Periodic Reporting for period 3 - FlexNanoFlow (Ultra-flexible nanostructures in flow: controlling folding, fracture and orientation in large-scale liquid processing of 2D nanomaterials)
Reporting period: 2019-10-01 to 2021-03-31
The ERC project FLEXNANOFLOW promises to make a big step in the direction of understanding how 2D nanomaterials exfoliate, deform and interact in liquids, based on a comprehensive theoretical and computational framework that combines multiscale computations and experiments. Such framework is the first of its kind. The project will enable the EU's scientific community to retain and advanced knowledge of these extraordinary materials, and EU's industry to lead the way in the technological exploitation of graphene, a truly European invention.
Secondly, we have investigated how graphene exfoliation works at the level of a single multilayer nanoparticle. Combining multiscale simulations and theory we have been able to quantify thresholds for the shear rate leading to exfoliation, and derive practical expressions that will enable practitioners to, for example, decide the power of a mixer that could lead to optimal exfoliation. These models are the first appearing in the literature that have been rigorously justified by comparison against high-resolution simulations and molecular dynamics. We have also investigated the role of different solvents in reducing inter-layer adhesion and triggering exfoliation in liquids, for the first time evaluating the coupling between adhesion and flow in configurations similar to those occurring in practice. Here the promise is that with the new understanding enabled by the ERC project FlexNanoFlow we will be able to develop scalable methods to produce graphene and other 2D nano materials on the industrial scale (meaning, tons of material!) required by market applications.
The result that we are most excited about is the discovery of the dramatic effect that hydrodynamic slip has on the rotational dynamics of graphene. That a slip length of few nanometers can change the dynamics of graphene particles that can be several microns in length is truly an unexpected result. In the future, we would like to better understand the effects of particle flexibility and increase in particle concentration in the fluid. We are well on track to deliver on these aspects by the end of the project.
We have also pushed scientific boundaries in terms of improving our understanding of the micromechanics of liquid-phase exfoliation. So far we have proposed first-of-their-kind theoretical models for predicting the shear rate leading to exfoliation of graphene. We have proposed a sliding model that should work well with small nanosheets, and a peeling model which should be applied to larger nanosheets. After exploring critical shear rate threshold, what we are now interested in is the time-scale of exfoliation. If I apply a critical shear rate, how long will it take for the particle to exfoliate? At the end of the ERC project we will hopefully have investigated model problems to understand the dynamics of exfoliation, carrying out simulations and conducting experiments on model particles to guide our thought process.
Finally, we will produce new results for the hydrodynamic and capillary interaction of 2D nanomaterials with fluid interfaces. The understanding of the motion of graphene platelets in unbounded bulk liquids we have obtained in the first part of the project constitutes a solid basis for these future investigations.