanced Fog Harvesting

Abstract

Inspired by the Stenocara beetle’s hydrophobic–hydrophilic surface, we fabricated hexagonally patterned hydrophobic–hydrophilic surfaces consisting of silicon and gold regions using colloidal lithography and selective surface functionalization. We investigated surface wettability for different patterns (hexagonally ordered nanotriangles and nanoholes) and the influence of surface functionalization (octadecanethiol and 16-mercaptohexadecanoic acid/octadecyltrichlorosilane (MHA/OTS)). The as-prepared patterned substrates exhibit hydrophilicity, which transforms to hydrophobicity after surface functionalization. The MHA/OTS functionalization results in maximum enhancement in the contact angle (114 ± 0.4°) with the least contact angle hysteresis (19 ± 2°). Fog harvesting studies show that the patterned substrate has a higher water collection rate, a factor of 1.32, than the nonpatterned substrates. A further enhancement in water collection (almost twice) is observed with selective functionalization. The patterned (nanohole) and functionalized (MHA/OTS) substrate facilitates rapid falling of droplets at a frequency of 20 mHz and an average droplet mass of 15 ± 2 mg/cm2. Furthermore, it yielded a maximum water collection rate of 1051 ± 132 mg cm–2 h–1. This work provides valuable insights into the influence of surface wettability and morphology for fog harvesting applications.

Fog Harvesting with Highly Wetting and Nonwetting Vertical Strips

“…There is currently no clear consensus as to which type of surface, superhydrophobic − or superhydrophilic, , is more efficient in fog harvesting. This conundrum is underscored by findings showing that hybrid architectures, which have juxtaposed superhydrophobic and superhydrophilic regions, can offer more efficient routes for enhanced water harvesting capacity. − However, these structures tend to have complicated designs, making it difficult to elucidate the underlying mechanisms contributing to the improved performance.…”

Bioinspired Asymmetric Surface Property of Functionalized Mesh to Maximize the Efficiency of Fog Harvesting

“…It has been established that the mechanism of fog harvesting involves three crucial steps, namely active nucleation, growth, and transportation [20] . The first two steps depend on the nucleation sites and surface wettability to a large extent, which are determined by the surface morphology and surface energy [21] . Hydrophilic surfaces promote higher nucleation due to higher surface energy, but they do not allow the water droplet to fall from the surface due to higher adhesion [21] .…”

“…The first two steps depend on the nucleation sites and surface wettability to a large extent, which are determined by the surface morphology and surface energy [21] . Hydrophilic surfaces promote higher nucleation due to higher surface energy, but they do not allow the water droplet to fall from the surface due to higher adhesion [21] . On the other hand, hydrophobic surfaces exhibit low surface energy, accelerating the falling of water droplets from the surface but hindering nucleation [21] .…”

“…Hydrophilic surfaces promote higher nucleation due to higher surface energy, but they do not allow the water droplet to fall from the surface due to higher adhesion [21] . On the other hand, hydrophobic surfaces exhibit low surface energy, accelerating the falling of water droplets from the surface but hindering nucleation [21] . The hydrophilic surface also promotes a higher coalescence rate than hydrophobic surfaces [21] .…”

“…On the other hand, hydrophobic surfaces exhibit low surface energy, accelerating the falling of water droplets from the surface but hindering nucleation [21] . The hydrophilic surface also promotes a higher coalescence rate than hydrophobic surfaces [21] . Additionally, recent studies showed that a hydrophilic slippery rough surface with microgrooves and liquid‐infused nanotextures constructed on silicon wafers showed fast fog harvesting [22] .…”