MSGID: 1:317/3 640177f2   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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