Foam flows in turbulent liquid exfoliation of layered materials and implications for graphene production and inline characterisation

Surfactants are often used to stabilise two-dimensional (2D) materials in environmentally friendly solvents such as water. Aqueous-surfactant solutions prevent agglomeration of nanosheets through steric and electrostatic repulsion, facilitating the production high concentration nanomaterial dispersions. Turbulent, shear-assisted liquid exfoliation layered precursor produces defect-free by promoting mixing generating sufficiently shear rates overcome out-of-plane van der Waals bonds. In presence a liquid-gas interface, consequence using surfactants turbulent flows is formation foam. this experimental study, batch graphite particles into few-layer graphene was performed kitchen blender modified operate across Reynolds numbers, $Re \sim 10^{5} - 10^{6}$. Foam during operation found influence hydrodynamics process. Measurements on motion indicate that surfactant alters rheology mixture under dynamic conditions changes material flow patterns within device. As result, maximised non-unique. This highlights design selection should consider both molecular scale repulsion effectiveness macroscale Furthermore, multi-phase complex fluids exist aqueous-surfactants create major challenges for realising $\textit{in situ}$ 2D characterisation quality control. Here, we have developed protocol enable inline uv-vis-nIR spectroscopy determine atomic layer number in-process.