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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

Typical compressive properties of the porous networks.(a) Compressive stress-strain curves tested at the maximum strain of 80% for two rGO-PN samples of similar density (ρ ∼ 11 mg/cm3) produced using big or small GO flakes. (b) The stress-strain curve for a rGO-PN (ρ ∼ 4.5 mg/cm3) tested at the maximum strain of 50% for 10 cycles. The strain rate for these test were 0.001 s−1. (c) The relative recovery after 50% strain for a rGO-PN with ρ ∼ 4.5 mg/cm3. Unless it is stated specifically the porous networks were produced using big GO-flakes with a cold finger cooling rate of 10 K min−1 during ice templating followed by heat treatment at 1223 K.
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f4: Typical compressive properties of the porous networks.(a) Compressive stress-strain curves tested at the maximum strain of 80% for two rGO-PN samples of similar density (ρ ∼ 11 mg/cm3) produced using big or small GO flakes. (b) The stress-strain curve for a rGO-PN (ρ ∼ 4.5 mg/cm3) tested at the maximum strain of 50% for 10 cycles. The strain rate for these test were 0.001 s−1. (c) The relative recovery after 50% strain for a rGO-PN with ρ ∼ 4.5 mg/cm3. Unless it is stated specifically the porous networks were produced using big GO-flakes with a cold finger cooling rate of 10 K min−1 during ice templating followed by heat treatment at 1223 K.

Mentions: The porous networks show different behaviour under compression depending on their density4. In this work we mainly investigate the mechanical response of elastomeric rGO-PNs with densities between 1.5 to 12 mg/cm3, and an example is shown in Fig. 4a. Upon compression to a strain (ε) of 0.8, the stress-strain curve shows first a predominantly linear elastic region that can be associated to cell wall bending41, followed by a change in the slope that can be regarded as “elastic collapse” at strains typically <10% and a plateau region with a gradual increase in slope up to strains of ∼0.6. Finally a “densification” stage characterized by rapidly increasing stress with strain is observed. Overall, this behaviour resembles more an elastomeric foam where the elastic collapse is determined by buckling of the walls41. In situ SEM observation during compression of a lamellar network appears to confirm this collapse mechanism (Supplementary movie S1). The porous network fails via propagation of wall buckling at preferred locations (where the local stress field is maximized by local orientation of the wall). The mechanism for the collapse of the foam-like structure is similar with bending and buckling of the cell walls taking place at preferred stress locations (Supplementary movie S2). Multiple buckling processes, similar to what has been observed in carbon nanotube bundles42, may happen subsequently in different locations before the densification stage. This explains the small slope in the plateau region.


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)

Typical compressive properties of the porous networks.(a) Compressive stress-strain curves tested at the maximum strain of 80% for two rGO-PN samples of similar density (ρ ∼ 11 mg/cm3) produced using big or small GO flakes. (b) The stress-strain curve for a rGO-PN (ρ ∼ 4.5 mg/cm3) tested at the maximum strain of 50% for 10 cycles. The strain rate for these test were 0.001 s−1. (c) The relative recovery after 50% strain for a rGO-PN with ρ ∼ 4.5 mg/cm3. Unless it is stated specifically the porous networks were produced using big GO-flakes with a cold finger cooling rate of 10 K min−1 during ice templating followed by heat treatment at 1223 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Typical compressive properties of the porous networks.(a) Compressive stress-strain curves tested at the maximum strain of 80% for two rGO-PN samples of similar density (ρ ∼ 11 mg/cm3) produced using big or small GO flakes. (b) The stress-strain curve for a rGO-PN (ρ ∼ 4.5 mg/cm3) tested at the maximum strain of 50% for 10 cycles. The strain rate for these test were 0.001 s−1. (c) The relative recovery after 50% strain for a rGO-PN with ρ ∼ 4.5 mg/cm3. Unless it is stated specifically the porous networks were produced using big GO-flakes with a cold finger cooling rate of 10 K min−1 during ice templating followed by heat treatment at 1223 K.
Mentions: The porous networks show different behaviour under compression depending on their density4. In this work we mainly investigate the mechanical response of elastomeric rGO-PNs with densities between 1.5 to 12 mg/cm3, and an example is shown in Fig. 4a. Upon compression to a strain (ε) of 0.8, the stress-strain curve shows first a predominantly linear elastic region that can be associated to cell wall bending41, followed by a change in the slope that can be regarded as “elastic collapse” at strains typically <10% and a plateau region with a gradual increase in slope up to strains of ∼0.6. Finally a “densification” stage characterized by rapidly increasing stress with strain is observed. Overall, this behaviour resembles more an elastomeric foam where the elastic collapse is determined by buckling of the walls41. In situ SEM observation during compression of a lamellar network appears to confirm this collapse mechanism (Supplementary movie S1). The porous network fails via propagation of wall buckling at preferred locations (where the local stress field is maximized by local orientation of the wall). The mechanism for the collapse of the foam-like structure is similar with bending and buckling of the cell walls taking place at preferred stress locations (Supplementary movie S2). Multiple buckling processes, similar to what has been observed in carbon nanotube bundles42, may happen subsequently in different locations before the densification stage. This explains the small slope in the plateau region.

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