| Flexible mechanical sensor is a device that can transform mechanical stimulation into detectable electrical signal.It has excellent flexibility and mechanical properties.It has important application prospects in the fields of flexible robot,wearable device,man-machine interface and so on.The mechanical flexibility of such sensors mainly comes from flexible sensitive materials.Therefore,the construction of high-performance flexible sensitive materials is the key to the development of new flexible mechanical sensors.However,the preparation of flexible sensitive materials by coating,filtration and other methods is complicated and the inability to accurately control the microstructure of the materials leads to limitations performance.It is of great research value to use new preparation techniques to modulate the micro/nano structure and improve the mechanical sensitivity of materials.In this paper,cellulose acetate（CA）and thermoplastic polyurethane（TPU）are used as flexible materials,and the flexible nanofiber membrane is constructed by electrospinning.At the same time,functional components are introduced into the nanofiber membrane to realize its response to mechanical stimulation,and the application of nanofiber membrane in piezoresistive pressure sensor,capacitive mechanical sensor and piezoelectric mechanical sensor is explored.The main research contents and results are as follows:（1）CA/PANI nanofiber membranes were prepared by electrospinning.The effects of the ratio of acetone to N,N-dimethylformamide and the content of cellulose acetate on the spinning process and fiber morphology were systematically studied.Therefore,we found that when the ratio of acetone to N,N-dimethylformamide was 2:1 and the cellulose acetate was 13 wt%,the solvent volatilization rate was the most appropriate during spinning,and the morphology of the fiber membrane was good.Then,the prepared nanofiber film was immersed in aniline solution,and polyaniline was introduced by in-situ polymerization on CA nanofiber film with hydrochloric acid as dopant and ammonium persulfate as oxidant.Due to the high porosity and nanofiber structure of CA/PANI film,when pressure is applied or bent,the internal conductive path of the fiber film changes,resulting in the change of resistance,which gives the fiber film good mechanical response.The sensor constructed by CA/PANI composite nanofiber membrane has high sensitivity of 3.02 k Pa-1,sensing range of 0～73.4 Pa and response time of0.35 s.It can be used for human motion monitoring.（2）The"sandwich"structure nanofiber membrane was prepared by electrospinning.The effects of the content of TPU and MXene on the fiber morphology,electrical conductivity and mechanical properties of nanofiber composite films were systematically studied.Therefore,we found that when the TPU is 12 wt%,the MXene is 4 wt%and the Ag NWs is 2 wt%,the obtained films have good morphology,electrical conductivity and excellent mechanical properties.The film has excellent mechanical properties and stress stimulation sensitivity,and can be used in the construction of high-performance sensors.The e-skins achieve a gauge factor（GF）of 1.21 in the strain range of 0-30%and 0.92 in the strain range of 30%-150%,a response time of 210 ms and 280 ms respectively during loading and unloading process,excellent sensing stability in about 2000 cycles.In addition,the e-skins also respond efficiently to pressure with a GF of 0.029 k Pa-1in the pressure range of 0-10 k Pa and 0.015 k Pa-1in the strain range of 10-70 k Pa and exhibit outstanding sensing stability in about 2000 cycles.This mechanical sensor can be used to monitor strain,pressure and human movement in daily life.（3）Hybrid films composed of PVDF coated TPU nanofibers were prepared by coaxial electrospinning.The effects of the content of TPU and PVDF on the fiber morphology and mechanical properties of the films were systematically studied.The effects of the content of TPU and PVDF on the fiber morphology and mechanical properties of the films were systematically studied by coaxial electrospinning.Therefore,we found that when the TPU solution is 12 wt%and the PVDF solution is 12 wt%,the TPU/PVDF composite fiber film has good morphology and excellent mechanical properties.The core-shell structure nanofiber membrane is used to construct a mechanical sensor,with a sensing range of 0.2～5 k Pa,high sensitivity of 0.42 V/k Pa,response time of 100 ms and good stability（>20000 cycles）.It can be used for the monitoring of human motion joints such as fingers,wrists,elbows and physiological activities such as speaking,drinking and eating. |
