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DOI: 10.1002/adma. 201502556 microstructured elastomer layer, achieving both mechanical flexibility and rapid sensing response in a millisecond range.[24] In our previous work, we have employed IL as capacitive sensing elements to resolve both normal and shear force/pressure, where an elastic capacitive interface between electrolyte and electrodes offers ultrahigh sensitivity (of 1.46 nF kPa− 1) and flexibility, in addition to the optical transparency and fast response.[28]

In this Communication, we have first demonstrated the utilization of an ionic gel matrix as a thin-film capacitive sensing material, referred to as iontronic film, for flexible and rapid responsive detections, eg, emerging wearable and health sensing applications. As a unique characteristic of the ionicelectronic contact, the interfacial capacitance lies on the formation of an electrical double layer (EDL), in which electrons on the electrode and the counter ions from the iontronic film accumulate and attract to each other at a nanoscopic distance, which leads to an ultrahigh unit-area capacitance.[7, 29] Utilizing the highly capacitive interface at the ionic-electronic contact, the iontronic film sensor offers the highest unit-area capacitance (of 5.4 µF cm− 2) among all solid-state capacitive sensors, leading to the ultrahigh mechanical-to-capacitive sensitivity of 3.1 nF kPa− 1, which is more than a thousand time greater than that of the traditional solid-state counterparts.[24, 30] In addition, our pressure sensor exhibits an excellent mechanical stability (less than 3% variation in the device sensitivity) while it is deformed on the surface with various radii of curvatures (50––200 mm). Moreover, the …