Hydrogen-bond disruption in molecularly engineered Janus evaporators for enhanced solar desalination

Hydrogels have emerged as effective evaporator platforms, significantly enhancing evaporation rates by disrupting water's hydrogen bond network. Here, we present an advanced strategy to improve hydrogel evaporation performance by tailoring alkyl hydrophobic groups within biparental polyelectrolyte-shell micelles grafted onto the polyvinyl alcohol (PVA) hydrogel surface. Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) quaternized with methyl iodide (MeI) or ethyl iodide (EtI) formed the biparental polyelectrolyte shell, while poly(benzyl methacrylate) (PBzMA) constituted the micelle core, creating BE-MeI and BE-EtI micelles, respectively. The molecularly engineered BE-MeI micelles exhibited an optimized configuration of quaternary amines linked to hydrophobic groups, achieving a synergistic balance between water attraction via electrostatic interactions and water repulsion via steric hindrance. This configuration effectively disrupted the water's hydrogen bond network, lowering the water evaporation enthalpy to 1434 J g^-1. The BE-MeI micelle-grafted PVA hydrogel achieved a record-breaking evaporation rate of 4.1 kg m^-2 h^-1 under 1 sun irradiation, surpassing prior benchmarks, including our previously reported poly(4-vinyl pyridine) quaternized by a MeI system. Additionally, the grafted micelle layer exhibited a salt rejection ratio of 99.62%, ensuring excellent desalination performance. The biparental polyelectrolyte-shell micelle grafting strategy is broadly applicable across diverse hydrogel systems, representing a significant advancement in solar-driven desalination technology.