(290c) Coupled Atomistic-Continuum Model for Lubricated Flexible Membranes

Flexible membranes lubricated by a thin fluid layer are known to present interesting problems in classical fluid dynamics. Interactions between the fluid and the membrane tend to be important, even as the dimensions of the fluid gap becomes vanishingly small compared to the long-scale, leading to significant simplifications in the fluid mechanics. At the smallest length-scales however, Knudsen numbers are large so that the continuum approximations no longer hold and the atomic description becomes more appropriate. This, in effect, poses a multi-scale problem involving different treatment methods under different length-scales. In this study, we employ molecular dynamics (MD) to resolve regions where the continuum assumption breaks down and the Navier-Stokes (NS) equations to expedite calculations in the bulk region where molecular details could be neglected. Constraint particle dynamics are used in the intervening zone where MD and NS regions overlap. Using test-problems involving lubricated membranes, we show how flexible membranes interact with fluid at the nano-scale. The present study could be extended to biological problems involving attachment of lipid bilayers to substrates during cell attachment, or mechanical problems involving nano-valves and actuators.