Preparation And Application Of Flexible Piezoresistive Sensor Based On Electrospun Membrane/Polyaniline

With the development of modern information technology,people have higher and higher requirements for safe,reliable and convenient wearable electronic devices.Over the past two decades,wearable devices have received a lot of attention from scholars in the fields of energy supply,charge storage,electronic display and signal detection.The flexible piezoresistive pressure sensor,which can monitor the motion index and pulse parameters of human body,is undoubtedly the most representative among the researches of signal detection equipment.Piezoresistive sensor has simple structure,high precision and good durability.Structure of the device changes under external pressure,leading to changes in internal electronic components conduction path,which changes the overall resistance of the device.Therefore,according to the pressure and electric current（or resistance）of the coordinates,the pressure sensing curves can be drew point by point to find corresponding relation between the current and pressure.In addition to reducing test error,the flexible piezoresistive sensor also has a satisfactory mechanical property and lightweight,which shows important research value in the field of individual instant medical detection and early disease prevention.However,the flexible pressure sensor still has some shortcomings,such as low sensitivity,small linear detection range and poor response stability,which is greatly restricted in many specific applications.The sensitivity and linear detection range of the sensor are continuously optimized through developing various new three-dimensional（3D）structure by researchers.For example,the active material is loaded into the flexible porous substrate,the 3D conductive network deforms under the external pressure,and electrical signal fluctuates according to the change of electrical conduction path.The obtained sensor has good mechanical deformability.However,the uniformity of the active material in the 3D structure is poor,so the equipment error is significant,and detection accuracy is unstable.A flexible piezoresistive sensor with a special surface is fabricated by replicating a prefabricated template with a special microstructure to transfer the microstructure to a specific flexible substrate,and then the conductive layer is arranged to activate the substrate surface.The obtained sensor has high precision and good reliability.However,the natural template has an unregulated single shape,and the acquisition of artificial template leads to high energy consumption and uncontrollable cost,so it is difficult to achieve industrialization.On the other hand,the addition of irritant materials causes biosafety problems,the lack of effective permeability prevents skin respiration,and leads to various skin reactions,exposing the safety risks of flexible medical equipment to the forefront.By preparing porous materials and reducing the thickness of the equipment,the physical stimulation of sensor to human skin can be alleviated.Then,by selecting non-toxic,harmless and skin-friendly materials,the chemical stimulation of sensor to organism can be reduced effectively.These strategies have been proved to be effective ways to solve the hidden dangers of safety and comfort of flexible piezoresistive sensors,and provide reliable theoretical verification and operational technical basis for the development of wearable electronic devices.In this paper,three kinds of flexible piezoresistive sensors with different structures were designed and fabricated.Electrospun network was used as the flexible substrate,polyaniline（PANI）was used as the active conductive material,and bio-polysaccharide k-carrageenan（KC）was used as encapsulation for the built-in sensor.The sensitivity and detection range of the sensor were improved significantly by 3D porous structure.Air permeability and wearing comfort were enhanced by the existence of internal pores in the nanomesh.Bio-polysaccharide encapsulation layer shows good biocompatibility,degradability and excellent mechanical property,which provides a new options for the safety of flexible intelligent materials.The specific work is as follows:1.Preparation and application of piezoresistive sensor based on 3D skeletonIn this study,silk fibroin（SF）,polylactic acid glycolic acid（PLGA）,and PANI were used as raw materials,mixing electrospinning method was adopted to build the 3D skeleton sandwich structure skin sensor.By optimizing the concentration of PANI,the type and concentration of KC,it was found that the performance of the sensor was the best(2.54 k Pa^-1)when the amount of PANI was 4 g.In addition,the mechanical property of KC encapsulation crosslinked with 0.05 M Ca²⁺was the best.The 3D skeleton sensor can be used to detect the pulse fluctuation and joint movement of human.Furthermore,this 3D skeleton sensor shows a good air permeability,remarkable degradability,which is in line with the concept of green and sustainable development.2.Preparation and application of piezoresistive sensor based on microspheres networkIn this study,SF/PLGA（SP）electrospun composite fibers were used as flexible substrates,and PANI/Si O₂（PS）conductive microspheres were used as the active material.Corrugated multilayer microspherical sensor was constructed by using the interval spraying method.By optimizing the size of Si O₂ and spraying interval of PS microspheres,it was found that the morphology of PS conductive microspheres prepared by 20μm Si O₂was the best.After the optimal size of the conductive microspheres was determined,the spraying interval time was optimized.The best performance of the sensor was obtained by spraying the conductive microspheres on the electrospun film every 5 minutes(0.071k Pa^-1,0-380 k Pa).Corrugated multilayer microspherical film was encapsulated by bio-polysaccharide KC.The obtained sensor shows an excellent air permeability,and can be degraded and recycled in 90℃hot water.In addition,this sensor can be used to develop a variety of artificial intelligence applications.3.Preparation and application of piezoresistive sensor based on sheath-core fibersIn this study,a novel gas-liquid interfacial polymerization at low temperature was developed.Volatility of aniline（ANI）monomer was used,the fibrous membranes were pre-soaked in the mixed solution of initiator and dopant,and the PANI grown vertically along the surface of the electrospun fibers.The obtained sheath-core conductive fiber was assembly into sandwich structure to prepared piezoresistive sensor.By selecting the flexible substrate,and using glycerin to regulate the growth degree of PANI,the performance of the device can be optimized.The best performance of the sensor was obtained by using polyethylene terephthalate（PET）as electrospun substrate for polymerization,and the addition of 40 wt%glycerin could maximize the sensitivity of the sensor(10.62 k Pa^-1).The original large aperture and high space utilization ratio of the electrospun fibrous membrane can be maintained to a great extent with interfacial polymerization This method endows the electrospun fibrous membranes conductivity without sacrificing the 3D porous structure.The obtained sensor has good permeability and comfort,and can be used for respiratory detection and intelligent trajectory tracking.In conclusion,in this paper,conductive membranes with different 3D structures were prepared by electrospinning,and bio-polysaccharide encapsulation layer was used to improve the sensing performance of devices on the premise of ensuring breathability,comfort and safety.The 3D skeleton sensor has good sensitivity and wide detection range(2.54 k Pa^-1,165.3 k Pa),corrugated multilayer microspherical sensor can further improve the detection range（380 k Pa）,and the sheath-core fibrous sensor has the highest sensitivity(10.62 k Pa^-1).The three kinds of sensors can be applied to human health detection,language encrypted transmission and a variety of intelligent applications,which provides a new preparation strategy and application prospect for the structural design and application of pressure sensors.