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Understanding Mechanical Response of Elastomeric Graphene Networks.

Ni N, Barg S, Garcia-Tunon E, Macul Perez F, Miranda M, Lu C, Mattevi C, Saiz E - Sci Rep (2015)

Bottom Line: In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features.A better restoration of the graphitic nature also has a considerable effect.These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

View Article: PubMed Central - PubMed

Affiliation: Centre for Advanced Structural Ceramics, Department of Materials, Imperial College London, London SW7 2AZ, UK.

ABSTRACT
Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

No MeSH data available.


Related in: MedlinePlus

Characterization of the porous networks.(a) Raman spectra of the as prepared GO-PN and rGO-PN treated at 473 and 1223K. (b) XRD spectra of GO-sus, GO-PN and rGO-PN. (c–f) TEM observations. In (c) it is shown the presence of highly curved monolayer to few layer flakes in the rGO-PN. (d) In the high resolution phase contrast image of the edge of a single layer flake, in-plane carbon atoms are resolved and a variety of n-membered carbon rings can be seen. In (e) and (f) it is shown that the flakes composing the wall are entangled with each other.
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f3: Characterization of the porous networks.(a) Raman spectra of the as prepared GO-PN and rGO-PN treated at 473 and 1223K. (b) XRD spectra of GO-sus, GO-PN and rGO-PN. (c–f) TEM observations. In (c) it is shown the presence of highly curved monolayer to few layer flakes in the rGO-PN. (d) In the high resolution phase contrast image of the edge of a single layer flake, in-plane carbon atoms are resolved and a variety of n-membered carbon rings can be seen. In (e) and (f) it is shown that the flakes composing the wall are entangled with each other.

Mentions: Thermally reduced GO-PNs (rGO-PNs) retained the freeze casted microstructure (Fig. 2f). It has been shown in our previous work that most of the organic additives (∼91%) are removed during the heat treatment4. Raman spectra of the GO-PNs and rGO-PNs confirm the formation of predominantly crystalline rGO upon thermal reduction (Fig. 3a), indicated by the sharpening of both the D and G peaks and the enhancement of the 2D peak3839. The spectra from samples treated at 1223 K exhibits more pronounced 2D peak than from that reduced at 473 K, suggesting that the crystallinity of the rGO increases with increasing treatment temperature, in agreement with our previous observations4. The intensity ratio between peak D and G (ID/IG) increases from ∼0.7 for GO-PNs, to ∼0.9 for rGO-PNs reduced at 473K and to ∼1.2 for rGO-PNs reduced at 1223K, corresponding to a decrease in the defect concentration as expected for carbon material with relatively high defect contents3840. It is noted that the ID/IG ratio for small flake samples is very similar to that for big flake samples, in both unreduced and reduced conditions, which indicates a similar atomic defect concentration in both samples. X-ray diffraction (XRD) patterns (Fig. 3b) provide further evidence on the removal of major oxygen-containing groups: the d-spacing of GO flakes in suspension is ∼0.83 nm and decreased to ∼0.34 nm in the rGO-PN, which is the same as the graphite interlayer distance. TEM analysis of the rGO-PN samples treated at 1223 K (Fig. 3c–f) reveals that the walls of the porous structure is composed of single, few-layer to multi-layer (up to ∼15 layers) graphene flakes having an interlayer spacing measured to be ∼0.35 nm, in good agreement with the spacing calculated from XRD. TEM micrographs (Fig. 3d) also reveal that the rGO flakes are highly curved with the presence of a variety of n-membered carbon rings, which is expected for rGO with a considerable defect density as indicated by the Raman spectra. It is noted that the flakes that compose the wall are entangled with each other (Fig. 3e,f).


Understanding Mechanical Response of Elastomeric Graphene Networks.

Ni N, Barg S, Garcia-Tunon E, Macul Perez F, Miranda M, Lu C, Mattevi C, Saiz E - Sci Rep (2015)

Characterization of the porous networks.(a) Raman spectra of the as prepared GO-PN and rGO-PN treated at 473 and 1223K. (b) XRD spectra of GO-sus, GO-PN and rGO-PN. (c–f) TEM observations. In (c) it is shown the presence of highly curved monolayer to few layer flakes in the rGO-PN. (d) In the high resolution phase contrast image of the edge of a single layer flake, in-plane carbon atoms are resolved and a variety of n-membered carbon rings can be seen. In (e) and (f) it is shown that the flakes composing the wall are entangled with each other.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4562249&req=5

f3: Characterization of the porous networks.(a) Raman spectra of the as prepared GO-PN and rGO-PN treated at 473 and 1223K. (b) XRD spectra of GO-sus, GO-PN and rGO-PN. (c–f) TEM observations. In (c) it is shown the presence of highly curved monolayer to few layer flakes in the rGO-PN. (d) In the high resolution phase contrast image of the edge of a single layer flake, in-plane carbon atoms are resolved and a variety of n-membered carbon rings can be seen. In (e) and (f) it is shown that the flakes composing the wall are entangled with each other.
Mentions: Thermally reduced GO-PNs (rGO-PNs) retained the freeze casted microstructure (Fig. 2f). It has been shown in our previous work that most of the organic additives (∼91%) are removed during the heat treatment4. Raman spectra of the GO-PNs and rGO-PNs confirm the formation of predominantly crystalline rGO upon thermal reduction (Fig. 3a), indicated by the sharpening of both the D and G peaks and the enhancement of the 2D peak3839. The spectra from samples treated at 1223 K exhibits more pronounced 2D peak than from that reduced at 473 K, suggesting that the crystallinity of the rGO increases with increasing treatment temperature, in agreement with our previous observations4. The intensity ratio between peak D and G (ID/IG) increases from ∼0.7 for GO-PNs, to ∼0.9 for rGO-PNs reduced at 473K and to ∼1.2 for rGO-PNs reduced at 1223K, corresponding to a decrease in the defect concentration as expected for carbon material with relatively high defect contents3840. It is noted that the ID/IG ratio for small flake samples is very similar to that for big flake samples, in both unreduced and reduced conditions, which indicates a similar atomic defect concentration in both samples. X-ray diffraction (XRD) patterns (Fig. 3b) provide further evidence on the removal of major oxygen-containing groups: the d-spacing of GO flakes in suspension is ∼0.83 nm and decreased to ∼0.34 nm in the rGO-PN, which is the same as the graphite interlayer distance. TEM analysis of the rGO-PN samples treated at 1223 K (Fig. 3c–f) reveals that the walls of the porous structure is composed of single, few-layer to multi-layer (up to ∼15 layers) graphene flakes having an interlayer spacing measured to be ∼0.35 nm, in good agreement with the spacing calculated from XRD. TEM micrographs (Fig. 3d) also reveal that the rGO flakes are highly curved with the presence of a variety of n-membered carbon rings, which is expected for rGO with a considerable defect density as indicated by the Raman spectra. It is noted that the flakes that compose the wall are entangled with each other (Fig. 3e,f).

Bottom Line: In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features.A better restoration of the graphitic nature also has a considerable effect.These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

View Article: PubMed Central - PubMed

Affiliation: Centre for Advanced Structural Ceramics, Department of Materials, Imperial College London, London SW7 2AZ, UK.

ABSTRACT
Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

No MeSH data available.


Related in: MedlinePlus