Research ArticleMATERIALS SCIENCE

Super-elasticity of three-dimensionally cross-linked graphene materials all the way to deep cryogenic temperatures

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Science Advances  12 Apr 2019:
Vol. 5, no. 4, eaav2589
DOI: 10.1126/sciadv.aav2589
  • Fig. 1 The structure of the 3DGraphene foam.

    (A) Schematic of the formation and structure of the bulk 3DGraphene foam. The spatial density of oxygen atoms mainly at the edges in the schematic was adjusted for clarity but did not represent its actual ratio in the material. (B) Cross-sectional scanning electron microscopy (SEM) image of the 3DGraphene foam (along the axial direction) with a homogeneous and highly porous structure. (C) Magnified SEM of the 3DGraphene foam. Inset: Magnification of the selected area that demonstrates that graphene sheets are chemically cross-linked together at the cell node (with quasi-hexagonal configuration). Scale bars, 200 μm (B), 50 μm (C), and 10 μm [inset of (C)].

  • Fig. 2 Mechanical properties of the 3DGraphene foam at cryogenic temperature of 4 K.

    (A) Schematic of measurement and optical images demonstrating reversible super-compressive elasticity of the 3DGraphene foam at 4 K. Dotted boxes mark the cylindrical sample with both 15 mm diameter and height; yellow and green arrows indicate the moving directions of the test head. The brightness and contrast of the optical images are enhanced for clarity. Scale bars, 1 cm. (B) The single-cycle stress-strain curve at 4 K is almost completely the same with the curve at RT (both along the axial direction at a rate of 0.1% strain s−1). (C) Strain versus time curve of a stepwise compress-release measurement with increasing maximum strains but a constant rate (0.1 strain s−1) and the corresponding stress-strain curves of such measurements at 4 K along both axial and radial directions. (D) Young’s modulus and Poisson’s ratio plots versus applied engineering strain (and the relative density of the compressed 3DGraphene foam) at 4 and 298 K, showing almost identical Young’s modulus variation trend and constantly near-zero Poisson’s ratio. (E) Stress-time curves of 100 compress-release cycles along the axial direction at 4 and 298 K. Each 2-s cycle was performed between 0 and 90% strain at a rate of 90% strain s−1, as shown in the inset. The stress values at 0 and 90% strains of each cycle were emphasized by labeling symbols, and the dashed and dotted lines correspond to least-squares fittings of stress at 0 and 90% strains of each temperature, respectively. Almost identical and overlapping stress-time curves indicate the great cycle stability of the material maintained even at cryogenic temperature. (F and G) The Young’s moduli (F) and near-zero Poisson’s ratios (G) both remain unchanged during the cycling test at 4 and 298 K, showing the great cycle stability down to deep cryogenic temperatures. Error bars in (D), (F), and (G) represent SDs for repeated measurements.

  • Fig. 3 In situ SEM observations of reversible compressive elasticity of the 3DGraphene foam at 4 K.

    (A and B) Totally reversible deformation of the microstructure for the first (A) and ninth (B) compress-release cycles. (C and D) Magnifications of the marked zones with increasing compressive strains, demonstrating deformations of the graphene sheets during compression. (E and F) Overlaps of marked zone 1 with 0% strain in the first and ninth compress-release cycles (E) and of marked zone 2 with 77.9% strains in the first and ninth compress-release cycles (F), and the images of the first and ninth cycles are digitally processed with green and red colors, respectively. Scale bars, 100 μm (A and B), 10 μm (C and D), and 20 μm (E and F).

  • Fig. 4 Temperature invariance of the mechanical properties of the 3DGraphene foam.

    (A and B) 3D surface graphs of the stress dependence on strain and temperature in the compression (A) and release (B) processes of the 3DGraphene foam, both exhibiting clear temperature invariance from 4 to 1273 K. (C and D) Grouped column graph (C) of Young’s modulus and intensity map graph of Poisson’s ratios (D) at a series of engineering strains measured at different temperatures, showing excellent temperature invariance of both Young’s modulus and near-zero Poisson’s ratio. Error bars represent SDs for the repeated measurements.

