Highly conductive, printable and stretchable composite films of carbon nanotubes and silver

Journal name:
Nature Nanotechnology
Volume:
5,
Pages:
853–857
Year published:
DOI:
doi:10.1038/nnano.2010.232
Received
Accepted
Published online

Abstract

Conductive films that are both stretchable and flexible could have applications in electronic devices1, 2, sensors3, 4, actuators5 and speakers6. A substantial amount of research has been carried out on conductive polymer composites7, metal electrode-integrated rubber substrates8, 9, 10 and materials based on carbon nanotubes and graphene1, 2, 11, 12, 13. Here we present highly conductive, printable and stretchable hybrid composites composed of micrometre-sized silver flakes and multiwalled carbon nanotubes decorated with self-assembled silver nanoparticles. The nanotubes were used as one-dimensional, flexible and conductive scaffolds to construct effective electrical networks among the silver flakes. The nanocomposites, which included polyvinylidenefluoride copolymer, were created with a hot-rolling technique, and the maximum conductivities of the hybrid silver–nanotube composites were 5,710 S cm−1 at 0% strain and 20 S cm−1 at 140% strain, at which point the film ruptured. Three-dimensional percolation theory reveals that Poisson's ratio for the composite is a key parameter in determining how the conductivity changes upon stretching.

At a glance

Figures

  1. Schematic of the preparation of a hybrid Ag-MWNT composite film.
    Figure 1: Schematic of the preparation of a hybrid Ag–MWNT composite film.

    a, Silver nanoparticles with phenyl rings were synthesized by means of the self-assembly method. b, Multiwalled carbon nanotubes decorated with silver nanoparticles (nAg–MWNTs). c, nAg–MWNT gel was prepared by mixing and grinding nAg–MWNTs with ionic liquid (1-butyl-4-methylpyridinium tetrafluoroborate). d, nAg–MWNT gel was blended and sonicated in PVDF solution (560 W for 5 min). e, Hybrid Ag–MWNT solution was prepared by sonicating silver flakes in nAg–MWNT/PVDF solution (560 W for 10 min). The average size of the silver flakes was 3 µm. f, Hybrid Ag–MWNT composite film was finally obtained by drop casting, drying and curing.

  2. Hybrid Ag-MWNT composite films.
    Figure 2: Hybrid Ag–MWNT composite films.

    a, The cast Ag–MWNT film. Inset: magnified optical image (original magnification, ×100). b, SEM image. c, Conductivity of the hybrid Ag–MWNT film, composed of MWNTs decorated with silver nanoparticles and varying concentrations of silver flakes, investigated at 0% strain. The relative weight ratio of the self-assembled silver nanoparticles and MWNTs was fixed at 30:70 wt% (nAg:MWNTs). The conductivity of a pure silver flake film without MWNTs is also shown (purple triangle). The red line is a prediction based on a power-law relationship ( equation (1) in main text) and three-dimensional percolation theory. d, Conductivity of the hybrid Ag–MWNT film under tensile strain for five different fractions of silver flakes. Inset: cycling tests under 20% tensile strain. e, Operation of LED chips connected to the hybrid Ag–MWNT film (8.6 wt% silver flakes). The film was attached on the NBR substrate. The bottom electrodes of the LEDs were attached to the Ag–MWNT film by thermal annealing (150 °C for 1 h). The top electrodes of the LEDs were connected to gold wires. A gold wire, attached to the Ag–MWNT film by thermal annealing, was used as ground. f, Current–voltage characteristics of LED chips measured before and after stretching for different values of tensile strain (up to 30%). The current–voltage characteristics completely recovered when the strain was released in the first cycle (recovery). As a control, LED chips were attached to a gold film with silver paste and the current measured at 0% strain. g, Visual images of LEDs at an applied bias of 3.3 V before (top) and after (bottom) stretching. The LED current decreased to 71.7% at 30% strain and returned to the original value after release.

  3. Conductivity and stretchability of various hybrid Ag-MWNT films.
    Figure 3: Conductivity and stretchability of various hybrid Ag–MWNT films.

    a, Conductivity and stretchability were significantly improved when the Ag–MWNT film was perforated and embedded in NBR. b, Schematic of the hot-rolling process for the hybrid Ag–MWNT film. c, Conductivities of hot-rolled Ag–MWNT films compared with those of control materials. Filled symbols: hot-rolled Ag–MWNT films. Open symbols: triangles, diamonds, pentagons, super growth SWNT films1, 11; magenta open square, MWNT forest/polyurethane film12; green open star, textile coated with SWNT ink13; blue open circles, commercial conducting rubber1. The conductivity calculated using three-dimensional percolation theory is shown as a solid orange line in the shaded region. d, SEM image of the hot-rolled Ag–MWNT film at 50% tensile strain.

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Author information

  1. These authors contributed equally to this work

    • Kyoung-Yong Chun &
    • Youngseok Oh

Affiliations

  1. School of Mechanical Engineering, Sungkyunkwan University, Suwon, 440-746, Korea

    • Kyoung-Yong Chun,
    • Young-Jin Kim,
    • Hyouk Ryeol Choi &
    • Seunghyun Baik
  2. SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 440-746, Korea

    • Youngseok Oh,
    • Jong-Hyun Ahn,
    • Young-Jin Kim &
    • Seunghyun Baik
  3. School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon, 440-746, Korea

    • Jonghyun Rho &
    • Jong-Hyun Ahn
  4. Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Korea

    • Seunghyun Baik

Contributions

K-Y.C., Y.O. and S.B. conceived and designed the experiments, which were carried out by K-Y.C., Y.O. and J.R. H.R.C. provided nitrile butadiene rubber. Y-J.K. designed the finite element modelling, and J-H.A. designed the stretching and light-emitting diode experiments. K-Y.C., Y.O. and S.B. wrote the paper. All authors contributed to data analysis and scientific discussion.

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The authors declare no competing financial interests.

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