Block Copolymer‐Based Supramolecular Ionogels for Accurate On‐Skin Motion Monitoring

Abstract

Interest in wearable and stretchable on‐skin motion sensors has grown rapidly in recent years. To expand their applicability, the sensing element must accurately detect external stimuli; however, weak adhesiveness of the sensor to a target object has been a major challenge in developing such practical and versatile devices. In this study, freestanding, stretchable, and self‐adhesive ionogel conductors are demonstrated which are composed of an associating polymer network and ionic liquid that enable conformal contact between the sensor and skin even during dynamic movement. The network of ionogel is formed by noncovalent association of two diblock copolymers, where phase‐separated micellar clusters are interconnected via hydrogen bonds between corona blocks. The resulting ionogels exhibit superior adhesive characteristics, including a very high lift‐off force of 93.3 N m−1, as well as excellent elasticity (strain at break ≈720%), toughness (≈2479 kJ m−3), thermal stability (≈150 °C), and high ionic conductivity (≈17.8 mS cm−1 at 150 °C). These adhesive ionogels are successfully applied to stretchable on‐skin strain sensors as sensing elements. The resulting devices accurately monitor the movement of body parts such as the wrist, finger, ankle, and neck while maintaining intimate contact with the skin, which was not previously possible with conventional non‐adhesive ionogels.

Spatial Adjustment Strategy to Improve the Sensitivity of Ionogels for Flexible Sensors

“…Under the rapid exten-sion of 50% strain, the sensor B-IG-5 has a fast response speed and a short response time (160 ms), which was comparable to most ionogels strain sensors. [36,38,39] This indicates that the sensor can detect mechanical deformation without response delay (Figure 5c). The strain was repeated 1000 times with 50% strain, and the sensory stability of the B-IG-5 was further investigated.…”

“…Without any change in chemical composition and ratio of the ionogel compared to B-IG, the prepared sensor by B-IG-5 has the best sensitivity, whose GF is calculated as 1.9 at the strain of 100% (up to 1.6 times of B-IG), and it increased to 2.82 at the strain of 300%. Figure 4c shows the GF versus strain for stretchable ionogel sensors based on various polymer and IL, [36][37][38][39][40][41][42][43][44][45][46][47][48][49] the type of polymer and IL basically determine the level of sensitivity. The detailed information and properties of our ionogel in different strains are listed in Table S4 (Supporting Information).…”

Ultra-stretchable ion gels based on physically cross-linked polymer networks

“…Motion sensor based on P(EA-co-AA-co-AANa) ion gel When the gel deforms, its cross-sectional area, thickness, etc., will change, which will affect its ionic conductivity and further be reflected in the change in the resistance value. [34][35][36] By monitoring the change of the resistance value of the sample 78-10-12 during stretching, the relationship between the tensile strain and the resistance value can be obtained. Fig.…”

Stretchable solvent-free ionic conductor with self-wrinkling microstructures for ultrasensitive strain sensor

“…19 However, since utilizing ions as charge carriers, the fluid character of ionic media and the viscoelastic property of the flexible polymer network leads to poor strain modulation of ion conduction. 20,21 As a result, nearly all the ionic conductor-based strain sensors suffer from low sensitivity with a gauge factor (GF) smaller than 4 and serious signal hysteresis, [22][23][24][25] which seriously affect signal conversion and transmission in the sensor.…”