Non-Power Multifunctional Flexible Sensors Based on Piezoionic Effect

With the rapid development of the Internet of Things (IoT) and artificial intelligence, wearable electronics have attracted considerable attention, where soft and flexible sensors are key devices. In this study, fabrication and characterization of non-power multifunctional flexible sensors driven by piezoionic effect have been presented. The ionic liquid-polyurethane (IL-PU) gels were prepared by casting the solution of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) and thermoplastic polyurethane. Then poly(3, 4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) containing ethylene glycol as flexible electrodes were deposited on both sides of the IL-PU gel by spin coating 1-2).<br/><br/>The sensing performance of the flexible sensor was evaluated by measuring electric charge and voltage under bending deformation. It was found that the flexible sensor generated positive and negative electric charges under bending and recovery processes, respectively, where the electric charge increased with increasing the velocity of bending. Moreover, the flexible sensor generated voltage on the order of mV upon bending, where the voltage was in proportion to the bending displacement. Thus, the IL-PU gel worked as a non-power multifunctional sensor responding to both velocity and displacement of bending. The mechanism can be explained in terms of the “piezoionic effect” due to the difference of ionic mobility between EMI cations and TFSI anions in the PU matrix, which was different from the conventional piezoelectric effect. On the basis of this phenomenon, we have succeeded in fabricating a wearable device using the non-power multifunctional flexible sensor suitable for the motion sensors in a wide field of IoT application.<br/><br/>1) H. Okuzaki, S. Takagi, F. Hishiki, R. Tanigawa, Sens. Actuators B, 194, 59 (2014).<br/>2) Y. Li, R. Tanigawa, H. Okuzaki, Smart Mater. Struct., 23, 074010 (2014).