| The melting point of nano silver particles(Ag NPs)is lower than that of bulk silver,which can be melted and sintered at a low temperature.However,the sintered Ag NPs show the same melting point,similar conductivity and thermal conductivity with bulk silver.This process exhibits that Ag NPs have the characteristics of high serving temperature and low processing temperature,so they are widely used in the field of electronic manufacturing.At the same time,with the development of printing electronic technology and flexible electronic technology,Ag NPs ink has attracted more and more attention.At present,using high-precision printing equipments and Ag NPs ink can print precise Ag NPs coatings,but this requires a high degree of matching between nano silver ink,printing equipments and substrates.In addition,the printed Ag NPs coatings also need to optimize their conductivity and bending performance by improving sintering temperature and sintering methods.However,the applications of Ag NPs coatings in biomedical and other fields limits its sintering temperature,and even requires that Ag NPs coatings sintering at room temperature with excellent performance.Therefore,in this paper,a kind of bimodal Ag NPs ink which can match with high-precision electronic circuit printers is designed firstly.It improves the density and performance of Ag NPs coatings.On this basis,two methods to reduce the sintering temperature of Ag NPs are proposed,it realizes the sintering of Ag NPs ink on various substrates at low temperature or room temperature,and obtains nano silver ink with excellent performance Ag NPs coatings.The specific research contents are as follows:The bimodal Ag NPs ink was prepared by mixing two kinds of Ag NPs with the average particle size of 11.6nm and 52.7nm.The performance of the Ag NPs coatings after sintering was improved by complementing the two kinds of particles in the aspects of sintering kinetic force and pore filling.The average melting point of the mixed particles and the porosity of the stacking structure of the two kinds of Ag NPs were calculated theoretically.Under the condition of low porosity and low melting point,the bimodal Ag NPs with the mass ratio of small particles of 60% were determined as the solute formula of ink.In addition,the high-precision printing of Ag NPs coatings is realized by adjusting the solvent formulation of Ag NPs ink and adjusting the printing parameters corresponding to the formulation.The results showed that the porosity of the sintered structure of 60% bimodal Ag NPs coating decreased from 35.2% to 32.2% and the resistivity decreased from 4.14 ??·cm to 3.62??·cm,compared with the single size particle sintered coating.In addition,the 3D morphology of the single size particle sintered coating showed that the bimodal Ag NPs ink could alleviate the coffee ring phenomenon.After printing,the uniform structure and flat surface can be formed,and the bending service life of the coating can be prolonged.So that the maximum increase percentage of bending resistance can be reduced from 47% to 30%.In order to reduce the sintering temperature,the Ag NPs are agglomerated by sodium nitrate solution with concentration of 200 m M.The agglomeration and redispersion of Ag NPs by sodium nitrate solution or other salt solutions are used to reduce the organic coatings on the surface of Ag NPs.The results show that the Ag NPs with slow agglomeration rate are easy to be dispersed again,and the desorption of organic coatings on the surface of Ag NPs is more uniform and the effect is the most obvious in sodium nitrate solution.Comparing the heat flow curves of Ag NPs before and after the treatment,it can be seen that the sintering power of Ag NPs after the treatment is unchanged,but the initial sintering temperature is reduced from 150 ? to 120 ?.The resistivity of the coatings obtained at 120 ? after treatment is 60% lower than that before treatment,which reduces the sintering temperature.In order to reduce the sintering temperature of Ag NPs further,this paper designed to use the adsorption of hydroxyl on the surface of some oxide NPs to remove most of the organic coatings on the surface of Ag NPs,so as to realize the room temperature sintering.The hydroxyl groups on the surface of Si O2 NPs and Ti O2 NPs can make the Ag NPs in the solution agglomerate violently,and cause a large number of organic coatings on the surface of Ag NPs desorbed.Based on the above principle,oxide NPs are mixed with polyvinyl alcohol(PVA)solution to make oxide NPs coating.The above process also occured in the Ag NPs ink droplets,which makes the Ag NPs ink sintered on the coatings at room temperature.In addition,PVA makes the ink have good wettability on the surface of the coating,and makes the nano silver ink realize room temperature sintering and high-precision Ag NPs coatings on the surface of coated glass,PET and PDMS substrates without differences.Based on this method,the resistivity of Ag NPs coatings on the surface of Si O2 NPs coating and Ti O2 NPs coating at room temperature are 3.4 ??·cm and 5.5 ??·cm,respectively,which is the best result in current of room temperature sintering. |
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