Construction,Structure Regulation And Mechanical Sensing Performances Of Flexible Conductive Polymer Gels

Flexible mechanical sensitive materials have a wide range of applications in flexible sensors,wearable devices,flexible robots and human-machine interaction,etc.because of their excellent bendability,foldability and stretchability.Compared with other flexible mechanical sensitive materials,conductive hydrogels are one of the key materials for constructing the next-generation flexible mechanosensors due to their excellent flexibility and biocompatibility.However,the existing conductive hydrogel materials have limited flexibility and significant hysteresis,and the flexible mechanosensors assembled from traditional conductive hydrogels generally exhibit low sensitivity and poor sensor-object fit,which limits the applications of conductive hydrogels in flexible mechanosensors.In this thesis,highly flexible and low hysteresis polyvinyl alcohol/polyaniline（PVA/PANI）hydrogels/organohydrogels were prepared by an in-situ oxidative polymerization and a cyclic freezing-thawing procedure using polyvinyl alcohol（PVA）,aniline（ANI）and phytic acid（PA）as raw materials.Gels with micro-convex structures and layered Janus structure were further constructed by a template method.Flexible mechanosensors were assembled using gels as the key sensitive materials and their sensing performances were investigated.The applications of mechanosensors in human motion detection were explored.The main research contents and results are as follows:（1）Highly flexible and low hysteresis PVA/PANI hydrogels with fully physically cross-linked structure were prepared by systematically regulating the content of flexible chains（PVA）and rigid chains（PANI）.Such hydrogels possess elastic modulus close to human soft tissues and strain hysteresis as low as 5%.High sensitivity（GF=4.28）and good stability（>1000 cycles）are achieved in hydrogel-based strain sensors.Organohydrogels were further constructed by introducing glycerol into the PVA/PANI hydrogels,which achieved good moisturizing performance and maintained good flexibility,electrical conductivity and sensing performance even when left at room temperature for 7 days.Finally,the strain sensors of PVA/PANI gels have achieved real-time monitoring of human activities such as joint flexion and swallowing.（2）PVA/PANI hydrogel electrodes containing micro-convex structures were prepared by a template method and"sandwich"capacitive pressure sensor were constructed.The influence of the component,thickness and micro-convex structure size of the gel electrode on the sensitivity of the sensor was systematically investigated.Due to the introduction of the micro-convex structure,the sensitivity of the sensor has been significantly improved to 7.7k Pa^-1.In addition,a capacitive pressure sensor was further constructed using organohydrogels as electrode to achieve pressure sensing at-18°C.This capacitive pressure sensors not only have the ability to monitor larger pressures such as joint flexion,but also detect tiny pressures such as blowing and brush writing.（3）Layered Janus hydrogels with single-sided adhesion were prepared by a cyclic freezing-thawing method.The layered hydrogels consist of a reversibly adhesive PVA/PA layer and a non-adhesive PVA/PANI layer.The flexibility of layered hydrogels can be modulated by the gel composition.The interfacial peeling force between PVA/PA layer and PVA/PANI layer is 114.6 N/m.The layered hydrogels were used to construct wearable hydrogel sensors,which achieve high sensitivity（GF=3.4）,low response time（loading:60 ms,unloading:62ms）and good reversible response（>1000 cycles）.In addition,the hydrogel sensor was further coupled with a Bluetooth wireless signal transmission system to build a wireless wearable sensor that can monitor human activities such as walking,squatting and stair climbing in real time and conveniently through an APP in a cell phone.