Much effort has recently been put towards a means of freshwater water collection that is available in even the most arid climates: fog and dew harvesting. Novel bio-mimetic approaches to improve the traditional fog collector have focused on emulating plants and insects that are endemic to arid regions, yet are able to collect enough atmospheric water to survive. Hydrophilic/hydrophobic micropatterns observed on the Namib desert beetle (Stenocara) could increase the efficiency of water collection by allowing water to coalesce on the hydrophilic patches and then easily flow away on the hydrophobic areas. The ability to directly add confined spots of a hydrophilic or “sticky” hydrophobic material to a superhydrophobic surface in order to create wetting contrast has remained a challenge because aqueous solutions of a hydrophilic polymer are unable to adhere to a superhydrophobic surface, while solutions of hydrophobic polymers in organic solvents easily wet a superhydrophobic surface, increasing the spot size and reducing control of spot location.
We present surfaces with high wetting contrast through the direct dispensing and curing of mixtures of polydimethylsiloxane (PDMS) and toluene onto superomniphobic surfaces of fibrous perfluoralkyl methacrylic copolymer (PMC) and fumed silica nanoparticles. As electrospun, PMC/silica nanofiber mats showed high contact angles for both water and oil. However, fibers were observed to peel away with passing droplets. After heating the fibers, the fibers did not peel away anymore when in contact with liquids, forming instead a stable superomniphobic surface. PDMS/toluene droplets could easily be placed on the substrate using an ordinary syringe and needle assembly without wetting it. The fog harvesting ability of surfaces composed of varying wetting patterns was then investigated. Spot size and separation were both found to have a significant effect on the rate and initial time of fog collection, as well as on the mechanism of droplet accumulation and removal.