Intrinsic Water Transport in Moisture-Capturing Hydrogels

Abstract

Moisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel− salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.

Chemistries and materials for atmospheric water harvesting

“…Typically, three transport resistances are identified within polymer sorbents: (i) the diffusion resistance of vapour from the external surface to the internal surface ( R ex–in ), (ii) the phase transition resistance in the liquefaction process ( R phas ), and (iii) the liquid transport resistance linked with the internal permeation of captured water ( R perm ). 56,57 R phas is often considered a minor component due to the strong hygroscopic nature of these polymers. The rate-limiting steps are usually R ex–in and R perm , influenced by structural features like surface area and porosity.…”