| Over the past decades,with the rapid development of artificial intelligence and wearable devices and other industries,flexible sensors have gradually become the focus of academic and industrial attention.Traditional sensors are made of rigid materials,which are hard and brittle,difficult to curl and fit well with human skin,and cannot meet the application in certain fields.The flexible strain sensor based on the polymer material with tensile ability has the advantages of good flexural flexibility,stretchability,lightweight texture and easy to carry.It has a wide application prospect in the fields of human movement monitoring,flexible electronic skin,biomedicine,human-computer interaction and so on.However,the conventional polymer-based piezoresistive flexible strain sensors have poor cyclic stability and insufficient stretching range during repeated loading due to the inability of the conductive particles to bond well with the flexible polymer substrate,which limits their use in flexible electronics.Therefore,from the point of view of material design and structural design,the preparation of piezoresistive flexible strain sensor which takes into account sensitivity,strain range and tensile cycle stability must be innovated.In order to solve the above problems,the electrospun fibrous membrane of thermoplastic polyurethane(TPU)was prepared as a flexible polymer substrate for the sensor by electrostatic spinning technology and controlled adjustment of the fiber diameter,and the flexible strain sensor was prepared by combining carbon nanotubes(CNTs)with the flexible polymer substrate by filtration.The scaffold structure of the electrospun membrane can be used as a carrier for the uniform attachment of conductive particles,and the well-dispersed nanoparticles can be more easily loaded by the pore size of the electrospun fiber membrane to build a conductive layer.TPU fibrous membrane,which increases the surface roughness of the fiber and improves the bonding ability between the flexible substrate and the interface of CNTs,ensuring the high sensitivity of the sensor while ensuring the large strain requirement of the sensor.Finally,two types of flexible strain sensors,CNTs/TPU and CNTs/DA/TPU,were prepared,and the effects of different mass fractions and different rotational speeds on the microscopic morphology of the prepared TPU electrospun fibrous membranes,the effects of rotational speed and CNTs filtration content on the microstructure,mechanical properties and sensing properties of the flexible strain sensor were investigated.The effects of the presence of polydopamine layer on the microstructure,mechanical properties and sensing properties of CNTs/TPU sensors were studied,the content of CNTs was analyzed by theoretical studies and thermogravimetric tests,the changes of resistance and strain during the stretching process were described by a mathematical model constructed by tunneling theory,the explanation of high sensitivity is given by analyzing the number of conducting paths and the distance between neighboring conducting particles.The results of the study are as follows: the TPU electrospun fiber membrane prepared at a mass fraction of 20 wt% and a receiving drum speed of 100 r/min has a wide fiber diameter distribution and a stable fiber support structure,and has the most excellent mechanical properties,with tensile strength and maximum tensile strain are6.49 MPa and 632%,and the strain sensor prepared by coating the TPU fiber with a polydopamine layer has a high sensitivity under stretching(200%).It has high sensitivity under tension(10528.53 at 200% strain),fast response time(188-221 ms),wide sensing range(up to 200%),good stability and durability.The sensor can be used as a human motion detection device for the movement of various parts of the human body and voice for accurate and stable electrical signal output,the final prepared sensor of this experiment is good to meet the comprehensive use requirements. |
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