Many efforts have been devoted to increasing the conductivity of CNT TCFs made with the floating catalyst chemical vapor deposition (FCCVD). However, intrinsic nanotube collisions in the aerosol process of FCCVD lead to a tread-off between yield and performance, because bundling increases when increasing the yield i.e. production rate, with the bundling reducing the growth rate as well as increasing sheet resistance at the given film transmittance. Here, we report TCFs of large-diameter CNTs from methane-based FCCVD overcoming the performance-yield tradeoff. Based on the Fe-C-S system, the double-wall CNTs (DWCNTs) with a mean diameter of 4.15 nm and a mean bundle length of 20 um have been synthesized via FCCVD and directly deposited to form TCFs. After gold chloride solution doping, the TCFs have an excellent performance of 42 ohm/sq sheet resistance at 90 % transmittance. Unexpectedly, these high-performance DWCNTs films have an ultra-high yield i.e. production rate, being two orders of magnitude higher than that of SWCNT based TCFs with similar performance. Especially, these high-yield DWCNTs films contain small bundles with around 50 % of CNTs being individual, which is completely different from other FCCVD results for SWCNTs produced at much lower yield. Moreover, the large-diameter DWCNTs seem to flatten at the junctions, which may provide a larger contact area between the tubes and accordingly reduce the contact resistance. These unique features of large-diameter CNTs in small bundles offer the route to obtain high-performance CNT TCFs with high yield. These results imply a new model with optimization windows for high-performance CNT TCFs with high yields and accordingly at reduced cost, and may accelerate the practical application of CNTs TCFs.
Professor Esko I. Kauppinen, PhD (Physics) is the Vice-Dean responsible for research, innovations and industry relationships at the Aalto University School of Science and Tenured Professor of Physics at the Department of Applied Physics. He has published more than 443 scientific journal papers e.g. in Nature Nanotechnology, NanoLetters, ACS Nano, Angewandte Chemie, Carbon, Energy and Environmental Sciences etc., having Hirsch-index over 52 and over 10 600 citations. He has given more than 120 keynote and invited conference talks and 220 talks at world leading companies and universities. He is considered one of the world leading authors in the area of single walled carbon nanotube synthesis, characterisation and thin film applications as well as in the gas phase synthesis of particles for inhalation drug delivery. He is the founding member of the companies Canatu Oy (http://www.canatu.com) and Teicos Pharma Oy (www.teicospharma.com).
Characterization of the distribution of multilayer carbon nanotubes in polymer composites using cyclic measurements of current-voltage characteristics
S. I. Moseenkov1, A. V. Zavorin1,2, and V. L. Kuznetsov1,2
1 Boreskov Institute of Catalysis SB RAS, Lavrentiev ave. 5, 630090 Novosibirsk, Russia
2 Novosibirsk State University, Pirogova str. 2, 630090 Novosibirsk, Russia
kuznet@catalysis.ru
In this paper we suggested a method for evaluating the uniformity of the nanotube distribution in the MWCNT-polymer composites based on sequential measurements of their current-voltage-conductivity (СVС) characteristics in a wide range of applied voltages (E, up to 103 V/mm). The MWCNTs in the composites form ohmic contacts (direct contacts between the nanotubes) and non-ohmic contacts (nanotubes in the contact are separated by several polymer chains). In our study we investigated composites with polyethylene and poly(methyl methacrylate) matrixes produced using MWCNTs with different aspect ratio (AR, 36 to 3000). In composites with uniform distribution of nanotubes (near the percolation threshold), large number of non-ohmic contacts results in high specific resistivity to 1013-1014 Ωcm. This makes it difficult to measure the resistance at low E and impairs reproducibility of the results because partial transformation of contacts due to the heat release under electrical current takes place during the measurements already at E = 0.3 V/mm and current density 410-8 A/cm2. Furthermore, in the case of a high applied voltage, the decrease in resistance can reach 105 due to the formation of new ohmic contacts between nanotubes. The number of ohmic contacts in the composites also increases when the conductivity and IV characteristics are measured due to irreversible transformation of non-ohmic contacts into ohmic contacts under the action of electrical thermal breakdown. This effect increases together with the number of non-ohmic contacts in the composite, which was demonstrated for composites modified by MWCNTs with AR values ranging from 36 to 3000. Therefore, the MWCNT percolation threshold largely depends on measurement conditions and on the sample's "history". We demonstrated that cyclic IV measurements can be used to characterize the nature of the contacts between the nanotubes in polymer composites, in particular, to determine the presence of non-ohmic and ohmic contacts, transformations of the former into the latter, and to control the conductivity of MWCNT based composites using electric fields with a strength higher than 1 V/mm.
The suggested method for activation of isolated contacts between nanotubes can be used for controlled modification of MWCNT based composites for production of functional materials or devices on their basis (e.g. pressure sensors or deformation sensors, etc.) [1,2].
Acknowledgments. The work was carried out within the framework of the RFBR project No. 20-33-70120.
References:
[1] Moseenkov S.I., et al., Journal of Structural Chemistry. 2020. V.61. N4. P. 628639.
[2] Moseenkov S.I., et al., eXPRESS Polymer Letters. 2019. V.13. N12. P. 10571070.
The electric resistivity and piezoresistive response of functional carbon nanocomposites
Hassaan A. Butt, Stepan V. Lomov, Iskander S. Akhatov, Sergey G. Abaimov
Centre for Design, Manufacturing and Materials
Skolkovo Institute of Science and Technology, Moscow, Russia
hassaan.butt@skoltech.ru
Functional nanocomposites are allowing fundamental changes to the way system and material monitoring and testing takes place, both during manufacturing as well as during composite usage lifecycle [1, 2]. One such application of these materials is the replacing of traditional sensors for deformation sensing, allowing the reduction in cost and weight of systems and potential usage has already been highlighted in fields such as the automotive, aerospace, renewable energy and sensor manufacturing sectors [3, 4].
In recent years, nano-carbon particles, in particular, carbon nanotubes and graphene/derivatives, have been under intense scientific scrutiny as additives for composite manufacturing, not only increasing the mechanical properties of composites but allowing the final composites to be electrically conductive and piezoresistive in nature [5, 6].
In this work, industrial masterbatches have been used to manufacture functional nanocomposites and evaluate their feasibility for large scale production of strain sensing thermoplastic nanocomposites. Masterbatches are high weight/volume fraction compounds premixed with nanoadditives in a selected matrix and provide a safe medium for implementing nanomaterials on an industrial scale. From a safety, production line modification and financial standpoint, masterbatches are the most feasible implementation medium for large scale production. However, very few publications deal masterbatch-based nanocomposites and of those available, even fewer deal with piezoresistivity or self-diagnostics.