Researchers propose a simple, inexpensive approach to fabricating carbon nanotube wiring on plastic films

Date:
March 2, 2023
Source:
Tokyo University of Science
Summary:
Researchers have developed an inexpensive method for fabricating
multi- walled carbon nanotubes (MWNTs) on a plastic film. The
proposed method is simple, can be applied under ambient conditions,
reuses MWNTs, and produces flexible wires of tunable resistances
without requiring additional steps. It eliminates several drawbacks
of current fabrication methods, making it useful for large-scale
manufacturing of carbon wiring for flexible all-carbon devices.


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FULL STORY ========================================================================== Researchers from Tokyo University of Science in Japan have developed an inexpensive method for fabricating multi-walled carbon nanotubes (MWNTs)
on a plastic film. The proposed method is simple, can be applied under
ambient conditions, reuses MWNTs, and produces flexible wires of tunable resistances without requiring additional steps. It eliminates several
drawbacks of current fabrication methods, making it useful for large-scale manufacturing of carbon wiring for flexible all-carbon devices.


========================================================================== Carbon nanotubes (CNTs) are cylindrical tube-like structures made
of carbon atoms that display highly desirable physical properties
like high strength, low weight, and excellent thermal and electrical conductivities. This makes them ideal materials for various applications, including reinforcement materials, energy storage and conversion
devices, and electronics. Despite such immense potential, however,
there have been challenges in commercializing CNTs, such as their
incorporation on plastic substrates for fabricating flexible CNT-based
devices. Traditional fabrication methods require carefully controlled environments such as high temperatures and a clean room. Further, they
require repeat transfers to produce CNTs with different resistance values.

More direct methods such as laser-induced forward transfer (LIFT) and
thermal fusion (TF) have been developed as alternatives. In the LIFT
method, a laser is used to directly transfer CNTs onto substrates, while
in TF, CNTs are mixed with polymers that are then selectively removed
by a laser to form CNT wires with varying resistance values. However,
both these methods are expensive and have their unique problems. LIFT
requires expensive pulsed lasers and preparation of CNTs with specific resistance values, while TF uses large amounts of CNTs that are not
utilized and go to waste.

Aiming to develop a more simple and inexpensive approach, Associate
Professor Dr. Takashi Ikuno along with his collaborators, Mr. Hiroaki
Komatsu, Mr. Yosuke Sugita and Mr. Takahiro Matsunami at Tokyo
University of Science, Japan, recently proposed a novel method that
enables fabrication of multi-walled CNT (MWNT) wiring on a plastic film
under ambient conditions (room temperature and atmospheric pressure)
using a low-cost laser.

The breakthrough, published in the journal Scientific Reports on 08
February 2023, involves coating a polypropylene (PP) film with an MWNT
film about 10 mm thick and then exposing it to a mW UV laser. The result
is a conductive wiring made of a combination of MWNT and PP.

"This process enables the easy 'drawing' of wiring and flexible devices
for wearable sensors without the need for complex processes," highlights
Dr. Ikuno.

The researchers attributed the formation of these wires to the difference
in the thermal conductivities between the MWNT and the PP film. As the
MWNT/PP film is exposed to the laser, the high thermal conductivity
of the MWNT layer causes the heat to spread along the length of the
wire, resulting in high temperatures at the MWNT-PP interface and lower temperatures elsewhere in the PP film. Directly below the laser, where temperatures are the highest, the PP diffuses into the MWNT film to form
a thick PP/MWNT composite, while a thin PP/ MWNT layer is formed at the
edges of the laser where temperatures are relatively low.

The proposed method also allows the fabrication of carbon wires with
different resistance values within the same process (without repeat
transfer) by simply changing the irradiation conditions, thereby
eliminating the need for additional steps. Exposing the PP/MWNT film
to high laser energies, achieved either by low scanning speeds, a high
number of laser exposures, or the use of a high-powered laser, produces
thicker wires with a higher concentration of MWNTs. Consequently, the
lower resistivity of MWNT and the thicker wire lowers the resistance
per unit length of the wire (resistance is directly proportional to the
ratio between the resistivity and the thickness of the wire).

By precisely controlling the exposure of the MWNT/PP film to laser
light, the researchers successfully fabricated MWNT wires with a wide
range of resistance values, from 0.789 kO/cm to 114 kO/cm. Moreover,
these wires were highly flexible and maintained their resistance even
when bent repeatedly.

Additionally, the method solved one of the pressing issues with current techniques, namely the inability of LIFT and TF techniques to reuse
CNTs not utilized in the fabrication process. In the proposed method,
MWNTs not incorporated into the PP film during laser irradiation can be recovered and reused, allowing for the creation of new MWNT wires with
little to no change in resistance values.

With its simplicity, efficient utilization of CNTs, and the capability
to create high-quality wires, the new method has the potential to realize large- scale manufacturing of flexible carbon wiring for flexible sensors
and energy conversion and storage devices.

"We expect the process cost to be significantly reduced compared to
that for conventional methods. This, in turn, will contribute to the realization of low- cost flexible sensors that are expected to have wide applications in large quantities," concludes Dr. Ikuno.

* RELATED_TOPICS
o Matter_&_Energy
# Optics # Electronics # Graphene # Detectors #
Wearable_Technology # Thermodynamics # Chemistry # Physics
* RELATED_TERMS
o Carbon_nanotube o Carbon-14 o Hydrocarbon o Carbon_dioxide
o Carbon_monoxide o Silicon o Fullerene o Radiocarbon_dating

========================================================================== Story Source: Materials provided by Tokyo_University_of_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Hiroaki Komatsu, Takahiro Matsunami, Yosuke Sugita, Takashi
Ikuno. Direct
formation of carbon nanotube wiring with controlled electrical
resistance on plastic films. Scientific Reports, 2023; 13 (1) DOI:
10.1038/s41598- 023-29578-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/03/230302093402.htm

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