Preparation,Mechanism And Application Of Flexible Conductive Composite Materials And High-Performance Strain Sensors

In recent years,wearable flexible strain sensors have become one of the current research hotspots in the field of electronic materials due to their great application prospects in human activity monitoring,biomedical research,artificial intelligence,etc..In particular,the flexible resistance-type strain sensor（FRSS）can convert external mechanical stimuli into visual resistance change signals,and has the advantages of high sensitivity,fast signal response,low manufacturing cost,and good stability.It is considered to be the best choice for next-generation physical sensors.However,most of the reported sensors have problems such as high preparation cost,cumbersome process flow,and poor comprehensive performance,which make it difficult to achieve large-scale production and application.In this paper,through the innovative design of sensing materials and microstructures,a series of resistance-type strain sensors with excellent comprehensive performance are prepared by simple and easy methods,and they are applied to detect expression changes,speech,pulse,limb movement,breathing,and writing.The main research content and results of this paper include the following aspects:（1）Graphene oxide（GO）was uniformly deposited on the surface of the plasma-treated polyester fabric（PETf）by the dip-coating method.Subsequently,the thiolated graphene-coated polyester fabric（GSH@PETf）was obtained by the one-pot reduction method,and FRSS was obtained after multi-layer stacking and packaging.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Raman spectroscopy（Raman）,X-ray photoelectron spectroscopy（XPS）and four probe instruments were used to characterize the morphology,chemical structure and conductivity of GSH@PETf.The influence of multi-layer structure on the sensing performance of the sensor and the sensing mechanism were discussed.The results showed that the surface resistance of GSH@PETf was as low as 479.6Ω/sq,and the multi-layer structure can significantly improve the sensitivity and detection range of the sensor.the prepared strain sensor not only achieved a wide detection range（0-200 k Pa）and high sensitivity(8.36 k Pa^-1/0-8 k Pa),but also a faster recovery speed（87 ms）and good cycle stability.In addition,the sensor can accurately detect various human activities including pulse,body motion and pronunciation.The two-dimensional sensor matrix integrated by the sensors can also realize the mapping and recognition of spatial pressure distribution.（2）First,the cotton fabric was carbonized at high temperature to obtain carbonized cotton fabric（CCF）,and then soaked in the mixed n-hexane solution of vinyl terminated polydimethylsiloxane（V-PDMS）,trimethylolpropane triacrylate and 2-methylpropanone.After being taken out,UV curing was performed to prepare PDMS anchored carbonized cotton fabric（PACCF）,and then the FRSS with a large amount of air-gap structure was obtained after multi-layer stacking and packaging.XRD,FT-IR and SEM were used to analyze the chemical structure and morphology of PACCF.The relationship between air-gap structure and the sensitivity and detection range of the sensor was studied,other electromechanical properties of the sensor and its sensing mechanism were discussed,and its application in detecting various human activity was demonstrated.The results showed that the surface resistance of the PACCF was as low as 293Ω/sq.The sensitivity of the sensor increases greatly with the increase in the number of air-gap structures.The sensor based on the multilayer air-gap structure has a wide pressure detection range,high sensitivity(13.89 k Pa^-1/0-6 k Pa),short response time（64 ms）and excellent repeat stability.The sensor can be applied to detect pulse,airflow,weak vibration and various body movements,showing important application prospects in the field of electronic skin.