Study On Flexible Conductive Films Based On Carbon Nanomaterials And Their Strain Sensing Performance

With the development of wearable electronic devices in the fields of intelligent robot,human movement/health monitoring and human-computer interaction,flexible strain sensors,as important signal reception and conversion units,have gained wide attention in industry and academia.In recent years,conductive polymer composites(CPCs)are regarded as the ideal material for flexible strain sensor,which consist of conductive fillers and polymer matrix.Among them,carbon nanomaterials are widely used as conductive fillers due to their advantages of excellent conductivity and workability.However,few CPCs based on carbon nanomaterials possesses high sensitivity,wide strain response range and fast response speed simultaneously due to the poor dispersity of conductive fillers and weak interaction between conductive fillers and polymer matrix,which limit their application in flexible strain sensors.To further improve the sensing performance of CPCs based strain sensors,in this paper,the following research was carried out according to the factors affecting the sensing performance of CPCs based on carbon nanomaterials,especially dispersity of conductive fillers and preparation method of CPCs:(1)Cellulose nanofibril(CNF)was utilized to disperse carbon nanotubes(CNTs),and the CNF/CNTs dispersion was prepared for the fabrication of CPCs.The effect of CNF with different carboxyl content on the dispersity of CNTs was studied.(2)CNF-CNTs/TPU composite films were fabricated by pumping the CNF/CNTs dispersion into the prepared electrospun thermoplastic polyurethane(TPU)film through vacuum filtration,and the influence of dispersity of CNTs on the strain sensing performance and morphology of CNF-CNTs/TPU composite flims was investigated.In addition,the strain sensing behavior,sensing mechanism and application of CNF-CNTs/TPU composite flims were studied.(3)The GE/TPU conductive composite films were rapidly prepared by spraying the graphene conductive ink onto the electrospun TPU films.The effect of different spraying time on the strain sensing performance of GE/TPU composite films was investigated.And strain sensing behavior,morphology,sensing mechanism and application of GE/TPU composite films were studied.The research results are as follows:1.CNF with high carboxyl content can effectively improve the dispersity of CNTs in aqueous systems.The concentration of CNTs in CNF/CNTs dispersion got higher with the increase of carboxyl content of CNF,which was 42.7?94.3?136.8?170.6 mg/L respectively.And Zeta potential of the prepared CNF/CNTs dispersion was less than-30 m V,demonstrating good stability.2.The enhancement of the dispersity of CNTs had an important impact on the sensing performance improvement of CNF-CNTs/TPU composite films.CNF-CNTs/TPU composite films exhibited ultrahigh gauge factor of 3361.9 and wide workable sensing range of 303%.In addition,it could suffer 1000 times of stretch-release cycles under strain of 100% and its response time for tiny strain was only 40 ms,exhibited ultrahigh sensitivity,wide workable sensing range,fast response speed and good stability.The sensing mechanism of CNF-CNTs/TPU composite film mainly depends on the tunneling effect between adjacent CNTs on the electrospun TPU substrate and the crack propagation on CNF-CNTs conductive layer during the stretching process.For practical application,the CNF-CNTs/TPU composite film was highly sensitive and stable for sound vibration from loudspeaker,ruler vibration,throat pronunciation,chest expansion,bending of finger and knee.3.The strain sensing performance of GE/TPU composite films could be effectively adjusted by controlling the technical parameters.With the extension of spraying time,the workable sensing range of the prepared GE/TPU composite film expanded.When the spraying time was 9s,the maximum gauge factor of GE/TPU composite film was 223.2,and the workable sensing range was 332%,which exhibited the best performance among the prepared GE/TPU composite films.In addition,the response time for stretching process was about 290 ms while the response time for releasing process was about 360 ms.It could suffer 1000 times of stretch-release cycles under strain of 150%,demonstrating excellent durability and resistance stability.The sensing mechanism of GE/TPU composite film mainly relies on the crack propagation of graphene coating layer.Besides,GE/TPU composite film could effectively monitor the pressure-release cycles of ruler,throat pronunciation,clenching of fist,and bending of wrist.