Moisture Absorbing and Water Self‐Releasing from Hybrid Hydrogel Desiccants

• Published in: Advanced functional materials 2024-05, Vol.34 (19), p.n/a
• Main Authors: Nah, So Hee, Lee, Yunchan, Yu, Kun‐Hao, Chi, Yinding, Lee, Hyemin, Chen, Baohong, Patel, Mohit, Wang, Kunyu, Yang, Shu
• Format: Article
• Language: English
• Subjects: Absorption; Atmospheric moisture; atmospheric water harvesting; Crosslinking; Desiccants; Diffusion rate; Droplets; Edge effect; Energy harvesting; Film thickness; Fresh water; Hydrogels; hydrophobic patterns; Hydrophobicity; Lithium chloride; Moisture absorption; Nucleation; Polyacrylic acid; Relative humidity; Releasing; Room temperature; salt‐embedded hydrogel desiccant; self‐releasing of water; Surface chemistry; Water drops
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202313881

Atmospheric moisture is a valuable resource for fresh water and potentially sustainable energy. However, direct harvesting water from moisture (the vapor form) remains the most challenging. Hybrid desiccants made from hydrogels embedded with salt offer promise in absorbing moisture. However, the desorption process often requires additional energy to heat the samples. Here, poly(acrylic acid) (PAA) hydrogels embedded with lithium chloride are prepared, demonstratng simultaneous moisture absorption and self‐release of liquid water at room temperature with 50–90% relative humidity. The water self‐releasing process can be separated into two distinct stages: 1) surface release, where water droplets grow on the hydrogel surface due to differences in nucleation and diffusion rates, and 2) bulk release, triggered by the collapse of polymer chains, subsequently releasing water from the hydrogel network. Factors such as salt concentration, hydrogel crosslinking density, and film thickness are investigated to better understand the moisture absorption and water‐releasing processes. Moreover, hydrophobic domains are introduced onto the salt‐embedded PAA films, creating an edge effect that enhances the droplet growth rates. When the hydrophobic domains are patterned, the movement of released water can be guided, resulting in a threefold increase in water removal rate attributed to gravitational force. Hybrid hydrogels from poly(acrylic acid) embedded with lithium chloride can simultaneously capture atmospheric water and release it in the liquid phase at room temperature with 50–90% relative humidity, attributed to limited diffusion of water into the hydrogel network and collapse of the polymer chains in bulk. Further, hydrophobic patterns on the hydrogel create the edge effect that expedites water removal.