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National Physical Laboratory

Innovation

Quality Control for Liquid Dispersions of 2D Materials

NPL demonstrates technique at University of Manchester

Published: Wednesday, July 26, 2023 - 11:01

Graphene and related 2D materials have the potential to disrupt technologies such as energy storage devices, composites, and electronics through their exceptional material properties. Depending on the material, these can include properties such as high electrical conductivity, high mechanical strength, and high thermal conductivity.

However, when 2D materials are produced at industrial scale, their properties can differ from materials produced in a laboratory.

Liquid phase exfoliation (LPE) is one of the most widely used methods for producing 2D materials at scale. With this method, bulk powders, such as graphite, are perturbed in an organic solvent to generate shear forces and break the 2D layers apart into smaller nanomaterials—a process known as exfoliation. However, nanoplatelet dispersions produced with this method often contain unexfoliated bulk particles, exhibit a large variation in particle size, and the surface chemistry can vary with the addition of functional chemical groups introduced during synthesis.

These properties can all affect the performance of these materials when they are embedded in final products. This means that to optimize the performance of 2D materials and enable their commercialization, we need to be able to measure the chemical and structural properties of nanoplatelets in dispersions.

Currently, several analysis techniques can be used to measure critical material properties of 2D materials, with several of these methods now standardized. However, these techniques can often be lengthy, expensive, measure only a limited sample population, require specialist knowledge to operate, and require dry samples, which makes them unsuitable for use in a manufacturing facility.

There is a strong need to develop rapid, cost-effective tools to efficiently measure 2D materials properties in liquid dispersions and allow for their optimization. Ideally, the measurement should be performed at the production line to enable rapid feedback and optimization of exfoliation parameters for product development.

The solution

To address this need, the U.K.’s National Physical Laboratory (NPL) developed a new method for characterizing 2D materials in dispersion using nuclear magnetic resonance (NMR) proton relaxation.This technique measures the relaxation time of protons in solvent molecules, which NPL has demonstrated can be correlated to changes in specific surface area or surface chemistry of 2D materials in dispersion. The advantages of NMR proton relaxation are the relatively low cost, fast analysis time (in the order of seconds), and the fact that materials can be measured directly in a liquid, allowing it to be operated at the production line.

NPL validated this method by comparing graphene properties measured with NMR proton relaxation to several more accurate characterization techniques, as detailed in two publications focused on graphene’s structural properties and chemical properties. During a recent visit at the Graphene Engineering Innovation Centre (GEIC) at the University of Manchester, NPL demonstrated the use of this technique to several 2D material manufacturers with a practical demonstration of the potential of this technique for characterizing industrial materials.

The impact

The use of a benchtop NMR relaxation instrument with real-world industrial samples demonstrated the feasibility of this method for the rapid quality control of 2D materials in liquid dispersions. This method is relatively low-cost and offers companies a solution to monitor the degree of exfoliation of their dispersions without needing advanced, expensive characterization tools. This solution could help in tuning the exfoliation parameters employed, and ultimately optimize the material for selected applications. The optimization of 2D materials for advanced applications, such as the reduction of carbon emissions, will ultimately lead to huge savings for companies and the development of more efficient real-world products.

‘As a producer of graphene nanoplatelets, this technique is of great interest to us.’
—Thomas Raine, First Graphene (U.K.)

NPL is now working with instrument manufacturers, as well as material producers, to optimize the method and move it out of the laboratory to become part of the industrial process itself.

Sofia Marchesini, higher research scientist at NPL, says, “I am excited about the potential of this technique as a quality control process to monitor the manufacturing of nanomaterials and product formulations. These measurements are fast to perform, and the setup is compatible with flow-through experiments, which means it could be integrated into an industrial production line.”

“NPL’s published work and dissemination of a NMR proton relaxation method, particularly through the demonstration at the GEIC to First Graphene (U.K.), has shown that this rapid test method could be used for quantifying specific surface area and stability of graphene dispersions,” says Thomas Raine, senior development chemist at First Graphene (U.K.). “As a producer of graphene nanoplatelets, this technique is of great interest to us as a potential quality control tool to understand batch-to-batch variation at the manufacturing line itself, to enable faster product development, and ensure product quality.” 

First published by the National Physical Laboratory.

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National Physical Laboratory

Founded in 1900, the National Physical Laboratory (NPL) is a world-leading center for the development and exploitation of measurement science, technology, related standards, and best practices in a diverse range of technical areas and market sectors. As the United Kingdom’s National Measurement Institute, NPL capabilities underpin the U.K. National Measurement System (NMS), ensuring consistency and traceability of measurements in support of U.K. and overseas customer interests.