Poly(l‑lactic acid) Janus Shape Memory\nMembranes with Uniform Vertically Penetrative Channels and Slit Pores\nfor Enhanced Fog Collection: Synergistic Effect of Transport through\nMembranes and Sequential Sliding Behaviors of Water Droplets

In\nthis work, poly(l-lactic acid) (PLLA) Janus shape memory\nmembranes with uniform vertically penetrative channels (SMEUVs) with\nslit pores have been fabricated with the help of template-assisting\nspray-coating and uniaxial tension at high temperature. During fog\ncollection, superhydrophobic and hydrophilic surfaces act as the front\n(fog-facing) side and back side, respectively, in which the structural\ncharacteristics play essential roles. On one hand, the vertically\npenetrative channels in SMEUVs and the special pore geometry contribute\nto lower resistance, accelerating the transport of captured water\nthrough membranes (from the superhydrophobic side to the hydrophilic\nside). On the other hand, the movement of water droplets along the\nback side has been guided by the oriented structures of slit pores,\npromoting the detachment of droplets from the hydrophilic surface.\nTheir synergistic effect removes captured water in a timely manner\nand provides fresh sites for the subsequent nucleation of water, enhancing\nfog collection performance. As a result, the optimal specimen (Janus\nSMEUVs with a draw ratio of 2.5, placed in the parallel direction)\nexhibits a much higher water collection rate (∼6×) relative\nto references (superhydrophobic and hydrophilic membranes). Our results\nare significant for sustainable development in view of both fog collection\nin arid regions and the biodegradability of PLLA.