Synthesis and Characterization of Silver Nanowire Suspensions for Printable Conductive Media

Abstract

The purposes of this work are scaled-up synthesis of silver nanowires (AgNWs), assessment of their growth mechanism and measurement of the rheological properties of nanowire suspensions suitable for screen printing conductive circuits. A polyol synthesis process was used. The morphology and microstructure at various stages of the process were characterized by scanning electron microscopy (SEM). Aqueous silver nanowire inks with dispersant and binder were formulated. The rheological behavior of the inks was characterized by Stress Sweep Step (SSS), Steady State Flow Step (SSFS), Frequency Sweep Step (FSS) and Peak Hold Step (PHS) with a parallel plate rheometer. Rheological measurements under conditions that mimic the screen printing process have been done on the conductive inks through the PHS test to assess viscoelastic properties induced by flow alignment of the wires. Finally, the effect of silver nanowires on the rheological behavior of the ink has been compared with the effect of silver threedimensional (3D) nanoparticles (AgNPs). Since most of the available commercial silver inks suitable for screen printing process are non-aqueous solvent based, a contribution of this study is formulation of an environmentally benign water based nanowire ink. Metal one-dimensional (1D) nanostructures can play a valuable role in electronic devices, and have recently gained much attention due to their unique electrical, optical, and thermal properties. Because of the high thermal and electrical conductivity of bulk silver, it is one of the most promising metal nanowire materials.1-8 Silver nanowires hold promise as the conductive material in conductive inks suitable for screen printing. 8,[10][11][12][13][14][15] There are several methods to synthesize silver nanowires including the polyol process, hydrothermal synthesis, wet chemical process and irradiation photo reduction. Among these, the polyol process is simple and inexpensive, and provides a relatively high yield. 6 The polyol process proceeds by chemical reduction of silver ion in the presence of a polymeric surfactant. Poly(Vinyl Pyrrolidone) (PVP) acts to cap the (100) facet leading to uniaxial elongation of the initially formed silver seeds. In this process a trace amount of suitable salt can facilitate the growth of the initially formed silver seeds to the desired shape. The ethylene glycol functions as both solvent and reducing agent. [1][2][3] Various methods of printing have been used for the fabrication of printed circuits. Among these, screen printing is a rapid and inexpensive process.9 Thin printed circuits are applied in many technologies such as solar panels, flexible circuitries, and touch screens. [15][16][17][18][19][20][21][22] In screen printing, the ink is forced through a patterned screen onto a substrate. The printed pattern characteristics depend critically on the rheological properties of the ink.8 Strong shear thinning behavior permits charging of the ink at low shear onto the screen, followed by printing through the screen at high shear. Reco...

Printing Conductive Nanomaterials for Flexible and Stretchable Electronics: A Review of Materials, Processes, and Applications

“…Much attention has also been paid to synthesize AgNW inks for screen printing . The minimum feature size of 50 µm was achieved for the printed linewidth and spacing between the lines .…”

Conductive silver inks and their applications in printed and flexible electronics

“…Ag nano-wires were prepared by dissolving silver nitrate (100 mg) and PVP Similarly, Dang et. [89] synthesized Ag nano-wire suspension for printable conductive media. synthesized Ag NPs using the same polyol process [11] but changing few parameters and obtained an average diameter of 10 nm.…”

A Simple Strategy towards Highly Conductive Silver‐Nanowire Inks for Screen‐Printed Flexible Transparent Conductive Films and Wearable Energy‐Storage Devices

“…In view of possible mesh clogging, Ag NWs with length <25 µm were usually employed for formulating screen-printable Ag NW inks. [22,23] However, low film conductivity and inferior flexibility were often obtained, resulting from increased wirewire junctions and low strain endurance capacity of short Ag NWs. Here, ultralong Ag NWs with the average length of 75 µm (Figure 1b) were synthesized and first used for the formulation of high-conductive screen-printable Ag NW inks.…”

“…[12][13][14] Among them, silver nanowires (Ag NWs) have been regarded as the most promising alternative for replacing ITO, because of their good conductivity, high transparency, and especially excellent mechanical flexibility. [22,23] In general, long Ag NWs are preferred for obtaining high-conductive patterns with good flexibility. [16,17] The commonly used film deposition methods associated with the use of Ag NWs involve spin-coating, rodcoating, dip-coating, spraying techniques, etc.…”

“…[21] However, there exist many crucial challenges for making up printable Ag NW inks, such as complex formulation, environmental hazard (e.g., the use of fluorosurfactant as the binder/additive), and insufficient length of Ag NWs, which would largely limit the practical mass production and the conductivity as well as the flexibility of the resulting TCFs. [22,23] In general, long Ag NWs are preferred for obtaining high-conductive patterns with good flexibility. A high bonding strength between Ag NW patterns and flexible substrates is also critical for achieving stable photoelectric properties under mechanical deformations.…”