Abstract:

Objective As the key component for gas sensors, the development of gas-sensitive material has attracted much research attention. At present, research on gas-sensitive materials focused mainly on membrane structures, which has poor flexibility and reprocessability. Therefore, in order to meet different needs and expand the applications, this study proposes a one-dimensional structure gas sensor with better flexibility, deformation ability and textile processability.

Method Water bath electrospinning method was used to make the polyamide 6 (PA6) spinning solution with a mass fraction of 12% and 24 kV electrostatic voltage, among other experimental parameters. The micro-nano fiber composite yarn (MNY) with polyester (PET) as the core yarn and PA6 nanofiber as the coating layer was prepared, and the MNY/PANI composite conductive yarn was prepared by a continuous conductive treatment method based on in-situ polymerization. The effect of different reaction liquid concentration on the structure and performance of MNY were studied, and the optimal reaction liquid concentration was achieved for preparing MNY/PANI gas sensing elements. Compared with PET/PANI gas sensing elements under the same parameters, the difference in gas sensitivity effect between yarns with different structures was explored.

Results After studying the surface morphology of MNY and MNY/PANI, materials conductivity, infrared spectrum and gas sensitivity, analysis was carried out. The nanofibers on the surface of MNY were relatively complete, forming a good skin-core structure, and the nanofibers were smooth and orderly. The surface of the conductive-treated MNY/PANI composite conductive yarn was found to adsorb a large number of particles, and the density of adsorbed particles on the yarn surface increased as the concentration of reaction liquid was increased. With the increase of the concentration of reaction liquid, the conductivity of MNY/PANI composite conductive yarn increased first and then decreased, and the conductivity of MNY/PANI-3 reached the maximum value of 7.53 S/cm. The infrared spectra of PET, MNY and MNY/PANI-3 composite conductive yarns were tested and compared. Compared with PET without any treatment, the characteristic peaks of MNY prepared by electrostatic spinning technology appeared at 3 304, 1 672, 1 542 and 1 170 cm^-1. This indicated that the surface of MNY after electrostatic spinning was attached with amide group. In addition, MNY/PANI-3 also showed characteristic peaks around 1 611, 1 361 and 810 cm^-1, indicating that PANI/MNY-3 composite conductive yarn contained PANI. By comparing the response test of MNY/PANI-3 and PET/PANI composite conductive yarns prepared under the same reaction concentration parameter in NH₃ atmosphere, it was found that both reached the maximum sensitivity in the first test, which was 2.70 and 4.62 respectively, and then gradually weakened and eventually plateaued with the increase of the number of cycles. However, the sensitivity of MNY/PANI was consistently better than that of PET/PANI. The difference was that the response curve of PET/PANI had more fluctuations, while the response curve of MNY/PANI was smooth. In addition, with the increase of the number of tests, the response effect of MNY/PANI was better than that of PET/PANI, and the recovery time of MNY/PANI increased with the increase of the number of test cycles, but it was still much smaller than that of PET/PANI.

Conclusion After NH₃ detachment, the resistance value of PET/PANI in the air was much different from the initial resistance value, indicating that its reversibility is poor. After repeated testing of MNY/PANI, resistance of gas sensing elements in air could get better recovery, good reversibility and relatively small change in sensitivity. MNY/PANI gas sensor has higher sensitivity to NH₃ due to the high specific surface area of its nanostructure, which is due to the uniform distribution of small PANI particles adsorbed by the nanolayer. Therefore, it can show better response-recovery effect, better repeatability and stability, and has initially possessed the conditions as an excellent gas sensor, indicating the feasibility of one-dimensional structure gas sensor.

Key words: electrospinning, micro-nano fiber composite yarn, in-situ polymerization, gas sensing, NH₃ detection, fiber based gas-sensitive sensor