Cellulose-based Superhydrophobic Surface Decorated with Functional Groups Showing Distinct Wetting Abilities to Manipulate Water Harvesting

Inspired by the distinct functions of desert beetles with efficient droplet nucleation and lotus leaves with excellent droplet removal, an integrated method is presented for the design of a superhydrophobic surface decorated with hydrophilic groups that can efficiently nucleate and remove water droplets. We constructed a cellulose-based superhydrophobic surface containing numerous olefin terminal groups by solvent exchange and spray coating. This surface is different from most of the reported biomimicking water harvesting surfaces that rely on complicated lithography and micropatterning techniques requiring special instruments. The obtained superhydrophobic surface was further modified using various thiol compounds via a thiol-ene reaction to manipulate the water harvesting property. The modified surfaces containing hydrophobic groups (e.g., 1-octadecanethiol and 1H,1H,2H,2H-perfluorodecanethiol) or a strong hydrophilic group (e.g., 3-mercaptopropionic acid and 6-mercapto-1-hexanol) exhibited insufficient fog collecting abilities due to poor water droplet nucleation or strong water adhesion. By contrast, the modified surface decorated with moderately hydrophilic amino groups combines the advantages of biological surfaces with distinct wetting features (such as fog-harvesting beetles and water-repellent lotus leaves), resulting in accelerated water nucleation and less compromise of the water removal efficiency. Molecular dynamic simulations revealed that the efficient droplet nucleation is attributed to the hydrophilic amino groups whereas the rapid droplet removal is due to the maintained superhydrophobicity of the amino group-modified surface. This strategy of decorating a superhydrophobic surface with moderately hydrophilic functional groups provides insight into the manipulation of droplet nucleation and removal for water collection efficiency.