  • Fig. 5 Simulation of the mechanical properties of the 3DGraphene foam in a wide temperature range down to the cryogenic region.

    (A) Overlays of the in situ SEM images for the full compress-release cycles of the same sample at 4 and 1273 K and enlargements for the labeled areas, showing that the structural stability and the reversible deformations of graphene sheets at microscopic scale are wide temperature independent. Green and red arrows mark the same graphene sheets at 4 and 1273 K. Scale bars, 100 μm (top row) and 25 μm (bottom row). (B and C) The theoretically simulated stress-strain curves agree well with the experimental results for the compression process of the 3DGraphene foam at 4 K (B) and 1273 K (C) and also with the well-matched simulated Young’s modulus–engineering strain curves for 4 K [inset of (B)] and 1273 K [inset of (C)]. (D and E) Theoretically simulated temperature dependence curves of stress (D) and Young’s modulus (E) fit well with the experimental data, suggesting almost negligible temperature influence on the stress-strain behavior and Young’s modulus in the compression process of the 3DGraphene foam down to cryogenic temperatures. All error bars represent SDs for the repeated measurements.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/4/eaav2589/DC1

    Supplementary Methods

    Supplementary Discussion

    Fig. S1. The schematic of the sample platform with precise positioner and temperature control in the SEM for in situ and variable-temperature characterization.

    Fig. S2. Schematic of the homemade apparatus for mechanical property measurement from 4 to 1273 K.

    Fig. S3. Measurements of the Young’s modulus of the 3DGraphene foam at 4 K.

    Fig. S4. Measurements of the Poisson’s ratio of the 3DGraphene foam at 4 K.

    Fig. S5. The schematic of the nodes under compression.

    Fig. S6. The modeling architecture of the plane perpendicular to the compression direction.

    Fig. S7. Schematic of the proposed elastic deformation of the 3DGraphene foam under compressive stress.

    Fig. S8. The schematic of the periodic honeycomb-like cell architecture for modeling the 3DGraphene foam and enlargement of one unit cell under the applied compressive stress.

    Fig. S9. The schematic of a cell node under the applied compressive stress.

    Fig. S10. The schematic of elastic bending of the graphene cell wall under the applied compressive stress.

    Fig. S11. The schematic of elastic buckling of the graphene cell wall under the applied compressive stress.

    Fig. S12. The schematic of deeply elastic bending of the graphene cell wall at large strain of the sample.

    Fig. S13. The photograph of the 3DGraphene foam samples.

    Fig. S14. Cross-sectional SEM images of the 3DGraphene foam.

    Fig. S15. Energy dissipation mechanism.

    Fig. S16. Young’s modulus–engineering strain plots along the axial and radial directions at different temperatures.

    Fig. S17. Poisson’s ratio at different engineering strain of the 3DGraphene foam along the axial and radial directions at different temperatures.

    Fig. S18. In situ SEM observations of the 3DGraphene foam during compress-release cycles at 4 K.

    Fig. S19. The Young’s modulus versus applied engineering strain at different temperatures.

    Fig. S20. The Poisson’s ratio versus applied engineering strain at different temperatures.

    Fig. S21. The cyclic stability at different temperatures.

    Fig. S22. The stepwise compress-release cycles with increasing maximum strain along both the axial and radial directions at different temperatures.

    Fig. S23. Comparison of the in situ SEM images of the same sample under 0, 45, and 90% strains in the compress process.

    Fig. S24. Thermal expansion of the 3DGraphene foam in both axial and radial directions.

    Fig. S25. A typical AFM image of GO sheets.

    Fig. S26. The simulated stress-strain curve at 298 K.

    Fig. S27. The simulated Young’s modulus–engineering strain curves at different temperatures.

    Fig. S28. The simulated tangent modulus–strain curves at different temperatures.

    Fig. S29. Results of cyclic mechanical test at 1273 K and that of the following test at other temperatures for the same samples.

    Fig. S30. The relationship between compressed density and Young’s modulus with strain.

