A Waterproof Ion‐Conducting Fluorinated Elastomer with 6000% Stretchability, Superior Ionic Conductivity, and Harsh Environment Tolerance

Abstract

The development of ionic conductors with extreme stretchability, superior ionic conductivity, and harsh‐environment resistance is urgent while challenging because the tailoring of these performances is mutually exclusive. Herein, a hydrophobicity‐constrained association strategy is presented for fabricating a liquid‐free ion‐conducting fluorinated elastomer (ICFE) with microphase‐separated structures. Hydrophilic nanodomains with long‐range ordering and selectively enriched Li ions provided high‐efficient conductive pathways, yielding impressive room‐temperature ionic conductivity of 3.5 × 10–3 S m–1. Hydrophobic nanodomains with abundant and reversible hydrogen bonds endow the ICFE with superior damage‐tolerant performances including ultrastretchability (>6000%), large toughness (17.1 MJ m–3) with notch insensitivity, antifatigue ability, and high‐efficiency self‐healability. Due to its liquid‐free characteristic and surface‐enriched hydrophobic nanodomains, the ICFE demonstrates an extreme temperature tolerance (−20 to 300 °C) and unique underwater resistance. The resultant ICFE is assembled into a proof‐of‐concept skin‐inspired sensor, showing impressive capacitive sensing performance with high sensitivity and wide‐strain‐range linearity (gauge factor to 1.0 in a strain range of 0–350%), excellent durability (>1000 cycles), and unique waterproofness in monitoring of complex human motions. It is believed that the hydrophobicity‐constrained association method boosts the fabrication of stretchable ionic conductors holding a great promise in skin‐inspired ionotronics with harsh‐environment tolerance.

Versatile Copolymer for Stretchable and Self-healable Liquid-free Ionic Conductive Elastomers

“…Polymerizable deep eutectic ionic monomers, typically the complexation of acrylic acid and choline chloride, is one of the choices for synthesizing liquid-free ICEs with high ionic conductivity. , However, both the polymer matrix and solid salt are hygroscopic, which would cause some stability issues in electrical and mechanical performance under practical use. Incorporation of lithium salts into elastomer matrices is another promising approach for preparing liquid-free ICEs with stretchability and good conductivity where the polymer matrices are hydrophobic so that the influence of moisture can be minimized to help the devices’ environmental stability. , On the other hand, introducing ether oxygen segments such as polyethylene oxide blocks into the polymer matrix can effectively improve the ionic conductivity of ICEs since such segments can substantially dissociate Li salts and thus facilitate ion mobility together with the flexible segments. ,, However, the ICEs composited with salt lack structural integrity and may suffer from salt loss when encountering solvents.…”

Materials development in stretchable iontronics

“…In another study, by introducing microphase-separated structures, Zhang et al reported highly conductive ionic elastomers. 116 Their copolymers were composed of 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) and OEGMEA, where the Li ions favour the hydrophilic OEGMEA phase, while the TFSI anions favour the hydrophobic fluorinated HFBA phase. The selectively enriched Li + domain gave high ionic conductivity to the elastomers.…”

Flexible and adhesive liquid-free ionic conductive elastomers toward human–machine interaction

“…More recently, ionic conductive elastomers (ICE) have been developed, which consist of polymer networks and mobile ions, but contain no liquid. [27][28][29][30][31][32][33][34] Because they are liquid-free, ICE have no weight or performance loss in air, thus achieving durability and performance stability that are extremely difficult or even impossible to realize by hydrogels and ionic liquid gels. Such advantages enable ICE to be demonstrated for making flexible and stable transistors, 35 sensors, 36 electroluminescent devices, 37 and triboelectric nanogenerators (TENGs).…”