Title:preparation Of Binary Nanosilver Nanocomposites And Their Application In Flexible Strain Sensors

With the rapid development of smart devices,the market for flexible strain sensors is also growing,such as wearable sensors,intelligent display theft packaging and so on.Currently,most flexible strain sensors are made of a "sandwich" structure,consisting of a conductive filler,a flexible substrate and an insulating protective layer.Nano-silver has been widely used as a conductive filler for flexible strain sensors due to its properties of both metallic silver and nanomaterials,and it is a worthy research topic to optimize its morphology and structure to prepare new composite materials and then regulate the performance of the sensors.In this paper,we investigate the application of binary nano-silver composite structures based on controllable prepared nanowires(AgNWs)for flexible strain sensors,with the following main findings:Firstly,AgNWs were prepared by the solvothermal method,and the ratio of additive to AgNO3 was optimized to achieve the best AgNWs with an average diameter of 42.1 nm and a purity of 96.59 wt%.On this basis,the binary silver nanoparticles(Ag NPs)with a particle size of 40-60 nm were successfully grown on AgNWs by optimizing the UV light illumination time and the mass ratio of AgNWs/AgNO3.The formation mechanism of the binary silver nanoparticles is as follows:Ag+forms primary particles on the surface of AgNWs,then grows and penetrates into AgNWs by diffusion mechanism,followed by Ag+aggregation on the primary particles to form secondary particles,and finally grows into Ag NPs.The resulting Ag NPs have no obvious boundaries with AgNWs,making the composite structure more stable and can be used as conductive fillers for flexible strain sensors.Secondly,aqueous binder and binary silver nanoparticles were used to prepare different types of flexible strain sensors.It was found that aqueous polyurethane(WPU)was suitable for tensile strain sensors,aqueous dispersion of acrylonitrile copolymer(LA133)for bending strain sensors and a mixture of LA133 and WPU for torsional strain sensors.The sensing range of the tensile strain sensors decreases with increasing binary nano-silver content,with the tensile strain sensor L-WPU-0.8%having the best overall performance with a sensing range of 5%to 90%and a sensitivity of 9.96.The stability of the torsional strain sensors increases with increasing binary nano-silver content,with the torsional strain sensor N-WPU/LA133-1.8%having the best sensitivity at a large torsional angle(180°).The current remains stable after 100 cycles at a large torsion angle(180°).The bending strain sensor W-LA133-1.8%has the highest sensitivity of 234.28 at a bending angle of 30°;the bending strain sensor W-LA133-0.8%shows a more regular current change rate at different bending angles and has the best sensing range and the best stability was achieved.Finally,the optimised flexible strain sensors were applied in practice.The results show that the tensile strain sensor L-WPU-0.8%can effectively detect human finger movements,and its current value can recover after 80 consecutive bends with high stability;the torsional strain sensor N-WPU/LA133-1.8%can discriminate the human body from ball movements based on the electrical signal;the bending strain sensor W-LA133-0.8%can be used to prepare an intelligent display stealing open package.The sensor can detect the sensing signal when the package is opened at different angles and can effectively monitor the "open" and "closed" status of the package.In this paper,different types of flexible strain sensors were prepared using AgNWs/Ag NPs binary nano-silver composite structures as conductive fillers and aqueous resin as the binder phase.