Biomimetic Janus Membranes Fabricated via Single-Step Electrospinning: Bead-on-String Architecture for Enhanced Atmospheric Fog Harvesting.

To address water scarcity in arid regions, this study proposes a high-efficiency fog harvesting material development strategy based on wettability gradient regulation. Controllable assembly of polyvinyl chloride nanofibers with bead-on-string structures on hydrophilic substrate surfaces is achieved through a 5 min electrospinning process. The fabricated Janus membrane achieves a contact angle differential of 141°, establishing an asymmetric wetting structure that enables directional droplet transport. Experimental data show that its fog water collection flux is 2.1 times higher than those of traditional hydrophilic materials. Surface water droplets were absorbed by the Janus membrane in only 2 ms, while they were absorbed by the hydrophilic membrane in at least 5 ms. Moreover, after the water droplets were absorbed, the Janus membrane surface can remain in a fresh, dry state, which is conducive to further water absorption. The underlying mechanisms for the enhanced fog harvesting performance were detailed, with numerical simulations used to study the impact of the hydrophilic layer's wettability on liquid penetration. Such a Janus membrane can be a promising candidate for fog harvesting against the water crisis.