Engineering Graphene‐Ceramic 3D Composite Foams by Freeze Drying

Abstract

Nanofillers such as carbon fiber, carbon nanotube (CNT), 2D graphene, and hexagonal boron nitride are a proven reinforcement material at the microscale, leading to enhanced macroscopic property. [1][2][3] However, the augmentation of properties such as superior mechanical strength, increased electrical and thermal properties, and crack confinement in the material matrix is achieved only when the nanofillers are dispersed homogeneously. Until the advent of 2D graphene in 2004, [4,5] CNTs were the dominant nanofiller used in the synthesis of reinforced nanocomposites. CNT's high entanglement affinity, impurities, and challenges associated with processing hindered their application for novel composite materials development. [6][7][8] On the other hand, 2D graphene (Gr), whose material properties are comparable to CNTs, had many other novel physical, chemical, and electronic properties. Experimental and theoretical results boast that a single sheet of 2D graphene formed by the packing of carbon atoms into a honeycomb-like lattice is the strongest material developed to date. [9,10] The 2D graphene exhibits high modulus (%1 TPa), [11] tensile strength (%100 GPa), [11] superior thermal conductivity (3000-5000 W m À1 K À1 ), [12,13] exceptional electron mobility at room temperature (>200 000 cm 2 V À1 s À1 ), [14][15][16] and high transparency (97.7%) to incident light. [17,18] These outstanding physicochemical properties of 2D graphene make it a popular nanofiller for various applications, such as composite engineering materials, sensor, nanoelectronics, biomedical, and catalysis, to name a few. [19] Despite these excellent properties as a nanofiller, 2D graphene results in the aggregation or restacking of sheets due to strong π-π interaction. [20][21][22] Thus, formed nanocomposites exhibit poor mechanical (agglomerates form sites for stress concentration) and deteriorated electrochemical properties due to decreased active surface area. To fully exploit the outstanding properties of 2D graphene, various strategies have been used, such as crumbling the graphene sheets, adding spacers, and stacking 2D graphene into 3D hierarchical architecture. [23,24] Graphene material with 3D architecture, such as foam produced by chemical vapor deposition (CVD), has proved effective against agglomeration, unlike the 2D graphene flakes in the matrix material. The interconnected network of nodes and branches, which is characteristic of a 3D hierarchical structure of graphene foam (GrF), enables uninterrupted pathways to transfer electrons, phonons, and stresses, thus incorporating superior material properties in the reinforced matrix. [25][26][27] The porous 3D architecture in GrF offers low density (<5 mg cm À3 ), high surface area (%850 m 2 g À1 ), stable mechanical properties, accelerated electron and phonon transfer properties due to the reduced inter-sheet junction contact resistance, unlike the 2D graphene sheets.

Orientation-Dependent Thermal and Mechanical Properties of 2D Boron Nitride Nanoplatelet Foams via Freeze-Drying

“…Freeze-drying consists of freezing and sublimation processes, as shown in Figure e. Both processes are governed by thermodynamic parameters that dictate the foam’s pore size, morphology, and orientation . The mold’s thermal gradient, heat transfer direction, and conductivity control the resulting foam morphology …”

“…Both processes are governed by thermodynamic parameters that dictate the foam's pore size, morphology, and orientation. 49 The mold's thermal gradient, heat transfer direction, and conductivity control the resulting foam morphology. 50 During the freeze-drying of 2D BNNP slurry, supercooling lowers deionized water's freezing agent temperature below its freezing point without becoming a solid.…”

Intercalation Engineering of 2D Materials at Macroscale for Smart Human–Machine Interface and Double‐Layer to Faradaic Charge Storage for Ions Separation

“…[70] A report on graphene and ceramic (LTCC) for developing GNP-LTCC foam by mold casting method that maintains controlled thermodynamic process to result in a porous structure. [54] It is easy to infiltrate low viscosity polymers into the porous graphene foam as compared to porous metallic and ceramic which are very challenging to fabricate under extreme temperature and pressure which results in damage and collapsed 3D foam structure. [54] However, coating of 3D foam substrate with a hydrophobic material such as polyvinylidene fluoride [92] and surface roughness of CNTs [92,93] can also introduce hydrophobicity.…”

“…[ 53 ] While CVD acts as an effective nanofiller without any agglomeration in the matrix and pristine graphene foam can be accessed by forming graphene nanoplatelet with ceramic wither with thermally conductive or thermally insulating components. [ 54 ] The CVD method has been useful to deposit graphene vapors using high‐temperature calcination (≈1000 °C) using metal foam such as copper foam [ 55 ] and nickel foam [ 56 ] template ( Figure a). However, the major drawback of this approach is the lengthy template removal process, unavoidable metal residues, and limited choice of metal foam with microstructures.…”

“…[54] It is easy to infiltrate low viscosity polymers into the porous graphene foam as compared to porous metallic and ceramic which are very challenging to fabricate under extreme temperature and pressure which results in damage and collapsed 3D foam structure. [54] However, coating of 3D foam substrate with a hydrophobic material such as polyvinylidene fluoride [92] and surface roughness of CNTs [92,93] can also introduce hydrophobicity. The more hydrophilic surface in graphene foam can be utilized for removal of such as dye, heavy metal, oil, and organic solvents which readily adsorb on more hydrophobic region of graphene foam by a π-π interaction.…”