Counterion-mediated modulation of electroadhesion in polyanionic/polycationic hydrogels: mechanisms and performance

Reversible electroadhesive polyelectrolyte gels have emerged as promising materials for flexible electronic and soft robotic applications. While current research predominantly emphasizes polymer design and structural optimization to enhance both the reversibility and strength of electroadhesion, fundamental limitations persist in elucidating ion-mediated interfacial mechanisms. Herein, the synergistic effects of ion species selection and interfacial engineering were systematically investigated through the development of distinct polyelectrolyte hydrogel assemblies. By varying counterion types (anions and cations) and ion concentrations, the ion-mediated mechanism governing reversible adhesion between polyanionic and polycationic hydrogels was elucidated. Combined electrochemical impedance spectroscopy and molecular dynamics simulations revealed that interfacial electroadhesion primarily resulted from electrostatic interactions within the ionic double layers. Optimizing counterion diffusion rates through ion species selection can reduce the interfacial ionic resistance and increase the capacitance of the ionic double layer, thereby enhancing the electroadhesive performance. The results indicated that LiCl hydrogels are suitable for single-use high-adhesion patches due to the accelerated Li⁺/Cl^- migration, whereas NaCl hydrogels are ideal for reusable electroadhesive patches. This counterion-mediated modulation strategy provides a universal framework for designing adaptive hydrogel interfaces with tunable adhesion properties.