In situ monitoring of the electrical property of carbon nanotube thin film in floating catalyst chemical vapor deposition

In floating catalyst chemical vapor deposition (FCCVD), when a carbon nanotube (CNT) network film is produced by filter collection, the film thickness is adjusted by controlling the collection time. However, even with consistent synthesis parameters, the synthesis condition in FCCVD changes constantly depending on the carbon and catalyst adhesion to the inner wall of the reaction tube. Thus, the rate of synthesis changes, making it difficult to obtain the target film thickness repeatedly and stably. We propose a method of monitoring CNT film thickness and percolation threshold by the in situ measurement of the electrical impedance during the deposition. The time evolution of the measured impedance is reproducible by an equivalent electrical circuit simulation.

A Novel Oriented CNT fiber/PDMS Elastic Conductive Composite with Reversible Two-stage Conductivity

In recent years, intensive researches have been stimulated to explore the promising prospect for carbon nanotubes (CNTs) in the fabrication of novel polymer sensor composites. In this study, the fabrication and properties of a flexible and stretchable composite elastomer fabricated from direct-spun carbon nanotube fiber (yarns) were presented, and the novel CNT fiber/polydimethylsiloxane (PDMS) elastic conductive composite shows the reversible two-stage conductivity owing to its unique structure of CNTs fabricated by the floating catalyst chemical vapor deposition (FCCVD). As the strain increased from 0% to 10% (Stage I), stretching the oriented CNT fiber/PDMS elastic conductive composite induces a constant decrease in the conductive pathways and contact areas between CNTs depending on the stretching distance. However, this composite elastomer will retain almost stable electrical resistance while being stretched by over 10% (Stage II). Furthermore, the composite shows very little variation in resistance under 187 stretching–releasing cycles up to a pre-strain level of 6%, indicating the outstanding stability and repeatability in performance as stretchable conductors. The microstructure, reversible two-stage conductive properties and mechanism were also discussed.

Catalyst-Mediated Enhancement of Carbon Nanotube Textiles by Laser Irradiation: Nanoparticle Sweating and Bundle Alignment

The photonic post-processing of suspended carbon nanotube (CNT) ribbons made by floating catalyst chemical vapor deposition (FC-CVD) results in selective sorting of the carbon nanotubes present. Defective, thermally non-conductive or unconnected CNTs are burned away, in some cases leaving behind a highly crystalline (as indicated by the Raman G:D ratio), highly conductive network. However, the improvement in crystallinity does not always occur but is dependent on sample composition. Here, we report on fundamental features, which are observed for all samples. Pulse irradiation (not only by laser but also white light camera flashes, as well as thermal processes such as Joule heating) lead to (1) the sweating-out of catalyst nanoparticles resulting in molten catalyst beads of up to several hundreds of nanometres in diameter on the textile surface and (2) a significant improvement in CNT bundle alignment. The behavior of the catalyst beads is material dependent. Here, we show the underlying mechanisms of the photonic post-treatment by modelling the macro- and microstructural changes of the CNT network and show that it is mainly the amount of residual catalyst which determines how much energy these materials can withstand before their complete decomposition.