Water-harvesting polymer coatings for plant leaves†

Abstract

Climate change-induced water scarcity threatens global plant life and agricultural productivity. Here, we present a novel atmospheric water harvesting (AWH) coating designed to alleviate heat and dry stress potentially. This polymer coating utilizes block copolymers carrying catechol-anchoring groups, specifically poly(dopamine methacrylamide) (PDOMA), to adhere to plant leaves. As a hydrophilic block, either poly((oligoethylene glycol) methacrylate) (POEGMA) or the thermoresponsive block poly(N-isopropylacrylamide) (PNIPAM) was used, which can adsorb water from the air during cooler periods in its hydrophilic state. As the temperature increases above the lower critical solution temperature (LCST) of PNIPAM, the polymer transitions to a hydrophobic state, releasing the captured water to the leaf surface. We synthesized PNIPAM-b-PDOMA copolymers via RAFT polymerization and confirmed their composition (IR, ¹H NMR and ¹H DOSY NMR spectroscopy) with a cloud point temperature of 33 ± 1 °C. The coatings were applied to model substrates (SiO₂, polyethylene) and corn leaves. Compared to uncoated controls, coated substrates demonstrated a substantial increase in water uptake from humid air, absorbing up to 50 wt% of the coating's weight. The coating's adherence and thermoresponsive behavior were confirmed on corn leaves through contact angle measurements, showing a shift from hydrophilic (29 ± 3°) below the LCST to hydrophobic (80 ± 2°) above the LCST, closer to the native, hydrophobic leaf (110 ± 10°). Crucially, photosynthesis induction experiments revealed that the coating did not negatively impact the plant's natural photosynthetic processes. This study establishes a promising copolymer platform for developing AWH coatings to support plants in the face of increasing drought conditions.