The polymer gel is composed of polymeric chains which are crosslinked in a three-dimensional (3D) network structure and liquid which is widely applied to tissue engineering, medical treatment, and solid state electrochemical devices. The gel contains a large amount of water inside the three-dimensional network structure. The human body is also mostly composed of water, hence, the percentage of water in human body is relatively high similar to hydrogel. However, water contained in the gel evaporates in the air atmosphere.

Among various kind of gel, ion gel possessing ionic liquid is beneficial for applications since ionic liquids are liquid salts at room temperature and have useful properties such as non-volatility, non-inflammability, electrochemical stability, thermal stability and high ionic conductivity. In this study, we investigated the piezoelectric properties of ion gels to apply them for touch and pressure sensors in soft-matter robotics.

In this study, the used ion gel was made utilizing thiol-ene reaction and was composed of thiol monomer. The thiol-ene reaction is hardly influenced by the surrounding environment, hence, we can easily make ion gel. In addition, it is possible to form any objects using a photopolymerization initiator and a 3D printer. The aim of this research is to develop a tactile sensor using ion gel having non-volatility, non-flammability, thermal stability, high conductivity and softness close to humans.

The sensor is composed of ion gel and silicone rubber. It was made by injecting an ion gel into silicone rubber. The changes of impedance is measured by the change of shape of the ion gel due to the pressure. The sensor was tested with a press tester and an LCR meter for pressure sensing. It shows 521 kPa in maximum pressure sensing.

Currently, we are working on three-dimensional modeling of the sensor by using an ion gel and an insulating gel instead of using a mold. The technique shown in this study is expected to be applied to soft robot and robot hand.