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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

Energy loss coefficients of porous networks (a) produced with different conditions and (b) under a cyclic compressive test.(c) Energy-absorption diagrams for the porous networks produced and tested at different conditions. Parallel black dash-dot lines (arrowed) connect data for samples with same density but obtained at different strain rates, giving a family of lines of constant sample density. (d) Comparison between the porous networks and polymer foams in the energy-absorption diagram. Unless specified, the fabrication and testing conditions are: big GO flakes, lamellar structure, 10 K min−1 cold finger cooling rate during freeze casting, heat treatment at 1223 K and compressive test at strain rate of 0.001 s−1. As noted in the main text, the lamellar structure has a cell size of ∼15 μm and the size is approximately doubled by decreasing the cooling rate from 10 K min−1 to 1 K min−1 for the sample labelled as “Lamellar (cell size × 2)”.
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f8: Energy loss coefficients of porous networks (a) produced with different conditions and (b) under a cyclic compressive test.(c) Energy-absorption diagrams for the porous networks produced and tested at different conditions. Parallel black dash-dot lines (arrowed) connect data for samples with same density but obtained at different strain rates, giving a family of lines of constant sample density. (d) Comparison between the porous networks and polymer foams in the energy-absorption diagram. Unless specified, the fabrication and testing conditions are: big GO flakes, lamellar structure, 10 K min−1 cold finger cooling rate during freeze casting, heat treatment at 1223 K and compressive test at strain rate of 0.001 s−1. As noted in the main text, the lamellar structure has a cell size of ∼15 μm and the size is approximately doubled by decreasing the cooling rate from 10 K min−1 to 1 K min−1 for the sample labelled as “Lamellar (cell size × 2)”.

Mentions: Energy loss coefficients were calculated by taking the ratio between the energy dissipated within the materials and the work done by compression. Their variation with the density and permanent deformation is shown in Fig. 8a. Samples with densities >∼2–3 mg/cm3 are superelastic and their energy loss coefficient is as high as 0.84 at a density of 2.5 mg/cm3 for samples with larger GO flakes and thicker walls (larger cells). Furthermore, a good cycling performance is maintained, stabilizing the coefficient values around 0.55 after the first four compression cycles (Fig. 8b). The permanent deformation caused by the compression test decreases with increasing density as a result of increasing structural integrity (indicated by the blue solid line in Fig. 8a). On the other hand, the dependence of energy loss coefficient with density shows the presence of a minimum (indicated by the red solid line in Fig. 8a). The effect of strain rate on the energy dissipation efficiency also appears to depend on the sample density (or inherently the recoverability of the sample). At low densities when the structure does not recover, an increase in strain rate by 3 orders of magnitude (from 0.001 s−1 to 1 s−1) results in a higher amount of permanent deformation. At high densities the strain rate shows little effect on the amount of permanent deformation.


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)

Energy loss coefficients of porous networks (a) produced with different conditions and (b) under a cyclic compressive test.(c) Energy-absorption diagrams for the porous networks produced and tested at different conditions. Parallel black dash-dot lines (arrowed) connect data for samples with same density but obtained at different strain rates, giving a family of lines of constant sample density. (d) Comparison between the porous networks and polymer foams in the energy-absorption diagram. Unless specified, the fabrication and testing conditions are: big GO flakes, lamellar structure, 10 K min−1 cold finger cooling rate during freeze casting, heat treatment at 1223 K and compressive test at strain rate of 0.001 s−1. As noted in the main text, the lamellar structure has a cell size of ∼15 μm and the size is approximately doubled by decreasing the cooling rate from 10 K min−1 to 1 K min−1 for the sample labelled as “Lamellar (cell size × 2)”.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f8: Energy loss coefficients of porous networks (a) produced with different conditions and (b) under a cyclic compressive test.(c) Energy-absorption diagrams for the porous networks produced and tested at different conditions. Parallel black dash-dot lines (arrowed) connect data for samples with same density but obtained at different strain rates, giving a family of lines of constant sample density. (d) Comparison between the porous networks and polymer foams in the energy-absorption diagram. Unless specified, the fabrication and testing conditions are: big GO flakes, lamellar structure, 10 K min−1 cold finger cooling rate during freeze casting, heat treatment at 1223 K and compressive test at strain rate of 0.001 s−1. As noted in the main text, the lamellar structure has a cell size of ∼15 μm and the size is approximately doubled by decreasing the cooling rate from 10 K min−1 to 1 K min−1 for the sample labelled as “Lamellar (cell size × 2)”.
Mentions: Energy loss coefficients were calculated by taking the ratio between the energy dissipated within the materials and the work done by compression. Their variation with the density and permanent deformation is shown in Fig. 8a. Samples with densities >∼2–3 mg/cm3 are superelastic and their energy loss coefficient is as high as 0.84 at a density of 2.5 mg/cm3 for samples with larger GO flakes and thicker walls (larger cells). Furthermore, a good cycling performance is maintained, stabilizing the coefficient values around 0.55 after the first four compression cycles (Fig. 8b). The permanent deformation caused by the compression test decreases with increasing density as a result of increasing structural integrity (indicated by the blue solid line in Fig. 8a). On the other hand, the dependence of energy loss coefficient with density shows the presence of a minimum (indicated by the red solid line in Fig. 8a). The effect of strain rate on the energy dissipation efficiency also appears to depend on the sample density (or inherently the recoverability of the sample). At low densities when the structure does not recover, an increase in strain rate by 3 orders of magnitude (from 0.001 s−1 to 1 s−1) results in a higher amount of permanent deformation. At high densities the strain rate shows little effect on the amount of permanent deformation.

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