Preparation Of Flexible Mechanical Sensing Materials And Research On Device Performance

With the rapid development of flexible electronic devices,flexible mechanical sensing materials have attracted more and more attention.Especially with the rapid progress of society,the demand for flexible devices is becoming higher and higher.The existing traditional rigid sensors can no longer meet the needs of people.However,flexible sensors are in the initial stage in present.Limited by the slow development of material field,the existing flexible mechanical sensors cannot meet the requirements of application.In view of the shortcomings of the existing flexible mechanical sensing materials,the preparation strategies of various mechanical sensing materials were designed,and a variety of flexible mechanical sensors were constructed accordingly.Then the properties of the as-prepared flexible mechanical sensors were investigated and the sensing mechanism was explained in detail.Finally,based on the sensors with excellent performance,various human body signals from weak（arteriovenous pulsation,facial expression,etc.）to strong（joint bending）were detected.Each part of the paper is summarized as follows:1.In view of the problem that the existing flexible strain sensors cannot have both excellent tensile ability and high sensitivity,combined with the common slip mechanism and crack mechanism in mechanical sensors,a nanocomposite based on slipable layered structure was prepared using silver nanowires,graphene oxide and fullerenes.The device has good tensile ability（maximum 62%strain）and extremely high sensitivity（gauge factor above 400 in the strain range of 3%-62%）.This excellent sensing performance far exceeds that of other materials.Benefiting from the excellent performance,the device can detect wrist pulse signal,facial expression signal and wrist bending signal.2.The strain sensor based on slip structure prepared in the last research can not detect the bending of knee joint,which is mainly due to the slight deficiency of the tensile property of the device.In view of this problem,the theory of applying the mechanical toughening mechanism to the flexible strain sensing materials was proposed.A composite with multiple interfacial effects was prepared using silver nanowires,MXene,dopamine and nickel chloride.In this composite,dopamine and nickel chloride provide a large number of hydrogen bonds and coordination bonds.Its tensile ability is more than 80%.Its sensitivity is more than 8700,and it can withstand5000 cycles without damage.This excellent sensing performance enables it to detect human motion signals that can not be detected by other sensors,including the pulse of the human body in different motion states and the bending signal of the knee joint.3.In view of the poor sensitivity and range of work in flexible pressure sensing materials,the structure of common aerogel materials was analyzed.It was pointed out that the poor performance is due to the volume expansion in the normal direction during compression（positive Poisson’s ratio behavior）.To address this problem,an aerogel sensing material with negative Poisson’s ratio behavior was designed and prepared.This special phenomenon of negative Poisson’s ratio makes the sensing material have larger volume shrinkage behavior during compression,resulting in more contact of the pore walls.Due to this special property,the device can have high sensitivity(maximum gauge factor is 990.4 k Pa^-1)and large working range（working interval is 0-1.5 k Pa）,far more than other pressure sensing materials.4.The improvement of sensing performance through the structure regulation of aerogel has reached the extreme value.To further enhance the sensing performance of pressure sensing materials,innovation was made for the nano-level structure of sensing materials,and the flexible pressure sensing material design strategy of"3C"（Composite material,Channel structure,Cross-link interface）was proposed.According to this strategy,an aerogel pressure sensing material based on MXene and ultra-low modulus molecular chains was prepared.The pore wall materials that make up the aerogel have the sandwich structure of MXene and supramolecular.The pressure sensor exhibits ultra-low detection limit（0.0063 Pa）and ultra-high sensitivity(maximum gauge factor is 1929.8 k Pa^-1).Benefiting from the sensing performance far beyond other materials,the device can detect some extremely weak signals,including the human neck vein signal,mosquito take-off and landing signal and so on.