Multimodal Wearable Ionoskins Enabling Independent Recognition of External Stimuli Without Crosstalk.

Wearable ionoskins are one of the representative examples of the many useful applications offered by deformable stimuli-responsive sensory platforms. Herein, ionotronic thermo-mechano-multimodal response sensors are proposed, which can independently detect changes in temperature and mechanical stimuli without crosstalk. For this purpose, mechanically robust, thermo-responsive ion gels composed of poly(styrene-ran-n-butyl methacrylate) (PS-r-PnBMA, copolymer gelator) and 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMI][TFSI], ionic liquid) are prepared. The optical transmittance change arising from the lower critical solution temperature (LCST) phenomenon between PnBMA and [BMI][TFSI] is exploited to track the external temperature, creating a new concept of the temperature coefficient of transmittance (TCT). The TCT of this system (-11.5% °C-1 ) is observed to be more sensitive to temperature fluctuations than the conventional metric of temperature coefficient of resistance. The tailoring molecular characteristics of gelators selectively improved the mechanical robustness of the gel, providing an additional application opportunity for strain sensors. This functional sensory platform, which is attached to a robot finger, can successfully detect thermal and mechanical environmental changes through variations in the optical (transmittance) and electrical (resistance) properties of the ion gel, respectively, indicating the high practicality of on-skin multimodal wearable sensors.

Soft Template-Assisted Fabrication of Mesoporous Graphenes for High-Performance Energy Storage Systems.

Graphene is a promising active material for electric double layer supercapacitors (EDLCs) due to its high electric conductivity and lightweight nature. However, for practical uses as a power source of electronic devices, a porous structure is advantageous to maximize specific energy density. Here, we propose a facile fabrication approach of mesoporous graphene (m-G), in which self-assembled mesoporous structures of poly(styrene)-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) are exploited as both mesostructured catalytic template and a carbon source. Notably, the mesostructured catalytic template is sufficient to act as a rigid support without structural collapse, while PS-b-P2VP converts to graphene, generating m-G with a pore diameter of ca. 3.5 nm and high specific surface area of 186 m2/g. When the EDLCs were prepared using the obtained m-G and ionic liquids, excellent electrochemical behaviors were achieved even at high operation voltages (0 ∼ 3.5 V), including a large specific capacitance (130.2 F/g at 0.2 A/g), high-energy density of 55.4 W h/kg at power density of 350 W/kg, and excellent cycle stability (>10,000 cycles). This study demonstrates that m-G is a promising material for high-performance energy storage devices.

Binary Co-Gelator Strategy: Toward Highly Deformable Ionic Conductors for Wearable Ionoskins.

Stretchable ionic conductors have been actively developed due to the increasing demand for wearable electrochemical platforms. Herein, we propose a convenient and effective strategy for tailoring the mechanical deformability of ionic conductors. The mixing of poly(methyl methacrylate) (PMMA, polymer gelator) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMI][TFSI], ionic liquid) produces mechanically stiff ionic conductors. To reduce the chain entanglement of polymer gelators and induce effective dissipation of applied stresses, flexible poly(butyl acrylate) (PBA) with a low glass-transition temperature is additionally doped into the ionic conductor. An extremely stretchable (∼1500%) homogeneous ternary ionic conductor is obtained without a notable change in electrochemical characteristics, unless the content of PBA exceeds the macrophase separation limit of 3 wt %. In addition, the mechanical elasticity (1.8 × 105 Pa) and durability (e.g., recovery ratio of ∼86.3% after 1000 stretching/releasing cycles) of the conductor further support its suitability as a strain sensory platform. In contrast to conventional ionoskins that have to fit the area of target body parts, even a small piece of the ternary ionic conductor successfully monitors human motion over large areas by taking advantage of its superior deformability.

Ion-cluster-mediated ultrafast self-healable ionoconductors for reconfigurable electronics.

Implementing self-healing capabilities in a deformable platform is one of the critical challenges for achieving future wearable electronics with high durability and reliability. Conventional systems are mostly based on polymeric materials, so their self-healing usually proceeds at elevated temperatures to promote chain flexibility and reduce healing time. Here, we propose an ion-cluster-driven self-healable ionoconductor composed of rationally designed copolymers and ionic liquids. After complete cleavage, the ionoconductor can be repaired with high efficiency (∼90.3%) within 1 min even at 25 °C, which is mainly attributed to the dynamic formation of ion clusters between the charged moieties in copolymers and ionic liquids. By taking advantages of the superior self-healing performance, stretchability (∼1130%), non-volatility (over 6 months), and ability to be easily shaped as desired through cutting and re-assembly protocol, reconfigurable, deformable light-emitting electroluminescent displays are successfully demonstrated as promising electronic platforms for future applications.

Porous Ion Gel: A Versatile Ionotronic Sensory Platform for High-Performance, Wearable Ionoskins with Electrical and Optical Dual Output.

The development of elastic ionic conductors offers opportunities to fabricate key wearable ionic components such as ionoskins that can perceive mechanical deformation. However, there is still plenty of room to overcome the trade-off between sensitivity and detectable range of previous systems and impart additional functionality. Here, we propose porous ion gels for high-performance, functional ionic sensory platforms. The porous ion gels can be effectively deformed by closing pores even with a small pressure, and a large change in the contact area of the gel and the electrode is induced, leading to a significant difference in electrical double-layer capacitance. The porous ion gels are applied to ionoskins after optimizing mechanical characteristics by adjusting gel parameters. The device indicates a high sensitivity of ∼152.8 kPa-1, a broad sensory pressure range (up to 400 kPa), and excellent durability (>6000 cycles). Successful monitoring of various human motions that induce different magnitudes of pressure is demonstrated with high precision. More interestingly, the functionality of the porous ion gel is extended to include electrochemiluminescence (ECL), resulting in the production of emissive ECL ionoskins. The ECL intensity from the emissive ionoskin is linearly correlated with the applied pressure, which can even be inferred even by the naked eye. The porous ion gel-based functional ionoskins are expected to be key components in future sensory ionotronics.