Researchers from the Institute for Integrated Cell-Material Sciences (iCeMS) at Kyoto University have developed a novel but simple technique called “diffusion driven layer-by-layer assembly” to construct graphene into porous three-dimensional structures for applications in devices such as batteries and supercapacitors.

Their study was recently published in the journal Nature Communications.

The problem they addressed is the difficulty of piecing together graphene sheets into useful larger structures. The researchers borrowed a principle from polymer chemistry and developed it into a technique to assemble graphene into porous 3D architectures while preventing stacking between the sheets.

By putting graphene oxide (an oxidized form of graphene) into contact with an oppositely charged polymer, the two components could form a stable composite layer, a process also known as “interfacial complexation.”

“Interestingly, the polymer could continuously diffuse through the interface and induce additional reactions, which allowed the graphene-based composite to develop into thick multi-layered structures. Hence, we named this process ‘diffusion driven layer-by-layer assembly,'” explained Jianli Zou, a co-investigator in the project.

The resulting products display a foam-like porous structure that is tunable from ultra-light to highly dense by simple changes in experimental conditions. The process is also scalable for creating large-area films for use as electrodes and membranes for energy generation or storage.

Franklin Kim, the principal investigator of the study, said the new technique will also be able to serve as a general method for the assembly of a much wider range of nanomaterials.

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Abstract of Diffusion driven layer-by-layer assembly of graphene oxide nanosheets into porous three-dimensional macrostructures

Despite recent progress in preparing numerous types of nanosheets, it remains a difficult challenge to assemble the tiny building blocks into functional macroscale architectures suitable for practical applications. Here we introduce a diffusion driven layer-by-layer assembly process and demonstrate its application for the construction of graphene oxide sheets into various three-dimensional structures. This process involves complexation of the negatively charged graphene oxide sheets and positively charged branched polyethylenimine at a given interface. We find that the diffusion of branched polyethylenimine molecules allows the complex to continuously grow into foam-like frameworks with tunable porosities. Furthermore, the assembly process is quite robust and can be utilized in various configurations such as to create free-standing architectures with tailored shapes or patterned films on a substrate. With such useful features, we believe that this technique may serve as a valuable tool for the assembly of nanomaterials.