Stretchable and conductive physical eutectogel based on type IV deep eutectic solvent through cation-bridging

This study demonstrates the facile fabrication of stretchable and conductive eutectogels by directly dispersing poly(acrylic acid) (PAA) in type IV deep eutectic solvents (DESs). These DESs contain metal chloride hydrates like MgCl₂ or ZnCl₂ as hydrogen bond acceptors and glycerol or ethylene glycol as hydrogen bond donors. The eutectogel demonstrated liquid-like behavior, characterized by shear-thinning with a yield stress, while its gel-like behavior was identified by a storage modulus greater than the loss modulus. Additionally, the solid-like behavior was evidenced by the stress–strain curves. The rheological and mechanical properties of eutectogels were found to depend significantly on the component and composition of DESs, as well as the concentration of PAA. The polymer network formation in type IV DESs is attributed to the cation-bridge mechanism, where divalent metal ions act as cross-linking agents among PAA polymers. The cross-linking mechanism has been examined by the ionic conductivity and IR spectroscopy analyses of the eutectogel. Due to the synergistic cation-bridging and hydrogen bonding, the eutectogel can display exceptional stretchability (∼1500 %) and remarkable conductivity (7.69 mS/cm).