Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - LENSD (Liquid Exfoliation of Nanomaterials using Spinning Discs)

Teaser

Two-dimensional (2D) materials are a class of nanomaterials which posses an extraordinary range of properties. One of the most well-known of these is graphene. Many beneficial applications for graphene and other 2D materials have been suggested including opto-electronics...

Summary

Two-dimensional (2D) materials are a class of nanomaterials which posses an extraordinary range of properties. One of the most well-known of these is graphene. Many beneficial applications for graphene and other 2D materials have been suggested including opto-electronics, semiconductors, biomedical sensors, tissue engineering, drug delivery, energy conversion and storage. All of these applications are within three broad sectors that have the biggest impact on today’s society: Information Communication Technology (ICT), Biomedicine and Energy. It is therefore imperative that these exciting materials can be exploited on a large scale to address the global challenges that society faces. Scalable production is one of the main challenges limiting the widespread introduction of graphene and other 2D materials to our future technologies. In the past decade, research into production has resulted in numerous variations of bottom-up and top-down methods, whose suitability can often depend on the requirements of the intended application. Non-oxidising liquid phase exfoliation is one top-down method which has been demonstrated to produce both high quality and high concentrations of material, compared to the other methods available at least. The material is also produced in the form of a liquid dispersion, making it readily useable for applications such as printed electronics, battery and supercapacitor electrodes, and composites. Although this method has shown promise for scale-up, production output remains low. There are a number of reasons for this including: 1. lab-scale techniques are predominantly batch processes, with performances that do not scale well, or in an easily predictable way; 2. the fundamental physical mechanisms driving exfoliation in liquids are not fully understood. This project involves a multidisciplinary research effort, integrating materials science, chemical engineering, and mechanical engineering disciplines. The overall objective is to address the shortcomings noted above, using flow over a spinning disc as the test case. Combining nanomaterial characterisation techniques, with high fidelity measurements and direct numerical simulations of the hydrodynamics, unique insights into the exfoliation process have been obtained. Using this test case, the critical criteria for production have been determined, with general application to all liquid phase exfoliation techniques.

Work performed

Experiments (synthesis, transport phenomena), material characterisation, numerical simulations (computational fluid dynamics), data analyses, and engineering and design innovation were implemented. Experiments were performed to produce graphene from graphite using liquid phase exfoliation, and simultaneously conduct high-fidelity fluid mechanics measurements (high speed imagery, particle image/tracking velocimetry). Material characterisation, spanning micrometre to nanometre scales, was performed using specialist spectroscopy (Raman, UV-vis-nIR, XPS) and microscopy techniques (optical, TEM, SEM, AFM). Direct numerical simulations of multiphase flows were performed using high performance computing facilities, and open-source codes, to study the fluid stress fields corresponding to the liquid phase exfoliation experiments. Data analyses were used to post-process experimental and numerical data, and to correlate the material characterisation and hydrodynamics results. Finally, engineering and design innovation was used to realise creative concepts that were guided by the scientific outputs from the project.

Final results

Using a combination of direct numerical simulations and experiments, an unprecedented level of detail on complex interfacial, thin film flows has been obtained. These insights have been used to investigate important spinning disc parameters for graphene exfoliation. It also has general relevance to other production applications (i.e. pharmaceuticals). A critical exfoliation criterion, describing the strain rate necessary to produce graphene from graphite in a solvent suspension, has been quantitatively confirmed. Prior to this work, the criterion was based on qualitative microscopy measurements. Although a critical strain rate is necessary to exfoliate two-dimensional nanomaterials, the residence time of the production process was found to have an equally significant influence on production output. There have been additional project innovations, with broad academic and industrial relevance, that notably exceed the original project objectives. This includes the development of: 1. A novel liquid phase exfoliation technique that delivers an order-of-magnitude increase in production output compared to batch production techniques currently used by industry; and 2. A real-time graphene production monitoring system, and demonstration of Internet-of-Things (IoT) integration towards deployment in an Industry 4.0 environment. The combination of novel scientific outputs with practical innovations, has already resulted in a sufficient research maturity to engage leading European manufacturing companies. These interactions will ensure translation of the research outputs into industry and for the benefit of society.