Conductive Organohydrogels with Ultrastretchability, Antifreezing, Self-Healing, and Adhesive Properties for Motion Detection and Signal Transmission

Abstract

Conductive hydrogels had demonstrated significant prospect in the field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature falls below zero. Here, a novel conductive organohydrogel was developed by introducing polyelectrolytes and glycerol into hydrogels. The gel exhibited excellent elongation, self-healing, and self-adhesive performance for various materials. Moreover, the gel could withstand a low temperature of −20 °C for 24 h without freezing and still maintain good conductivity and self-healing properties. As a result, the sample could be applied for motion detection and signal transmission. For example, it can respond to finger movements and transmit network signals like network cables. Therefore, it was envisioned that the effective design strategy for conductive organohydrogels with antifreezing, toughness, self-healing, and self-adhesive properties would provide wide applications of flexible wearable devices.

Water‐Processable, Stretchable, Self‐Healable, Thermally Stable, and Transparent Ionic Conductors for Actuators and Sensors

“…In good‐poor solvent theory, hydrophobic polymer shrinks more in aqueous system, leading to stronger polymer–polymer interaction than polymer–solvent interaction (Figure c) . Furthermore, in order to prevent stiffening arising from water evaporation from hydrogel, dilute aqueous solvent with glycerol (GY), which has high boiling point (290 °C), nontoxic, low‐cost and high compatibility with the ionic chain was used . The glycerol can play a role of a plasticizer without evaporation, maintaining its presence in the gels.…”

Cellulose Nanofibrils Enhanced, Strong, Stretchable, Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

“…High ionic conductivity has only been observed for ICHs with weak mechanical properties, such as polyacrylamide‐based hydrogel (stress (σ 1 ) = 22 kPa, conductivity (σ 2 ) = 2.9 S m −1 ), [ 10d ] polyacrylamide‐polyvinylpyrrolidone double‐network hydrogel (σ 1 = 6 kPa, σ 2 = 2 S m −1 ), [10b] polyvinyl alcohol (PVA)/H 2 O/ethylene glycol organohydrogel (σ 1 = 100 kPa, σ 2 = 1.5 S m −1 ), [ 11 ] and polymethacrylate organohydrogel (σ 1 = 5 kPa, σ 2 = 1.5 S m −1 ). [ 12 ] On another hand, strong hydrogel generally has low ionic conductivity due to the restricted ion mobility within the tight hydrogel network structures. [ 13 ] Hence, it remains a grand challenge to balance the performance of high strength, high toughness, as well as high ionic conductivity.…”

“…Incorporating cryoprotectant into hydrogel can suppress ice crystal formation as well as increase the crosslink density, leading to a stronger organohydrogel. [ 11,12,13b ] However, ionic conductivity will decrease due to the reduced ion dissociation in organic solvent as well as ion mobility with enhanced crosslinking density. The ionic conductivity of ethylene glycol and glycerol based anti‐freezing organohydrogels has been reported to be around 0.035–0.765 S m −1 , [ 13a,18b,21 ] which will further reduce to 0.02 S m −1 at sub‐zero temperature.…”

Strategies for Designing Stretchable Strain Sensors and Conductors

“…At sub‐zero temperatures, the water in hydrogels inevitably freeze and lose conductivity. To overcome this problem, antifreezing conductive organohydrogels have been developed . Rong et al used H 2 O/ethylene glycol binary solvent to replace pure water in the common hydrogels.…”

“…Thanks to the high freezing tolerance, the organohydrogels exhibited stable flexibility and strain sensitivity even at −40 °C. Similar water‐organic solvent mixtures such as dimethyl sulfoxide, glycerol, or oil with water can greatly reduce the freezing point, which can be utilized to prevent the hydrogels from being frozen at low temperature …”