(262e) Dynamics of Thin Sheets in Stokes Flow: Stretching, Folding, and Exfoliation

The synthesis of 2D materials such as graphene and boron nitride usually requires a fluidic environment to achieve large-scale production. Those processes involve complicated fluid-structure interactions, such as folding and exfoliation, that have not been fully understood. We explore the aforementioned scenario by developing a continuum model of deformable sheets in extensional and shear flows. The model accounts for two aspects of mechanical responses: in-plane deformation and out-of-plane bending, and the fluid motion is computed using the method of regularized Stokeslets. In uniaxial extensional flow, we observed a phenomenon similar to the coil-stretch transition of chain-polymers. A deformable sheet modeled by a strain-softening model (neo-Hookean) approaches a singularity in length in the stretching direction, while a sheet with a strain-hardening model (Yeoh) can maintain the shape under large deformation. The stretching also induces interesting wrinkling and folding patterns depending on the deformability of the sheet; these affect the time-dependence and final degree of stretching of the sheet. In addition, we also explore the exfoliation behavior in shear flow by considering stacks of sheets that interact via van der Waals interaction. We observed the exfoliation in a two- or three-sheet model and characterized the exfoliation region in parameter space based on the deformability of the sheets.