| Flexible capacitive pressure sensors can convert external force stimuli into capacitive signals while maintaining flexibility,which has great potential in human-computer interface,health monitoring,and electronic skin.This thesis focuses on the iontronic capacitive-type pressure sensor with porous composite ionic sensing layer.The influences of porosity and compression modulus of porous structure on the sensitivity of the iontronic pressure sensors were researched by using finite element simulation,experiment and sensing mechanism analysis.This study provides a new understanding of the sensitivity enhancement strategy for the iontronic capacitive pressure sensor,and also provides ideas and evidence for its application in wearable,coating and transparent sensing.The mechanical behavior of porous structure under compression is analyzed through mechanical mechanism and finite element method.It is found that the synergistic effect of compression deformation of porous structure and ionic characteristics of ionic liquid（IL）on EDL capacitance is the key to achieving high sensing performance.The porous structure with high porosity and low modulus can effectively improve the compressive deformation performance of the material,and enhance the change of the contact area between ionic-electronic interface,thus promoting the sensing performance of iontronic pressure sensors.Based on this idea,polyurethane（PU）-IL composite foam with a porosity of 95.4%and compression modulus of 3.4 k Pa was used as the ion sensing layer.The foam-based pressure sensor has a sensitivity of 9 280 k Pa-1,which is the highest of the current iontronic capacitive-type pressure sensors.The device also exhibits a fast response speed of 10 ms,high pressure resolution of 0.125%at 80 k Pa pressure and remarkable mechanical stability over thousands of compressing or bending cycles.Such sensor has a prominent capability in applications of water wave detection,underwater vibration sensing,and mechanical fault monitoring.Based on the design concept of porous composite ionic structure,this thesis directly uses porous textiles activated by IL as the ion sensing layer to develop a wearable textile sensor.This IL-textile can be activated in the target area specified of the dress,which contributes to fabrication and operation of the sensing device.The textile sensor not only has a high ability to sense tiny pulse signals but also maintains the flexibility and comfort of the original textile,which greatly improves the wearability of the device.In addition,a porous electrode with good mechanical stability was obtained relying on the mechanical properties of buckling of ultra-fine silver nanowire（Ag NW）.A multifunctional textile sensor with through-pore structure was prepared by combining porous electrode and porous cellulose acetate（CA）-IL composite membrane.The sensing device has a sensitivity of 4.46 k Pa-1 and response time of 39 ms,which can clearly collect various human motion and physiological signals,and exhibits waterproof,self-cleaning,and antibacterial,demonstrating wild application potential in smart health or exercise monitoring.In addition,this thesis explores the design of pressure sensing paint.By using polyimide（PI）as basic material and design of composite ion layers with porous structures,a high-temperature pressure sensing coating that can be coated like the paint was prepared.The sensing paint shows good conformability,and can be coated on the surface of various irregular structures compared with traditional packaged devices.After plasma treatment,the interfacial toughness between the bottom electrode layer and metal substrate is as high as 413 J/m2.The interfacial toughness of electrode layer and the sensing layer is greater than 127 J/m2,which does not use a binder for encapsulation,and represents self-adhesion.The sensing paint still shows good sensing performance at high temperature of 300°C and ultra-high pressure of 2.5 MPa.This coating method is expected to open a new way for integration of iontronic pressure sensors,and has shown a good application prospect in the fastener stress-relaxation monitoring system.The serious light scattering in porous substrate results in the sensing device cannot be sensitive and transparent at the same time.To solve this problem,we propose a way to select IL whose refractive index matches well with that of the skeleton to replace the air in the porous materials,which effectively keeps interface continuity and reduces the light scattering,and greatly improves the transparency of the composite ion layer to 94.8%.In addition,the surface still retains a few protrusions and the toughness is significantly improved in the composite ion structure,which can provide high transparent,flexibility and sensitivity of the pressure sensor.The flexible sensor has transparency of 90.4%,a sensitivity of 1.19 k Pa-1,a low detection limit of 0.4 Pa,and good mechanical stability,which is potentially useful as transparent touch screen and smart window.In this thesis,the mechanical principle of pressure sensing of the iontronic capacitive pressure sensor is analyzed,and the design method of the sensor based on the porous composite ionic membrane is proposed.The ultra-sensitive,wearable,coating,and highly transparent sensor is fabricated,which provides a new design strategy for the preparation and application of capacitive pressure sensors. |
