Water Flux Evaluation by Using Semipermeable Membrane and Various Poly(N‐Isopropyl Acrylamide) Hydrogels With Semi‐Interpenetrating Polymer Network

To combat global water scarcity, a novel atmospheric water harvesting (AWH) system is proposed that integrates deliquescent salts, a semipermeable membrane, and thermoresponsive hydrogels. Moisture is first absorbed by salts like CaCl 2 , then purified through a membrane using poly(N‐isopropylacrylamide) (PNIPAm)‐based hydrogels. Various PNIPAm hydrogels were developed with differing crosslinking densities, ionic charges, and hydrophilicities, including semi‐interpenetrating polymer networks (semi‐IPNs) containing PEG, amylopectin, or sepiolite. Water flux (W.F.) was assessed under different salt concentrations to evaluate the effects of hydrogel structure. Semi‐PEG11000 and semi‐IPNs with 20% amylopectin achieved high W.F. values (9.8 ± 1.0 and 19.0 ± 0.3 mL/m 2 h −1 ), indicating that large mole numbers and branched structures promote osmotic‐driven water transport. Freeze‐dried chitosan cryogels showed the highest W.F. (52.9 ± 10.6 mL/m 2 h −1 ), nearly five times greater than traditional semi‐IPNs, highlighting the benefit of porous macrostructures. A positive correlation between storage modulus and W.F. was observed; however, molecular features also influenced performance. These results emphasize the need to optimize both mechanical and molecular properties of hydrogels. Future development will aim to enhance thermo‐responsivity and water recovery efficiency, advancing practical AWH applications for atmospheric desalination.