Low Temperature Joining Of AgNW Networks And Performance Of AgNW Transparent Electromagnetic Shielding Films

Silver nanowire(AgNW)films are considered as the best alternative to indium tin oxide(ITO)transparent conductive films due to their potential excellent conductivity,light transmittance and flexibility.However,the enhancement of the conductivity of the film by increasing the density of AgNWs will inevitably lead to a decrease in the light transmittance.Therefore,in order to improve the overall transparent conductive performance of AgNW films,it is necessary to consider the AgNW size,distribution and connection of the nanowire joint.In this paper,the distribution of AgNWs were designed and optimized,and the AgNW joints were post-treated.Then monolayer AgNW mesh films with excellent transparent and conductive comprehensive properties were obtained.After that,the optimized monolayer film was applied in the multilayer structure,the flexible transparent electromagnetic shielding film with excellent properties was prepared,and its shielding mechanism was studied.In this paper,the improved polyol method was used to prepare AgNWs with different aspect ratios by adjusting the process parameters,and the effect of AgNW size on the transparent conductive properties of the film was studied.With the increase of the aspect ratio of AgNWs,the number of AgNWs joints decreases,and the transparent conductivity of the obtained films increases.When the aspect ratio of AgNW used increased from 140 to 777,the light transmittance of the film will rise from 66.5% to 91.2%,under the same sheet resistance as 25 ?/sq.The distribution of AgNWs was optimized in this paper,and the effects of mesh shape,size,and hole area ratio on the transparent conductive properties of AgNW mesh pattern film were studied.The AgNW flexible transparent conductive films with the corresponding mesh pattern were prepared by laser etching/hot pressing transfer process.The comprehensive transparent conductive performance of the film can be effectively improved by selecting the square mesh pattern,reducing the mesh size and increasing the proportion of hole area.In addition,the AgNW mesh pattern shows better flexibility comparing with the random network film.This paper proposed a method to realize the room temperature joining of AgNW joints via electrolyte solution treatment,and expounded the mechanism of metallurgical bonding of AgNWs at room temperature.On one hand,after immersing in electrolyte solutions with certain concentration,the polyvinylpyrrolidone(PVP)on the surface of AgNWs will be eluted due to desorption.At the same time,during the film continuous wet-drying process,the capillary force accompanying the volatilization of solvent will make the AgNWs connect tighter.The combination of these two factors enhances the surface activity of AgNWs,which leads to the occurrence of atomic diffusion at the junctions.This enables AgNWs to achieve metallurgical joining at room temperature,and thereby greatly improves the film conductivity.After the electrolyte solution treatment,the sheet resistance of AgNW film decreased by 60.9%(from 67.5 ?/sq to 26.4 ?/sq),and its light transmittance(about 92.5%)remained basically unchanged.A new multilayer AgNW mesh structure was designed in this paper to prepare transparent electromagnetic shielding film with high performance.The suitable size of the AgNW mesh(with the mesh spacing of 250 ?m and the mesh line width of 50 ?m)which can improve the light transmittance of the film without producing obvious electromagnetic leakage has been obtained.Based on the mesh pattern,three-layer AgNW mesh pattern film was prepared via hot pressing in this paper,whose electromagnetic shielding effectiveness was higher than-42 d B at the frequency from 8 to 12 GHz.When the frequency was 9.5 GHz,the electromagnetic shielding effectiveness was up to-62.7 d B,and the film could still maintain the optical transmittance of 67.8% at 550 nm.The mechanism of multilayer AgNW mesh structure to enhance the transparent shielding properties was studied,the use of the mesh structure can improve the transparent conductivity of the monolayer film,and the design of the multilayer structure is beneficial to enhance the multiple reflection dissipation of electromagnetic wave.Therefore,the combination of the mesh structure and the multilayer structure can overcome the limitations of the monolayer AgNW film in improving the transparent electromagnetic shielding performance,the electromagnetic shielding performance of the film can be improved without losing the light transmittance.It provides new design ideas for the preparation of electromagnetic shielding films with both high light transmittance and high shielding effectiveness in the future.