Sandwiched-resistive sensors based on the 3D printing of TPU/CNTs–ILs

In this study, a TPU/CNTs–ILs flexible sensor with a sandwich structure is prepared by a combination of coating and 3D printing method. First, to promote the dispersion of carbon nanotubes (CNTs), 1-butyl-3-methylimidazole tetrafluoroborate ionic liquids (ILs) are used as modifier. Two layers of thermoplastic polyurethane elastomer (TPU) filaments are printed on the bottom plate via 3D printing and coated with a layer of CNTs–ILs as a conductive layer. Finally, two layers of TPU are printed to encapsulate the conductive layer. It is revealed that the printed TPU/CNTs–ILs flexible sensor exhibited a sensitive resistance response at small and large strains (GF value of 20 and 440 at strains of 5% and 50%, respectively) while retaining high mechanical strength (tensile strength of more than 30 MPa and 600% elongation at break). In addition, the fabricated flexible sensor still displayed good resistance response after being cyclically stretched in the range of 0–50% strain for more than 400 s. Comparing the signal response of different vocal cord vibration frequencies and loudness, it is shown that the flexible device with high sensitivity in sensing can monitor human motion behavior, indicating the TPU/CNTs–ILs flexible sensor with a sandwich structure has excellent application prospects as wearable electronic components. Graphical abstract Scheme 1. The graphic abstract of the whole experimental process