Synthesis and mechanism of template-free growth of silver nanowires via syringes
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In this study, silver nanowires (Ag NWs) were synthesized in a one-pot method from silver nitrate and poly(vinyl pyrrolidone) (PVP), and reduced by ethylene glycol without the presence of chloride ion. The addition of silver nitrate and PVP was controlled by syringes. The syringe rate, and the concentrations of silver nitrate, and PVP, were manipulated to obtain Ag NWs with different widths and lengths. We have observed the phenomena of coarsening and combination of silver nanorods during the growth of the Ag NWs. With these phenomena, we have developed a growth model of Ag NWs, and successfully synthesized Ag NWs with high aspect ratios via the developed model.
I. INTRODUCTION
Nanomaterials have been the subject of enormous interest nowadays. In the past, many people focused on how to produce less-agglomerated and low-dimensional nanoparticles. Gradually, people have turned their attention to different shapes of nanomaterials, such as nanorods, nanocube, nanodisks, nanowires, and nanoplates, etc., because their properties could be tuned with the shapes.1–3 Among the nanomaterials, silver nanowires (Ag NWs) are attractive due to their high electrical and thermal conductivity, and have many applications. They can be utilized as highly transparent and flexible electrodes in polymer light-emitting diodes or polymer solar cells, and highly stretchable electrodes in muscle-like transducers.4–7 They also can be used in catalysis, chemical nano-sensors, surface-enhanced Raman scattering, infrared signature reduction, and plasmonic circuitry.8–12 The methods of producing Ag NWs can be roughly divided into two types, template-used, and template-free. The templates are cylindrical membrane pores or standing cylindrical rods within which particles are confined, such as porous anodic aluminum oxide,13 carbon nanotubes,14 and sonoself-reduction templates.15 In the templatefree method, capping agents are required to attach to the preferring face of silver to make the anisotropic growth of silver. Xia and coworkers have demonstrated a polyol process for the synthesis of Ag NWs with poly(vinyl pyrrolidone) (PVP) as a capping agent and PtCl2 as an additive.16 It was discovered that Cl ions are very helpful in the synthesis of Ag NWs, because they catch
Contributing Editor: Joan M. Redwing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.381 J. Mater. Res., Vol. 31, No. 1, Jan 14, 2016
Ag1 to form silver chloride.17 The silver chloride is a hard to dissolve salt, so it can control the concentration of Ag1 in the solution. Other anions which also form hard to dissolve silver salts are also investigated, such as S .18 For the study of capping agents, Becker used aniline, pyridine, or 3-aminopyridine as surfactants to grow Ag NWs.19 Yang used citrate as the reduction agent and capping agent to synthesize Ag NWs successfully.20 Recently, Lee’s group produced very long Ag NWs in which the longest length is about 200 lm in the presence of Cl .21 Xia and coworkers also synthesized Ag NWs
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