Preparation and performance of ion sensors based on composite nanofiber membranes

Objective In order to develop a flexible ion sensor with high stability and sensitivity, polyvinylidene fluoride ionic liquid ((PVDF)/IL) composite nanofibrous membranes were prepared by electrostatic spinning, and assembled with electrode materials to form an ion sensor with a sandwich structure. Method The effects of spinning liquid mass fraction and IL content on the spinning process and fibrous membrane morphology were investigated using scanning electron microscopy, and the elemental distribution and chemical structure of the composite nanofibrous membranes were characterized using energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The effects of nanofibrous membranes with different IL contents and thicknesses on the sensor performance were investigated using the flexible sensor test system (FSTS), and the ion sensors were attached to human skin and clothes for body signals and motion monitoring, and the real-time output electrical signals were recorded using the FSTS. Results When the mass ratio of PVDF was 18%-19% and the dosage ratio of ionic liquid was 2:1 and 3:1, the composite nanofibrous membranes had a regular surface, fewer beads, and a uniform distribution of fibre diameters. The addition of ionic liquid increased the number of charged ions in the PVDF nanofibre membranes and made them uniformly distributed. The pressure sensing sensitivity of the ion sensor in the detection range of 0-40 kPa was 32.471 pF/kPa at a PVDF mass fraction of 18% and an ionic liquid dosage ratio of 2:1. The increase in ionic liquid content in the composite nanofibrous membrane ion sensor resulted in a significant increase in the sensitivity of the sensor. As the thickness of the nanofibre membrane increases, the detection range of the sensor gradually increases and the sensitivity gradually decreases. The hysteresis of the ion sensor was 6.64% with no significant delay or dependence at different pressure levels, with compression rate of 5 000 loading cycles. Ion sensors attached to the surface of human skin and clothing was able to distinguish the motion of the human body by the output pressure-capacitance curves. Conclusion The composite nanofibre membrane-based ion sensor exploits the supercapacitive property of the electric double layer (EDL) to accurately detect small-amplitude human motion and large-amplitude joint motion. Meanwhile, the composite nanofibre membrane ion sensor has a pressure sensing with a sensitivity of 32.471 pF/kPa in the detection range of 0-40 kPa, maintains outstanding mechanical stability after 5 000 loading-cycles, has a low hysteresis rate (6.64%) and has no significant delay and dependence. The membrane can be applied in the future to communication with deaf people, human-computer interaction, intelligent control and other fields. © 2024 China Textile Engineering Society. All rights reserved.