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The New Silver Nanowire Aerogel Preparation Technology is Lighter in Weight, Higher in Strength and
2018-07-09 17:27:42       From: Tradematt-Aerogel

In recent years, advances in metal nanowire technology have led scientists to develop new methods for the preparation of ultra-light metal foams under mild conditions, while the density is customizable and metal materials are also available. Taking an aqueous suspension solution of Cu nanowires as an example, an ultralight porous Cu aerogel can be prepared by freeze drying or critical point drying techniques.


Recently, researchers at the Lawrence National Laboratory in Lawrence, California, published a study on a new method for preparing ultra-light Ag nanowire aerogels with controlled density and pore structure. A high performance Ag foam with a density as low as 4.8 mg/cm3 was prepared for the first time. Related research results were published online last week in the journal Nano Letter. ("Ultralight Conductive Silver Nanowire Aerogels").
 
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Ultralight silver nanowire aerogel prepared by researchers
 
Previously, Lawrence Livermore National Laboratory had made many achievements in the field of ultra-light materials. This time, the researchers prepared a prototype of nanosilver by an improved polyol synthesis method and then purified by selective precipitation.

Specifically as follows: Configure about 100 ml of ethylene glycol solution containing 0.05 mM NaCl, 0.189 M PVP, about 0.0014 mM AgNO3 and 0.017 mM CuCl2, add to a round bottom flask and preheat to 185 ° C, oil bath for 1 hour; then, in vigorous 30 mL of freshly prepared AgNO3 ethylene glycol solution (0.12 M) was added dropwise with stirring; after the reaction was completed, the flask was taken out from the oil bath and cooled to room temperature to obtain silver nanowires and a small amount of silver nanoparticles.
 
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Schematic diagram of the synthesis and purification process of silver nanowires
 
Because silver nanoparticles have a negative impact on metal aerogels, the researchers purified silver nanowires by selective precipitation.

The specific method is to wash the silver nanowire solution with water, and then add acetone to the washing liquid. Since the density of the silver nanowire and the silver nanoparticle are different, the silver nanoparticle is mainly suspended in the liquid, and the silver nanowire is precipitated, and the supernatant is discarded. Liquid, the nanowire is enriched and purified by redispersing the precipitate in water.
 
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Comparison of purified and unpurified silver nanowires

The prepared silver nanowires can be used as a component for preparing a conductive silver aerogel. The researchers formed a vortex of a known concentration of silver nanowire suspension in a glass vial and immediately placed it on a metal block previously cooled with liquid nitrogen; due to the vertical temperature gradient, the ice crystals nucleated from the bottom and gradually Growing up, as the ice crystals increase, the silver nanowires are redistributed by the aligned ice layers; the frozen silver nanowire suspension is freeze-dried and heat treated to remove PVP, resulting in a highly porous silver nanowire aerogel. .

Due to this unique preparation method, the silver aerogel has a unique layered porous structure. By adjusting the concentration of the silver nanowire suspension, the researchers can control the density of the aerogel to a minimum of 4.8 mg/cm3. In addition, other shapes of aerogels such as discs, spheres and hemispheres can be prepared through specially designed molds.
 
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Schematic diagram of the preparation process of silver nanowire aerogel
 
The researchers tested the performance of this silver nanowire aerogel and found that its conductivity is 51000 s / m. The mechanical properties of the silver nanowire aerogel showed a "elastic strengthening" behavior with a Young's modulus of up to 16,800 Pa.

"Interestingly, the experimental results show that the deformation mechanism of the Ag nanowire aerogel we prepared is different from that of the conventionally prepared metal foam, which is the deformation caused by bending, which means that it has more than other foams or aerogels. Higher structural strength, which is another hidden advantage of it.” The researchers said: “As for its performance so good, this has yet to be further modeled to reveal.”

Source: Nano Letter