Transparent Flexible Moisture-Absorbing Film as Ca2+ Pump Dispenser Mimic

Salt-containing moisture-absorbing materials play an important role in atmospheric water harvesting, humidity management, and water retention, but salt loss due to the water solubility of salt hinders their moisture-absorbing capacity. Herein, a smart transparent flexible film as a Ca2+ pump dispenser mimic was developed by cross-linking sodium alginate (SA) and sodium polyacrylate (PAAS) with CaCl2 for outstanding salt fixation and sustainable self-driven moisture absorption. The film can fix more Ca2+ and control the Ca2+ ratio on the surface and interior of the film by adjusting the SA/PAAS ratio to realize Ca2+ storage and controllable distribution, thus reducing surface Ca2+ loss during water rinsing. By tracing the migration path of Ca2+ after water rinsing, it is found that Ca2+ inside the film can be automatically pumped to the surface, realizing the replenishment and redistribution of Ca2+ to ensure moisture-absorbing capacity. The film exhibits high water content (109.9%) at 30 degrees C and 80% RH. After rinsing, the recovered moisture-absorbing capacity of the film still meets the requirements of spectral simulation of plant leaves (spectral correlation coefficient r(m) similar to 0.987), demonstrating the sustainability of the film in the spectral simulation field. The film provides insights into the stable hygroscopic ability in multiclimate and multiscene conditions.