Wireless Electrochemical Gel Actuators

Abstract

Soft actuators generate motion in response to external stimuli and are indispensable for soft robots, particularly future miniature robots with complex structure and motion. Similarly to conventional hard robots, electricity is suitable for the stimulation. However, previous electrochemical soft actuators require a tethered connection to a power supply, limiting their size, structure, and motion. Here, wireless electrochemical soft actuators composed of hydrogels and driven by bipolar electrochemistry are reported. Viologen, which dimerizes by one‐electron reduction and dissociates by one‐electron oxidation, is incorporated in the side chains of the gel networks and works as a reversible cross‐link. Wireless and reversible electrochemical actuation of the hydrogels, i.e., muscle‐like shrinking and swelling, is demonstrated at microscopic and even macroscopic scales.

Crystal structures and stimuli-responsive properties for three novel D–A type salicylhydrazide–viologen compounds with free radical properties under ambient conditions

“…In the previous study, the radical of viologen is always generated by physical methods, such as photoradiation. 8–12 Although compounds 1–3 have shown EPR signals that are related to the radicals at ambient temperature, it is supposed that the content of radicals might be lower than the stoichiometric amount. So, the photocurrent study was conducted herein.…”

“…Viologen as a stimuli-reactive material can undergo reversible redox processes in response to external stimuli, accompanied by the generation and quenching of viologen radicals. 1–7 The radical properties of viologen make it rich in properties, such as photochromic properties, 8–12 pressure-chromic properties, 13 thermochromic properties, 14 hydrochromic properties, 15 photocurrent effects, 16 ammonia-chromic properties, 17 etc. Usually, the applied conditions that promote this redox process are often harsh, such as high energy light sources, 8–12 strong pressure, 13 high temperatures, 14 etc.…”

“…1–7 The radical properties of viologen make it rich in properties, such as photochromic properties, 8–12 pressure-chromic properties, 13 thermochromic properties, 14 hydrochromic properties, 15 photocurrent effects, 16 ammonia-chromic properties, 17 etc. Usually, the applied conditions that promote this redox process are often harsh, such as high energy light sources, 8–12 strong pressure, 13 high temperatures, 14 etc. In general, the radical state of viologen is susceptible to quenching, which poses a challenge for the study of the radical properties of viologen.…”

Unconventional approaches for chiral resolution

“…In the presence of electroactive species, redox reactions take place only when the ΔV exceeds the correspondent thermodynamic threshold potential ( ΔV min ). Thus, it is possible to use this asymmetric reactivity to selectively couple a reaction of interest on one extremity of the BPE with an electrochemical process at the opposite end, acting as a transducer [ 60 – 62 ]. With this philosophy, BE has become an interesting tool for chiral recognition, particularly for the transduction of chirality across different length scales, from the molecular to the macroscopic level [ 63 ].…”