Adaptive Deformation of Ionic Domains in Hydrogel Enforcing Dielectric Coupling for Sensitive Response to Mechanical Stretching

Abstract

Understanding the role of ionic migration in salt‐doped hydrogels is crucial for designing and using ionic skins. This study systematically investigates a typical ionic skin in the aspects of variations in capacitance and conductance with respect to stretch ratio. The ionic skin exhibits a sensitive response to the stretch ratio and input frequency. The capacitance can increase by 145% with increasing stretch ratio, whereas the ratio of capacitance variation to stretch ratio can exceed ≈0.25. The capacitance decreases with increasing frequency, whereas conductance increases. Capacitance or conductance with respect to stretch ratio exhibits an inflection point when the input frequency is fixed. Herein, an ionic domain model is proposed in which the ionic domains deform adaptively with global strain and released active ions. A portion of movable ions strengthens dielectric coupling, thereby significantly enhancing capacitance, and some of them act as free ion channels to increase conductance. The dielectric coupling is weakened when the active ions arriving at the electrode are depleted by either a significantly high frequency or large strain. This study will be useful for signal handling in ionic skin with high flux and high sensitivity and may also assist in understanding computing and memory principles of biological bodies.

Remarkable interfacial dielectric relaxation of physically cross-linked ice-hydrogelRemarkable interfacial dielectric relaxation of physically cross-linked ice-hydrogel

“…Given that hydrogels are mainly utilized in environments of relatively slow requests, the low-and mediate-frequency dielectric relaxation spectroscopy (DRS) could be a favored technique for probing the dynamic behavior of these polar units in the interfacial layer. In fact, DRS has been extensively utilized to characterize the electric responses of hydrogels, although the interfacial layer as a topic of DRS studies has been rarely touched [29][30][31][32] . This situation is more or less due to intrinsic difficulty in the characterization itself and the structural complexity of hydrogels.…”