Aromatic Residues Drive Polyelectrolyte Coacervates into Hydrogels for Underwater and Underoil Adhesion

Liquid–liquid phase separation (LLPS) of intrinsically disordered proteins (IDPs), followed by a liquid–solid transition, plays a crucial role in wet adhesion in natural systems. Although the mechanisms underlying these phase transitions are not fully understood, the presence of evenly distributed cationic and aromatic groups in IDPs is believed to facilitate the process. Inspired by this molecular feature, we designed a hydrophobic polyelectrolyte (Pcπ) with statistically distributed cationic and aromatic residues. Pcπ undergoes LLPS through complexation with phytic acid (PA), followed by a spontaneous transition into gel-like films in aqueous media. These Pcπ–PA films exhibit robust adhesion both underwater and under oil, outperforming conventional coacervate-based adhesives. In contrast, a corresponding polyelectrolyte in which the aromatic residues were substituted with methyl groups forms only liquid-like coacervates. This study highlights the critical role of aromatic residues in LLPS and phase transitions, offering valuable insights into developing protein-inspired adhesives capable of functioning in complex environments.