There has been significant progress in developing coarse-graining methods, but most are limited to equilibrium systems. The talk will describe two different approaches for nonequilibrium systems with applications to electroosmotic transport and yield of glassy polymers. Electroosmotic transport in micro-and nano- channels has important applications in biological and engineering systems. The driving force is proportional to the charge density, which is largely confined to the bounding walls and sensitive to the atomistic structure of solvent and ions. We describe an efficient hybrid multiscale method for simulating nano-scale electroosmotic flow based on spatial domain decomposition. Molecular dynamics (MD) is used in the near wall region where atomistic details are important. Away from the walls, a discrete description of ions is retained because of the low density of ions and the long-range of electrostatic interactions. Ions interact with an implicit solvent obeying the incompressible Navier-Stokes equations. The fully atomistic and continuum descriptions are coupled through constrained dynamics in an overlap region that ensures continuity of ion and solvent flux. This hybrid approach is tested against pure MD simulations and used to examine the large effect of wall roughness and fluid structure at atomic scales on electroosmotic flow.Simulating shear flow of glassy polymers poses a greater challenge because systems sample very different atomic configurations than the equilibrium ensembles used to generate most coarse-grained potentials. We first compare simulations of sheared polystyrene using atomistic and coarse-grained potentials. While the coarse-grained potential reproduces conformational changes in individual molecules and qualitative features of the stress-strain curves, the yield stress is a factor of five lower. The origins of this large discrepancy and methods to reconstruct stress-strain curves using alternating fine and coarse grained simulations will be described.Supported by NSF Grant No. DMR-1006805 and ARL/JHU Cooperative Agreement W911NS-12-2-0022.

Coarse-graining for nonequilibrium simulations: Electroosmosis and yield

246th National Meeting (2013)

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