Molecular Simulation-Guided Design of H-Bonding-Reinforced Trihydroxy-Phenolics/Poly(vinyl alcohol) Composite Hydrogel.

Small-molecule blending is an effective strategy for improving the mechanical properties of poly(vinyl alcohol) (PVA). However, the influence of structural differences among phenolics on the toughening mechanism remains unclear. In this study, we systematically investigated the reinforcing effects of three trihydroxy-phenolics (apigenin, galangin, and baicalein) on PVA hydrogels by combining molecular simulations with experimental validation. Molecular simulations predicted that H-bonding crosslinking between phenolics and PVA chains is the central reinforcement mechanism, and that the spatial arrangement of hydroxyl groups and the competition between intermolecular H-bonding ultimately determine the performance. Structural characterization and experimental validation showed that apigenin, owing to the dispersed spatial distribution of its three hydroxyl groups, exhibits stronger H-bonding crosslinking ability and achieves the most significant reinforcement. After a single freeze-thaw cycle, all trihydroxy-phenolics/PVA composite hydrogels exhibited markedly better mechanical properties than pure PVA hydrogels, with the following strength order: apigenin/PVA > galangin/PVA ≈ baicalein/PVA. This study provides a rapid and efficient theoretical model and a reference case for small-molecule toughened PVA hydrogels.