Abstract
One of the challenges in the processing of advanced composite materials with 2D reinforcement is their extensive agglomeration in the matrix. 3D architecture of 2D graphene sheets into a Graphene Foam (GrF) assembly has emerged as an effective way to overcome agglomeration. The highly reticulated network of branches and nodes of GrF offers a seamless pathway for photon and electron conduction in the matrix along with improved mechanical properties. 3D GrF nano-filler is often fabricated by chemical vapor deposition (CVD) technique, which demands high energy, slow deposition rate, and restricting production to small scale. This work highlights freeze-drying (FD) technique to produce 3D graphene nanoplatelets (GNP) foam with a similar hierarchical structure to the CVD GrF. The FD technique using water as the main chemical in 3D GNP foam production is an added advantage. The flexibility of the FD in producing GNP foams of various pore size and morphology is elucidated. The simplicity with which one can engineer thermodynamic conditions to tailor the pore shape and morphology is presented here by altering the GNP solid loading and mold geometry. The FD 3D GNP foam is mechanically superior to CVD GrF as it exhibited 1280 times higher elastic modulus. However, thermal diffusivity of the FD GNP foam is almost 0.5 times the thermal diffusivity of the CVD GrF due to the defects in GNP particles and pore architecture. The versatility in GNP foam scalability and compatibility to form foam of other 1D and 2D material systems (e.g., carbon nanotubes, boron nitride nanotubes, and boron nitride nanoplatelets) brings a unique dimensionality to FD as an advanced engineering foam development process.
Highlights
Accepted: 8 February 2021Over the past five decades, extensive progress has been achieved in understanding the effect of reinforcing materials in enhancing the matrix properties [1,2,3,4]
The 3D graphene nanoplatelets (GNP) foam produced by FD is compared with the chemical vapor deposition (CVD) Graphene Foam (GrF) to understand the effect of processing on the mechanical and thermal properties
If ∆σ is negative, the GNP particles will be trapped inside the freezing ice crystal, inducing the formed foamy structures’ low structural integrity
Summary
Over the past five decades, extensive progress has been achieved in understanding the effect of reinforcing materials in enhancing the matrix properties [1,2,3,4]. Lack of homogeneous distribution of 2D Gr in the non-conducting (both thermal and electrical) material matrix, as shown in Figure 3a [low temperature co-fired dense ceramic reinforced with graphene nano-platelets (GNP)] produced by spark plasma sintering), causes a discontinuity in the contact between Gr flakes, as represented, affecting the phonon and electron conduction path, limiting the thermal and electrical conductivity in the composite [12,13]. Porous metal foam with a reticulated structure, typically nickel the desired with pore shape and size, is chosen as the graphene deposition template. The 3D GNP foam produced by FD is compared with the CVD GrF to understand the effect of processing on the mechanical and thermal properties. This study demonstrates that 3D foams of other nanomaterials can be produced by the simple, eco-friendly, and cost-effective FD technique
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