Dynamic Water Microskin Induced by Photothermally Responsive Interpenetrating Hydrogel Networks for High-Performance Light-Tracking Water Evaporation

Solar-driven interfacial water evaporation is attracting increasing attention as a promising environmentally-friendly solution to freshwater scarcity. It has been proven that a thin water layer on photothermal materials can prevent solar energy from invalidly heating the excess water to enhance the evaporation rate. However, the current water layers are usually formed on inelastic materials via confined capillarity, which are static and uncontrollable. Herein, we propose a flexible hydrogel-based photothermal conversion material with thermal responsiveness by facile frontal polymerization, which can generate a unique dynamic water microskin (DWMS) during the solar evaporation process. The copolymerized hydrogel, introduced by the second polymeric poly(vinyl alcohol) network and thermally responsive poly(N-isopropylacrylamide) (PNIPAM), exhibits reinforced mechanical strength and photothermally triggers reversible shrinking/swelling cycles that enable a thin water layer (≈32 µm) to balance the feedwater supply and photothermic energy input dynamically. As a result, a stable superior vaporization rate of 8.7 kg m⁻² h⁻¹ is achieved based on a cylindrical hydrogel with 6 cm height under 1 sun. Moreover, the simultaneous responsive bending allows efficient omnidirectional solar evaporation by light-tracking to ensure maximum perpendicular solar absorption, which provides an alternative strategy for durable high-efficiency solar evaporators for effective thermal management and solar utilization.