Researchers demonstrate technique for recycling nanowires in electronics


Date:
July 27, 2021
Source:
North Carolina State University
Summary:
Researchers have demonstrated a low-cost technique for retrieving
nanowires from electronic devices that have reached the end of
their utility and then using those nanowires in new devices. The
work is a step toward more sustainable electronics.



FULL STORY ========================================================================== Researchers at North Carolina State University demonstrated a low-cost technique for retrieving nanowires from electronic devices that have
reached the end of their utility and then using those nanowires in new
devices. The work is a step toward more sustainable electronics.


========================================================================== "There is a lot of interest in recycling electronic materials because we
want to both reduce electronic waste and maximize the use we get out of
rare or costly materials," says Yuxuan Liu, first author of a paper on
the work and a Ph.D. student at NC State. "We've demonstrated an approach
that allows us to recycle nanowires, and that we think could be extended
to other nanomaterials - - including nanomaterials containing noble and rare-earth elements." "Our recycling technique differs from conventional recycling," says Yong Zhu, corresponding author of the paper and the
Andrew A. Adams Distinguished Professor of Mechanical and Aerospace
Engineering at NC State. "When you think about recycling a glass bottle,
it is completely melted down before being used to create another glass
object. In our approach, a silver nanowire network is separated from the
rest of the materials in a device. That network is then disassembled into
a collection of separate silver nanowires in solution. Those nanowires can
then be used to create a new network and incorporated into a new sensor
or other devices." The new recycling technique takes into account the
entire life cycle of a device. The first step is to design devices using polymers that are soluble in solvents that will not also dissolve the nanowires. Once a device has been used, the polymer matrix containing the silver nanowires is dissolved, leaving behind the nanowire network. The
network is then placed in a separate solvent and hit with ultrasound. This disperses the nanowires, separating them out of the network.

In a proof-of-concept demonstration, the researchers created a wearable
health sensor patch that could be used to track a patient's temperature
and hydration.

The sensor consisted of silver nanowire networks embedded in a polymer material. The researchers tested the sensors to ensure that they were
fully functional. Once used, a sensor patch is normally discarded.

But for their demonstration, the researchers dissolved the polymer in
water, removed the nanowire network, broke it down into a collection of individual nanowires, and then used those nanowires to create a brand-new wearable sensor.

While there was minor degradation in the properties of the nanowire
network after each "life cycle," the researchers found that the nanowires
could be recycled four times without harming the sensor's performance.



========================================================================== After four life cycles, you can improve the performance of the nanowire
network by introducing new silver nanowires into the mix.

"Using our approach, you get far more use from the nanowires," Zhu
says. "And even after the nanowires have broken down many times, to the
point where they can't be reused, we can still use them as feedstock
for conventional recycling.

It's a tremendous reduction in waste." One key to the recycling process
is identifying a solvent with a low surface tension for use in breaking
up the nanowire network.

"Low surface tension is important because it makes it easier for the
solvent to diffuse into the narrow junctions between nanowires in the
network, facilitating the disassembling of the network," Liu says.

The researchers found that it is also important to find the right balance
of time when breaking up the nanowire networks with ultrasound. If you
apply the ultrasound for too long, you can break the nanowires. If you
don't apply the ultrasound for long enough, you can end up with clumps
of nanowires.

"The approach we've demonstrated here could be used to recycle other nanomaterials -- such as nanoparticles, carbon nanotubes, other types
of nanowires, and two-dimensional materials -- as long as they are used
in the form of a network," Zhu says.

The work was done with support from the National Science Foundation,
under grant 1728370.

========================================================================== Story Source: Materials provided by
North_Carolina_State_University. Original written by Matt Shipman. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yuxuan Liu, Hongyu Wang, Yong Zhu. Recycling of Nanowire Percolation
Network for Sustainable Soft Electronics. Advanced Electronic
Materials, 2021; 2100588 DOI: 10.1002/aelm.202100588 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210727145234.htm

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