Graphene and other atomically thin 2D nanomaterials (e.g. MoS2) are small nanoparticles that are used in a variety of high-tech applications, including new generation batteries, electrical cables, conductive plastics, new-generation food packaging, high-performance tires, biotech devices and others. These materials are in most applications produced and processed in a liquid state, in the form of a mixture of particles suspended in a liquid. When such liquid mixture is processed, the performance of the resulting material depends crucially on how the liquid and its particulate constituents flow. We call this new branch of science the "fluid dynamics of graphene" or "graphene hydrodynamics".
The challenge that the FlexNanoFlow project aims to address is the poor understanding of how graphene and other 2D nanomaterial particles behave when they are processed in liquids. This knowledge is crucially important to model or predict the flow of 2D nanomaterials in coatings, 3D printing techniques, sprays, extrusion processes that are commonly employed to produce items we use every day.
The specific objectives of the project are to use a combination of theoretical, computational and experimental techniques to understand the effect of the flow on how the particles orient when suspended in the liquid, how the particles deform (by folding like sheets of paper) and how they break under the action of the strong shear forces produced by the flow. Finally, we aimed to understand how these particles adsorb at fluid interfaces (for instance the surface of a liquid drop) and the resulting semi-solid particle layer deform under compression.
The overarching conclusion the team has reached thanks to ERC funding is that graphene and 2D nanomaterials do not behave in flow like other commonly employed nanoparticles do. They have very specific behaviour, rooted in their extremely small thickness, surface slip properties, and ability to bend. For example, we have discovered that graphene and certain other 2D nanomaterials do not behave like other anisotropic nanoparticles because they do not rotate in a shear flow. As a result of this absence of rotation, 2D nanoparticles can give an extraordinary effect: a reduction in viscosity of the liquid by adding solid material. No other nanoparticle additive has been demonstrated to give such effect. We have also elucidated the enormous importance that bending deformations have on the breakup of multilayer 2D nanomaterials. Such knowledge is important to develop software tools to quantify the yield of methods to produce 2D nanomaterials on an industrial scale.
