Printable Strain Sensors with Viscosity-Adjustable Ionic Liquids for Motion Monitoring.

Flexible strain sensors with ionic liquids have broad application prospects in various fields such as human-machine interaction, motion monitoring, and soft robots due to their conformability. The manufacture of strain sensors based on ionic liquids mainly relies on traditional molding methods and embedded 3D printing methods. However, these methods are complicated and involve lots of manual operations because of the strong fluidity of ionic liquids. In this paper, we propose the use of high conductivity ionic liquids composed of potassium iodide, glycerin, and polyethylene glycol (KI-Gly-PEG). All-in-one direct ink writing of ionic liquids is possible by adding functional materials into the KI-Gly system to change its rheological property and adjusting temperature during the process to assist in improving printing accuracy. We fabricated a flexible strain sensor with silicone rubber and KI-Gly-PEG solution by the all-in-one direct ink writing method. Further, we utilized the strain sensor to monitor the elbow bending angle by analyzing its resistance.