Silver
Silver is a soft, white, lustrous transition metal having the highest electrical conductivity (6.3 × 107 S/m) among all the metals and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals and in minerals such as argentite and chlorargyrite.
Silver nanowires
Silver nanowires have been attracting more and more attention because of their intriguing electrical, thermal, and optical properties. Silver has the highest electrical conductivity among all the metals, by virtue of which Ag NWs are considered as very promising candidates in flexible electronics.
Production of silver nanowires
To produce an aqueous dispersion of metallic nanowires, a silver nanowire-polyol dispersion is obtained through a polyol method and is then subjected to centrifugal separation and subsequent solvent replacement. Silver nanowires are synthesized using an aqueous solvent which utilizes ammonia silver in an autoclave at 120° C. for 8 hours. The presence of various ions has been shown to have a strong impact on the shape and size of silver nanostructures produced via the polyol reduction of AgNO3. Silver nanowires having both transparency and conductivity are produced in an aqueous solvent at a temperature equal to or below the boiling point of the solvent, and an aqueous dispersion containing the silver nanowires, the dispersion being excellent in storage stability after coating and dispersion stability. For example, silver nanowires produced is through immersing a glass substrate on which cupper fine particles are formed by an electric deposition into an aqueous solution of silver nitrate overnight.
Rapid synthesis
A simple and rapid (within one hour) route to Ag nanowires is reported in the literature. In this method ethylene glycol serves as the solvent and a precursor to the reducing agent. The reaction could be performed in disposable glass vials, with all the reagents being delivered using pipettes. In addition to the use of poly(vinyl pyrrolidone) as a stabilizer, copper (I) or copper (II) chloride had to be added to the reaction to reduce the amount of free Ag+ during the formation of initial seeds and scavenge adsorbed oxygen from the surface of the seeds once formed. In doing so, Ag nanowires are grown preferentially.
Soft solution method
Many non-chemical methods for fabricating nanowires have been developed having obvious advantages over preparation of peculiar morphological silver nanowires, but they are usually complicated, highly energy-consuming and sophisticated. Therefore, the chemical method has been the most promising way for the large-scale fabrication of silver nanowires in future. Among the various routes, the soft solution method is now the hottest point in the field of silver nanowires at present.
Template method
Photoinitiated growth of silver nanowires within a chemically active organic nanotubular template is reported in the literature. Self-assembled supramolecular nanotubes of J-aggregated amphiphilic cyanine dye in aqueous solution are employed as chemically active templates for the photoinitiated formation of silver nanowires. The template has a small and well-defined diameter; photochemically active, allows photoinitiation of the structure formation and capable of processing in aqueous solution. The template can be removed after the reaction, or made to functionalize it further, e.g. with optoelectronically active polycations, providing access to quasi one-dimensional hybrid structures with well-defined metallic nanowires as a core.
Electroless deposition
Single crystal silver nanowires can be fabricated based on the electroless deposition of silver into the pores of the polycarbonate membranes by the metal amplification process. Researchers report that a gold film on one side of the nanoporous membrane is used as the initiation layer for the silver crystal growth, while the pores of the membrane are used for guiding the growth of the silver crystal into a cylindrical nanostructure. Researchers claim that the metal amplification technique presents an electroless, simple, and inexpensive solution to the challenge of fabricating silver nanowires for electronic, optical, and biological applications.
Vacuum filtration
Ag NW films have been fabricated using techniques, such as vacuum filtration, transfer printing onto poly(ethylene terephthalate) (PET) substrates, drop casting and air-spraying from NW suspension. The film obtained from air-spraying coating is much better, but still forms sparse and non-uniform networks.
Applications
Silver nanomaterials have almost unlimited applications.
Optical
Solar (thin film, crystalline silicon)
Medical imaging
Raman spectroscopy
Optical limiters
Surface plasmons
Conductive
High-intensity LEDs
Touchscreen displays
Computer boards
Conductive adhesives
LCDs
Sensors
Anti-microbial
Bandages
FilmsAir & water purification
Sterile equipment
Food preservation
Clothing
Chemical & Thermal
Catalysts
Sensors
Pastes
Chemical vapor
Sensors
Polymers
Thermal adhesives