（3）First,a mixture solution of hydrochloric acid and lithium fluoride was used to etch aluminum titanium carbide（Ti₃AlC₂）to obtain the Ti₃C₂Tx nanosheets（MXene）after ultrasonic and stripping.The PDMS film with spinosum microstructure was fabrcated by the template reproduction method.Subsequently,MXene@PDMS conductive films were prepared by dipping method,then the FRSS was fabricated after stacking and packaging two layers MXene@PDMS conductive films.The morphology,chemical composition of MXene and the morphology of MXene@PDMS film were analyzed with XRD,SEM,TEM,Raman,XPS,optical microscope and 3D profiler.The main factors for the sensitivity,detection range,and linearity of the sensor and its corresponding sensing mechanism were discussed and analyzed.The results showed that MXene with excellent conductivity was uniformly deposited on the surface of PDMS.Based on the hierarchical structure of the difference in the size of the upper and lower spinosums,the MXene@PDMS 280/1000sensor had high sensitivity(2.6 k Pa^-1),ultra-wide linear range（0-29.9 k Pa）,fast response time（40 ms）and excellent repeat stability.The sensor can realize real-time detection of various human activities,and the integrated sensor array can sensitively sense"point"pressure and"plane"pressure distribution,showing great application potential in the field of tactile perception.（4）Titanium carbide particles（Mp）were obtained by etching Ti₃AlC₂ with hydrofluoric acid.PDMS films with spinosum microstructure were prepared by template method,and MXene@PDMS film was prepared by multiple dip-coating.Subsequently,the reduced graphene oxide-coated PDMS（RGO@PDMS）was obtained after layer-by-layer assembly and hydrogen iodide reduction.Then,the Mp and Mn dispersions mixed with PEI were successively dripped and deposited on the surface of RGO@PDMS to obtain Mn/Mp/RGO@PDMS conductive film with interlocking spinosum microstructure.Finally,a new high-sensitivity strain sensor based on the bionic skin interlocking structure was obtained after stacking and packaging.XRD,SEM,EDS,XPS,Raman and other tests were used to characterize the chemical structure and micro-morphology of Mp,PDMS film,MXene@PDMS film and Mn/Mn/RGO@PDMS.The dispersion of PEI in the conductive layer of Mp and Mn was studied,the impact of the interlocking spinosum microstructure on the sensitivity and detection range of sensor,and related sensing mechanisms were discussed.The results showed that Mp had an“accordion”structure,PEI was evenly distributed in the conductive layer of Mp and Mn,and the bionic skin interlocking microstructure significantly improved the sensitivity of sensor.The sensor achieved an ultra-high sensitivity(29.3 k Pa^-1),a broad detection range（0-70 k Pa）,a fast response time（40 ms）,excellent stability and repeatability.The sensor can successfully detect various small-range human activities including pulse,breathing,and vocalization.The integrated sensor matrix can sensitively perceive the planar pressure distribution and detect the corresponding resistance changes of local pixels in real time.（5）The silver nanowires（AgNWs）were prepared by the polyol method,and the functional polyurethane elastomer（FPU）that can heal at room temperature was prepared by the one-pot two-step method,GO coated nickel foam（GO@NF）was prepared after multiple soaking and drying.Subsequently,hollow thiolated graphene foam（TGF）was prepared under the etching and reduction action of hydrobromic acid and thiourea,and the three-dimensional（3D）conductivity network of AgNWs coated TGF（AgNWs@TGF）was prepared by multiple dip-coating method.Finally,the AgNWs@TGF was completely embedded in the FPU elastomer by the vacuum method to obtain the room temperature self-healing FRSS.SEM,TEM,XRD FTIR,gel permeation chromatography（GPC）and proton nuclear magnetic resonance spectroscopy（1H NMR）were used to analyze the morphology and chemical structure of AgNWs and FPU,the influence of AgNWs load on the gauge factor of the sensor and its sensing mechanism and healing mechanism were discussed.Based on the high conductivity and excellent ductility of the 3D AgNWs@TGF binary network,and the good elasticity and self-healing properties of FPU,the prepared strain sensor exhibited excellent overall performance,including good stretchability（60%strain range）,high gauge factor（1.1-11.8 and detection limit of 0.1%strain）,fast response capability（response/relaxation time of 40/80 ms）,excellent fatigue resistance and excellent conductivity recovery characteristicsafter after destruction.And the sensor successfully detected various human activities including voice recognition,various joint motions and writing,showing huge practical application potential in special application scenarios such as medical care,smart writing,recognition and wearable electronics.