| Flexible pressure sensors with good flexibility,ductility,conformability,portability and wearability have recently gained increasing attention because of their potential applications in electronic skin,human health monitoring,soft robots,human-computer interaction devices.In particular,piezoresistive pressure sensors have attracted more attention due to easy signal collection and relatively simple manufacturing process.However,most of traditional piezoresistive pressure sensors cannot meet the measurement requirements of weak signals due to their poor sensitivity.In recent years,researchers have greatly improved the performance of pressure sensors by introducing microstructures into the sensors.However,the fabrication of most microstructured pressure sensors requires expensive equipment,long processing time and complicated manufacturing processes,which greatly limits the large-scale production and wide application of flexible piezoresistive pressure sensors.To address the problems mentioned above,this thesis proposed two simple,low-cost methods for fabricating microstructured flexible pressure sensors,and systematically investigated the preparation and properties of microstructures and conductive layer integrated in the flexible pressure sensors,and demonstrated the performance and applicabilities of the flexible pressure sensors.The main works include two parts:(1)A simple fabrication method for a flexible pressure sensor based on carbon nanotube(CNT)-coated elastomer micropillar arrays was proposed.In this method,a magnetic-field-induced self-assembly combined with a magnetic polydimethylsiloxane(PDMS)composite spraying was used to facilely prepare high aspect ratio elastomer micropillar arrays,and then CNTs were deposited on the surface of the micropillar structures by the drop-coating method to serve as a conductive layer.Finally,the flexible pressure sensors were sealed with PDMS.The whole fabrication process of the flexible pressure sensors does not require expensive equipment and rigorous conditions.Furthermore,the high aspect ratio elastic microstructures of the sensors greatly broadens the range of pressure response,which is favorable to a wide range of applications with a single sensor.In order to optimize the manufacturing process of the sensor,the effect of different processing parameters on the geometric dimensions of the microstructures and the performance of the pressure sensor were systematically investigated.The results show that the sensitivity of the pressure sensor prepared by the optimized process is?0.497±0.005 kPa-1,and it has a wide pressure response range(10 Pa to 80 kPa),a response time<0.2 s,and good stability(>2000 cycles).The fabrication method of flexible pressure sensors has several advantages such as low cost,high efficiency,and scalable production.In addtition,the prepared sensors can detect various forms of force,including pressure,bending force,and twisting force.At the same time,it can be used to monitor human pulse,body movement,and vocal voice vibration signal.(2)A simple fabrication method for a flexible pressure sensor based on silver nano-film coated hierarchical microstructures was proposed.In this method,a micro-hole array mold combined with partially cured PDMS casting was used to form a flexible substrate with integrated microdome arrays,then the microdome array substrate was stretched and treated with plasma to produce a flexible substrate with a microdome/wavy hierarchical microstructures.Next,a silver nanofilm was prepared at the air/water interface by combining a phase change lysozyme nanofilm with a silver mirror reaction,which was then transferred to the surface of the prepared flexible substrate as a conductive layer.Finally,the flexible pressure sensor was encapsulated with PDMS.The thesis systematically investigated the effect of the process parameters on the geometries of microstructures and the performance of the sensors.The results show that the sensitivity of the hierarchically microstructured flexible pressure sensors is?1.291±0.001 kPa-1,and the response and recovery times are 70 ms and 160 ms,respectively.They can detect pressures from 10 Pa to 40 kPa and have good stability.Compared with the previous uniform microstructure pressure sensors,the hierarchically microstructured pressure sensors have higher sensitivity and response rate.Furthermore the silver conductive layer prepared with the phase change lysozyme nanofilm can firmly adhere to the PDMS film surface,which can be enhanced the stability of the conductive layer and is favorable to improve the durability of the sensor.Preliminary applications shows that the sensor can detect weak pressure(water droplets)and non-contact pressure signals caused by gas flow and human breathing. |
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