We report a new class of simple microfluidic strain sensors with high stretchability, transparency, sensitivity, and long-term stability with no considerable hysteresis and a fast response to various deformations by combining the merits of microfluidic techniques and ionic liquids. The high optical transparency of the strain sensors was achieved by introducing refractive-index matched ionic liquids into microfluidic networks or channels embedded in an elastomeric matrix. The microfluidic strain sensors offer the outstanding sensor performance under a variety of deformations induced by stretching, bending, pressing, and twisting of the microfluidic strain sensors. The principle of our microfluidic strain sensor is explained by a theoretical model based on the elastic channel deformation. In order to demonstrate its capability of practical usage, the simple-structured microfluidic strain sensors were performed onto a finger, wrist, and arm. The highly stretchable and transparent microfluidic strain sensors were successfully applied as potential platforms for distinctively monitoring a wide range of human body motions in real time. Our novel microfluidic strain sensors show great promise for making future stretchable electronic devices.

A new class of simple and highly sensitive piezocapacitive sensors that are capable of detecting static and dynamic pressure changes is reported. The pressure sensor structure is formed by vertically sandwiching a sandpaper-molded carbon nanotube/poly(dimethylsiloxane) composite (CPC) dielectric layer between two ion-gel thin film electrodes. Such a capacitive sensor system enables the distinguishable detection of directional movement of applied pressure as well as static pressure variation by modulating ion distribution in the ion-gel thin films. The resulting capacitive pressure sensors exhibit high sensitivity (9.55 kPa), high durability, and low operating voltage (0.1 V). Our proposed pressure sensors are successfully applied as potential platforms for monitoring human physiological signals and finger sliding motions in order to demonstrate their capability for practical usage. The outstanding sensor performance of the pressure sensors can permit applications in wearable electronic devices for human-machine connecting platforms, health care monitoring systems, and artificial skin.

Evaporation-induced electricity generation, harnessing natural vaporization of water, is spotlighted as a promising energy conversion system with showing off remarkable characteristics such as continuous generation without artificial water motions. However, the vague origin and mechanism of this phenomenon are obstacles for practical application. Herein, the origin of the evaporation-induced electricity generation was verified in terms of the "ionovoltaic" effect, ionic motion-induced charge carrier flows, through a resistance-controllable metal oxide platform. The device, composed of solvothermal-grown zinc oxide, showed output signals of ∼0.4 V and ∼20 nA. This study improves an understanding of the evaporative ionovoltaic mechanism and secures applicability to various materials for future energy conversion devices.

A multimodal microfluidic capacitive sensor for detecting lateral pressure movements and temperature variations is presented.