Accelerating water collection cycle by surface energy gradient of micro hole pattern on composite nanofiber membrane.

Atmospheric water harvesting provides a straightforward method to secure freshwater in arid environments without requiring energy consumption or infrastructure. The efficient water collection from moist air relies on the surface energy gradient by asymmetric material structures. The control of droplet nucleation, condensation, and shedding is crucial for enhancing water collection efficiency. The non-homogeneous surface with hydrophobic and hydrophilic characteristics promotes the nucleation of water droplets. Composite nanofiber membrane (CNM) with a porous surface is fabricated using dual electrospinning with poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP) and polyamide-6(PA6) materials. The laser-ablated micro holes on the membrane facilitate the growth of water droplets. Due to the decreased contact surface of the droplet, covering the hole patterns is unstable to develop into water film and easily rolls off the surface. This renewed surface with hole patterns initiates the fog harvesting cycle again. The wettability gradient of the through-plane in bilayered-CNM, combined with the hole pattern, accelerates the fog harvesting cycle. The hole-patterned bilayer structure improved the water collection rate from 0.145 mm3/s to 0.288 mm3/s on the CNM surface with a PVDF-HFP/PA6 ratio of 0.86/0.14. The integration of laser processing with dual electrospinning has the potential for continuous mass production of functional membranes in a single step. [Display omitted] • Nanofiber membrane with laser hole pattern structure is presented for fog harvesting. • Dual electrospinning is applied to fabricate composite nanofiber membrane (CNM). • Bilayer CNM induces a wettability gradient towards the depth direction of membrane. • Bilayer CNM with hole pattern promotes water droplet condensation-shedding cycle. [ABSTRACT FROM AUTHOR]