    Movie S1. In situ optical observation for compress-release cycles of the 3DGraphene foam at 4 K and corresponding stress-strain transient curves.

    Movie S2. In situ optical observation for compress-release cycles of the 3DGraphene foam at 1273 K and corresponding stress-strain transient curves.

    Movie S3. In situ SEM observation for compress-release cycles of the 3DGraphene foam at 4 K.

    Movie S4. In situ SEM observation for compress-release cycles of the 3DGraphene foam at 1273 K.

    References (6080)

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Methods
    • Supplementary Discussion
    • Fig. S1. The schematic of the sample platform with precise positioner and temperature control in the SEM for in situ and variable-temperature characterization.
    • Fig. S2. Schematic of the homemade apparatus for mechanical property measurement from 4 to 1273 K.
    • Fig. S3. Measurements of the Young’s modulus of the 3DGraphene foam at 4 K.
    • Fig. S4. Measurements of the Poisson’s ratio of the 3DGraphene foam at 4 K.
    • Fig. S5. The schematic of the nodes under compression.
    • Fig. S6. The modeling architecture of the plane perpendicular to the compression direction.
    • Fig. S7. Schematic of the proposed elastic deformation of the 3DGraphene foam under compressive stress.
    • Fig. S8. The schematic of the periodic honeycomb-like cell architecture for modeling the 3DGraphene foam and enlargement of one unit cell under the applied compressive stress.
    • Fig. S9. The schematic of a cell node under the applied compressive stress.
    • Fig. S10. The schematic of elastic bending of the graphene cell wall under the applied compressive stress.
    • Fig. S11. The schematic of elastic buckling of the graphene cell wall under the applied compressive stress.
    • Fig. S12. The schematic of deeply elastic bending of the graphene cell wall at large strain of the sample.
    • Fig. S13. The photograph of the 3DGraphene foam samples.
    • Fig. S14. Cross-sectional SEM images of the 3DGraphene foam.
    • Fig. S15. Energy dissipation mechanism.
    • Fig. S16. Young’s modulus–engineering strain plots along the axial and radial directions at different temperatures.
    • Fig. S17. Poisson’s ratio at different engineering strain of the 3DGraphene foam along the axial and radial directions at different temperatures.
    • Fig. S18. In situ SEM observations of the 3DGraphene foam during compress-release cycles at 4 K.
    • Fig. S19. The Young’s modulus versus applied engineering strain at different temperatures.
    • Fig. S20. The Poisson’s ratio versus applied engineering strain at different temperatures.
    • Fig. S21. The cyclic stability at different temperatures.
    • Fig. S22. The stepwise compress-release cycles with increasing maximum strain along both the axial and radial directions at different temperatures.
    • Fig. S23. Comparison of the in situ SEM images of the same sample under 0, 45, and 90% strains in the compress process.
    • Fig. S24. Thermal expansion of the 3DGraphene foam in both axial and radial directions.
    • Fig. S25. A typical AFM image of GO sheets.
    • Fig. S26. The simulated stress-strain curve at 298 K.
    • Fig. S27. The simulated Young’s modulus–engineering strain curves at different temperatures.
    • Fig. S28. The simulated tangent modulus–strain curves at different temperatures.
    • Fig. S29. Results of cyclic mechanical test at 1273 K and that of the following test at other temperatures for the same samples.
    • Fig. S30. The relationship between compressed density and Young’s modulus with strain.
    • Legends for movies S1 to S4
    • References (6080)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). In situ optical observation for compress-release cycles of the 3DGraphene foam at 4 K and corresponding stress-strain transient curves.
    • Movie S2 (.mp4 format). In situ optical observation for compress-release cycles of the 3DGraphene foam at 1273 K and corresponding stress-strain transient curves.
    • Movie S3 (.mp4 format). In situ SEM observation for compress-release cycles of the 3DGraphene foam at 4 K.
    • Movie S4 (.mp4 format). In situ SEM observation for compress-release cycles of the 3DGraphene foam at 1273 K.

    Files in this Data Supplement:

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