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

Thurid S Gspann,Fiona R Smail,James A Elliott,Jennifer Mizen,Philipp A Kloza,John D Cook,Wei Tan,Jeronimo Terrones,Daniel Tune,Adarsh Kaniyoor,John S Bulmer,Giorgio Divitini

doi:10.3390/catal11030368

Abstract

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.

Highlights

In contrast to [10], where the laser beam was scanned over entire samples, here, in order to isolate effects of a sustained laser heating, we concentrate on single point irradiation experiments where the laser pulses are fixed on one location on the carbon nanotube (CNT) sample
Apart from the catalyst particle sweating, for all samples we observe a significant increase in bundle alignment
By adjusting the carrier gas flow, the ratio of precursors and their dilution, and thermal conditions during synthesis, the aerogel can be tailor-made regarding the CNT’s number of walls, bundle length, entanglement and alignment, and the amount of co-synthesized coating and ferrous impurities anchored in the network

Summary

Introduction

The spinning process works due to the entanglement of the CNT bundles inside the reactor. This entanglement gives the CNT network its mechanical strength and integrity, allowing for higher tensile forces to be applied during extraction of aerogel, but may impair its electrical or thermal conductivity [2,3,4] compared to an ideal, perfectly aligned assembly of nanotubes. Any co-synthesized bundle coating, depending on its nature and amount, may affect the physical properties of the nanotube textile [3]. Several publications have discussed the advantages of CNT bundle alignment for mechanical, electrical, and thermal properties of CNT films or fibres [5,6,7,8,9]. Many research efforts have focused on increasing CNT alignment without jeopardizing the as-produced mechanical integrity of the textiles

Methods

Results

Conclusion