| With the popularity of various smart terminals,flexible wearable electronic devices have presented a huge market prospect.Flexible sensors will greatly affect the structure-functional design and future development of intelligent electronic devices as the vital components.Flexible composite materials are commonly applied in flexible sensors,and the crack structure based flexible force sensitive composites attract extensive attention owing to its ultrahigh sensitivity.However,the detection strain range of strain-sensitive crack-based composite is quite narrow in common,and the function of the pressure-sensitive composite is relatively simple,which limits their promotions and applications in the field of intelligence immensely.In this paper,electrospun thermoplastic polyurethane(TPU)is used as the substrate,and CNT/TPU conductive fibrous film is obtained by constructing a carbon nanotube(CNT)conductive layer on the TPU substrate.The sensitive conductive network is constructed through the conductive layer crack structure to prepare high-performance strain-sensitive composite and pressure-sensitive composite.The strain-sensitive response behaviors and mechanism of composites under various tensile and bending modes and the pressure-sensitive response behaviors and mechanism of composites under various compression modes,were studied;the application of crack-based flexible force-sensitive composite in physical vibration and human motion behavior detection is explored.The specific research contents are as follows:1.Preparation and properties of crack-based CNT/TPU strain-sensitive composite(1)First,CNT/TPU conductive fibrous film is fabricated through spraying CNT conductive ink onto the electrospun TPU fibrous mat.Crack-based CNT/TPU flexible strain-sensitive composite is prepared by pre-stretching the CNT conductive layer of CNT/TPU conductive fibrous film,and equilibrium the restrict relationship between strain response range and sensitivity under the strain stimulus by crack structure.The influence of the experimental parameters of the thickness of sprayed CNT conductive ink layer and the required pre-stretching strain to the microstructure and corresponding properties of the material are studied.(2)The stretching and bending properties of strain-sensitive composite are characterized in detail.It exhibits that the strain-sensitive composite combined features of high sensitivity in a greatly widened workable sensing range(Gauge factor(GF)of 428.5 within 100%strain,9268.8 for a strain of 100%-220%and larger than 83982.8 for a strain of 220%?300%),a fast response time(about 70 ms),superior durability(>10000 stretching-releasing cycles)and excellent response towards bending.(3)The excellent sensing performance of the strain-sensitive composite is related to the microstructural of CNT branches extended from two edges of the cracks and the excellent stretchability of the electrospun TPU fibrous mat(electron transfer benefit from the extension of the CNT from two edges of cracks,and it is beneficial to improve the sensitivity of the strain-sensitive composite,excellent stretch properties of TPU electrospun fibrous mat is beneficial to improve the strain detection range of strain-sensitive composite).The resistance model of electron transmission is preliminarily constructed and the resistance response changes under different conditions are analyzed by combining the characterization of the crack structure,which corresponding to the strain-sensitive composite and the crack morphology during the tensile process,the changes of relative resistance response under different conditions are studied,conductive mechanism of crack-based CNT/TPU strain-sensitive composite under stretching and bending conditions is understandable.(4)The practical applications of the strain-sensitive composite are studied.It proves that strain sensor based on the strain-sensitive composite can accurately detect the physical vibrational signal of the sound from mobile phone speaker and the oscillating signal of the steel ruler.Hand back when the hand is grasped,finger,wrist and elbow joint bending,knee flexion,wrist pulse beat and throat vocalization can be monitored in real time,demonstrating its potential application for smart devices,electronic skin and wearable medical monitors and so on.2.Preparations and properties of different structure of CNT/TPU pressure-sensitive composite(1)Construct crack structure is applied to the preparation of a highly sensitive pressure-sensitive composite in this chapter.The CNT/TPU concductive fibrous film is assembled in different ways.Three kinds of pressure-sensitive composites are fabricated combined with polyurethane(PU)film,which are CNT/TPU two-layer pressure-sensitive composite,crack-based CNT/TPU two-layer pressure-sensitive composite and CNT/TPU three-layer pressure-sensitive composite respectively.(2)The morphologies and structures of pressure-sensitive composite are characterized.The resistance response mechanism of the crack-based CNT/TPU pressure-sensitive composite under various compression conditions based on the simple conductive schematic of the crack structure is analyzed.(3)The resistance sensitive response of the crack-based CNT/TPU pressure-sensitive composite and the CNT/TPU three-layer pressure-sensitive composite under various compression conditions is explored and compared.It demonstrates that different rates of applied pressure have no effect on the output signal of pressure-sensitive composites' relative resistance responses.The relative resistance responses of pressure-sensitive composites can be distinguished under different pressures,and both of them have excellent durability and stability.Especially,the crack-based CNT/TPU two-layer pressure-sensitive composite exhibits lower pressure detection limit,the CNT/TPU three-layer pressure-sensitive composite exhibits better stability.It provides a good experimental basis for applying in intelligent display terminal equipment of pressure-sensitive composites.(4)The applications of pressure-sensitive composites are studied.Pressure sensors based on the pressure-sensitive composites,and the contact angle of the pressure sensor sample is tested(116.011°)to prove that pressure sensors have waterproof performance to a certain degree.The applications of the pressure sensor in human motion detection are explored,it demonstrates the broad applications of pressure-sensitive composites in the field of flexible wearable devices and various intelligent terminals. |
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