Folding flakes: the deformation of elastic sheets in a viscous flow

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Two-dimensional materials are currently the subject of extensive research to harness their unique mechanical andelectrical properties for technological applications. Although much of their processing is performed in a liquid environment, e.g., during the size selection of dispersed graphene flakes by centrifugation or their deposition by ink-jet printing, their interaction with the surrounding fluid - which may result in folding, crumpling or even fracture and thus irremediably alter their physical properties - has not been characterised. Indeed, the large aspect ratio of graphene flakes implies that despite their impressive in-plane stiffness they have a very small bending stiffness and are therefore easily deformed by the traction that the surrounding fluid exerts on them. The aim of this project is to characterise the effect of fluid-structure interaction of these large aspect-ratio materials. Using quantitative experiments, we will study how deformation affects the sedimentation of thin elastic sheets - a simple fluid-structure configuration closely linked to centrifugation processes. We will assess how the flow-induced deformation affects the rate at which such sheets sediment; we will explore the effect of the sheets' aspect ratio (long and narrow sheets are likely to behave similarly to rod-like particles whose behaviour is much simpler and reasonably well understood); and determine how frustrated patterns observed in preliminary experiments emerge small-amplitude initial deformations.