Ligand-Controlled Coordination in Metal-Salt Deep Eutectic Solvents for Regulating Phase Behavior, Network Connectivity, and Mechanical Performance of Stretchable Eutectogels

DES-based eutectogels suffer from limited mechanical performance due to solvent-induced plasticization, and phase separation alone cannot reliably reinforce network structures. Although metal-salt-based DESs enable coordination reinforcement, how ligand identity regulates coordination environment, phase behavior, and interdomain connectivity remains unclear. Here, we show that ligand-controlled coordination dictates both network formation and phase behavior in intrinsically phase-separating eutectogels. Using poly(N-isopropylacrylamide) (PNIPA) and ZnCl 2 -based DESs with acetamide (AcAm) and ethylene glycol (EG) as ligands of distinct coordination strength, two regimes are identified. In PNIPA/ZnCl 2 –AcAm, weak Zn 2+ –AcAm coordination enables Zn 2+ bridging between polymer chains, suppressing phase separation and forming a homogeneous network with uniform polymer–Zn 2+ interactions, high transparency (> 90%), high elongation (2553%), and tensile strength of 5.21 MPa. In contrast, PNIPA/ZnCl 2 –EG shows strong Zn 2+ –EG coordination, limiting polymer–metal interactions and inducing coordination-stabilized phase-separated domains with reduced transparency (~50%), higher strength (14.45 MPa), and limited elongation (85%). Non-coordinating choline chloride DESs yield weak networks (< 1.3 MPa), confirming that coordination-governed connectivity dominates reinforcement. A mixed-ligand system ([AcAm]/[EG] = 1:2) achieves balanced strength (7.67 MPa) and elongation (1270%). These results establish ligand-controlled coordination as a general strategy to regulate phase separation and interdomain connectivity, enabling simultaneous optimization of strength and stretchability. Graphical Ligand-controlled coordination in metal-salt deep eutectic solvents regulates the competition between polymer–metal and ligand–metal interactions in eutectogels. This coordination balance governs phase separation behavior and interdomain connectivity, leading to either homogeneous or phase-separated networks with distinct mechanical responses. A mixed-ligand strategy enables simultaneous enhancement of strength and stretchability.