Preparation Of Silver Nanodendrites For Printed Stretchable Strain Sensors Application

In recent years,flexible and wearable resistive-type strain sensors have attracted a great deal of attention because of their substantial applications prospect in human motion monitoring,e-skins,and human-machine interaction intelligence systems.Recent efforts have been devoted to achieving both high stretchable(>55%)and high sensitivity strain sensors to satisfy the full range of human motion monitoring via various techniques.To date,reported methods such as spin-coating,dip-coating,injection,and vacuum filtration have some limitations in practical application because of their relatively complex production processes and the inability to quickly mass produce.By contrast,the screen-printing technology is not only low in cost,simple in operation,but also capable of patterning and rapid high-volume production.Therefore,screen printing technique is expected to accelerate the development of wearable strain sensors.In addition,the conductive filler used for the sensing layer of the resistive-type strain sensors mainly includes metal-based nano-materials and carbon-based materials.Among them,the silver nanodendrites possess a unique dendritic bifurcation structure,which have more contact points with each other,so a higher electrical conductivity can be obtained by the silver nanodendrites at a lower sintering temperature(80?).The silver nanodendrites has a large surface area and a large contact area with the substrate,and can withstand greater stretch strain.Therefore,silver nanodendrite is an ideal material for high stretchable,high sensitivity,and low energy consumption stretchable strain sensors.Moreover,there is no related research to use silver nanodendrites for strain sensors.In view of this,this paper synthesizes silver nanodendrites with uniform morphology and use it to formulate conductive ink.The all-printed resistive-type stretchable strain sensor is printed on the nitrile rubber substrate by screen printing.The main research results of this paper are as follows:A simple one-step displacement reaction is used,with silver nitrate as the silver source,copper foil as the reducing agent and polyvinylpyrrolidone(PVP)as the blocking agent.When the mass ratio of silver nitrate to PVP is 1:5,the silver nanodendrites with uniform morphology(main trunk dendrite size 8-12?m)are prepared.The effects of different average molecular weights and relative concentrations of PVP on the morphology of silver nanodendrites are studied.Silver nanodendrites with uniform morphology is used as conductive filler,polymer of styrene and 2-methyl-1,3-butadiene(SIS)solution is used as binder,and Disponer 904S is used as auxiliary agent for conductive ink.When the solid content is50 wt.%,the conductive ink exhibits good printability and can be printed on a variety of flexible substrate materials.After sintering at 80°C,the printed conductive tracks exhibit high electrical conductivity(1.14×10⁵ S m^-1)and excellent mechanical electrical properties(resistance increases by only 13%after 2500 bending cycles,and it is still able to maintain the conduction of the conductive path under stretch strain of160%).All-printed resistive-type strain sensor is produced by printing silver nanodendrites conductive ink on a nitrile rubber film by a simple two-step printing method.The effects of different sensing layer geometric patterns on the sensing performance of resistive-type strain sensors are analyzed in detail.The internal mechanism leading to the change of resistance of strain sensors is studied.Among them,the linear-type strain sensor with a line width of 2 mm exhibits a large strain working range(105%),high sensitivity(GFs=294.8),ultra-fast response speed(18 ms)and long-term air stability(greater than 3 weeks).Finally,we apply the silver nanodendrites based all-printed strain sensor to monitor human joint motion and gestures,demonstrating the potential of application in human motion monitoring and human-computer interaction.