Plastic Forming of Graphene Oxide Membranes into 3D Structures

Layered Assembly of Graphene Oxide Paper for Mechanical Structures

Graphene oxide (GO) paper is an attractive material because of high stiffness and strength, light weight, and multiple functionalities. While these properties are now widely exploited in nanoinclusions or flat sheets, three-dimensional (3D) structures from GO paper are not widely studied because of a lack of suitable processing methods. In this study, we report a layered assembly method to make stiff and strong 3D GO structures with the aid of a sodium tetraborate (borax) solution. By comparing mechanical properties of assembled GO paper using water or borax solution, we found that the borax-assembled layers had the highest stiffness. To demonstrate the versatility of our assembly protocol, we then fabricated a variety of 3D structures including I-beams, cylindrical tubes, and bridge-like structures from GO paper. These GO structures were stiff and light weight, and the stiffness to mass ratio was around 2-4 times higher than other polymer samples including cellulose, fluorinated ethylene propylene, and poly(vinyl alcohol). The versatile processing method to make stiff and strong GO structures will enable new engineering applications where nonplanar GO structures are required.

Fabrication of graphene-based porous materials: traditional and emerging approaches

The anisotropic nature of ‘graphenic’ nanosheets enables them to form stable three-dimensional porous materials. The use of these porous structures has been explored in several applications including electronics and batteries, environmental remediation, energy storage, sensors, catalysis, tissue engineering, and many more. As method of fabrication greatly influences the final pore architecture, and chemical and mechanical characteristics and performance of these porous materials, it is essential to identify and address the correlation between property and function. In this review, we report detailed analyses of the different methods of fabricating porous graphene-based structures – with a focus on graphene oxide as the base material – and relate these with the resultant morphologies, mechanical responses, and common applications of use. We discuss the feasibility of the synthesis approaches and relate the GO concentrations used in each methodology against their corresponding pore sizes to identify the areas not explored to date.

Due to their anisotropic nature, graphene nanosheets can be used to form 3-dimensional porous materials using template-free and template-directed methodologies. These fabrication strategies are found to influence the properties of the final structure.

Precise Thermoplastic Processing of Graphene Oxide Layered Solid by Polymer Intercalation

The processing capability is vital for the wide applications of materials to forge structures as-demand. Graphene-based macroscopic materials have shown excellent mechanical and functional properties. However, different from usual polymers and metals, graphene solids exhibit limited deformability and processibility for precise forming. Here, we present a precise thermoplastic forming of graphene materials by polymer intercalation from graphene oxide (GO) precursor. The intercalated polymer enables the thermoplasticity of GO solids by thermally activated motion of polymer chains. We detect a critical minimum containing of intercalated polymer that can expand the interlayer spacing exceeding 1.4 nm to activate thermoplasticity, which becomes the criteria for thermal plastic forming of GO solids. By thermoplastic forming, the flat GO-composite films are forged to Gaussian curved shapes and imprinted to have surface relief patterns with size precision down to 360 nm. The plastic-formed structures maintain the structural integration with outstanding electrical (3.07 × 10⁵ S m^-1) and thermal conductivity (745.65 W m^-1 K^-1) after removal of polymers. The thermoplastic strategy greatly extends the forming capability of GO materials and other layered materials and promises versatile structural designs for more broad applications.

Hydroplastic Micromolding of 2D Sheets

Processing 2D sheets into desired structures with high precision is of great importance for fabrication and application of their assemblies. Solution processing of 2D sheets from dilute dispersions is a commonly used method but offers limited control over feature size precision owing to the extreme volume shrinkage. Plastic processing from the solid state is therefore a preferable approach to achieve high precision. However, plastic processing is intrinsically hampered by strong interlayer interactions of the 2D sheet solids. Here, a hydroplastic molding method to shape layered solids of 2D sheets with micrometer-scale precision under ambient conditions is reported. The dried 2D layered solids are plasticized by intercalated solvents, affording plastic near-solid compounds that enable local plastic deformation. Such an intercalated solvent-induced hydroplasticity is found in a broad family of 2D materials, for example graphene, MoS₂ , and MXene. The hydroplastic molding enables fabrication of complex spatial structures (knurling, origami) and microimprinted tubular structures down to diameters of 390 nm with good fidelity. The method enhances the structural accuracy and enriches the structural diversity of 2D macroassemblies, thus providing a feasible strategy to tune their electrical, optical, and other functional properties.