Controllable Preparation And Properties Of Silver Nanowires

In recent years,silver nanowire(AgNWs)has received more and more attention owing to their potential applications in organic solar cells,flexible touch screens and organic lightemitting diodes.therefore it.However,there are some issues regarding poor reproducibility,tedious process and uncontrollable size,which seriously limit its large-scale production and wide application.Microfluidic has the characteristics of faster mass transfer and heat transfer,and better solution mixing,which provides a new technology for the preparation of high quality AgNWs.In this thesis,AgNWs with controlled size were synthesized by polyol method with the aid of microfluidic technology.The effects of different experimental parameters on the morphology,diameter,aspect ratio and optical absorption of AgNWs were studied in ethylene glycol phase and propylene glycol phase system,respectively.The main research contents are as follows:AgNWs were respectively synthesized by continuous flow in microreactor and traditional batch method.AgNWs with the average diameter of 60 nm and the average length of 15 ?m could be obtained within 30 min without the protection of nitrogen.In this case,only a small amount of Ag by-products could be observed.In comparison,Low-yield AgNWs with average diameter of 60 nm and average length of 4 ?m were produced by traditional batch method under the protection of nitrogen for 1 h.The experimental results show that long length AgNWs prepared by continuous flow method is attributed to better mixing of precursors and diffusioncontrolled process.This method is not only simple and easy to operate,but also improves the controllability and repeatability of AgNWs.Ethylene glycol(EG)was used as polyol to synthesize AgNWs at different Na Cl concentration,PVP concentration and molecular weight in a continuous flow reactor.With the decrease of Na Cl concentration,the yield of AgNWs increases along with the disappearance of Ag Cl nanocubes.With the increase of the molar ratio of PVP to silver nitrate,thinner and longer AgNWs with less by-products could be obtained because of better passivation of(100)plane on Ag seeds and AgNWs.When the existence of a small amount of short-chain PVP(PVP-55K)together with long-chain PVP(PVP-1.3M),AgNWs with diameter 40 nm and high aspect ratio up to 2500 can be formed within 30 min due to the fully passivation of(100)plane.Combined with TEM analysis,the formation mechanism of high-aspect ratio AgNWs is mainly due to sizedistribution focusing growth of Ag seeds and oriented attachment bewtten Ag nanorods..When propylene glycol(PG)was used as polyol,AgNWs were prepared in a continuous flow reactor by changing reaction temperature,reaction time,tube length of microreactor,concentration of benzoin reductant and mixture ratio of EG to PG.It is found that reaction temperature can be reduced to 140 ? when PG is used alone because of its higher reducibility thus producing thinner AgNWs with shorter average length 11 ?m.By Changing the tube length and introducing different concentrations of benzoin will lead to the increase of the diameter of AgNWs along with shorter length and higher by-products.The appearance of EG has a significant effect on the wire length and diameter.As the mixing volume ratio of PG/EG increases from 1:0 to 3:7,the wire length increases to 70 ?m and the diameter increases to 65 nm at the same time.When the mixing ratio is 5:5,the aspectratio of AgNWs could reach 1300 with small amounts of by-product.The results demonstrate that high reducibility of the solvent leads to the uncontrollable formation process of Ag seeds and the growth process of AgNWs,which is not conducive to the synthesis of high aspect ratio AgNWs.