Wednesday, May 1, 2013

1304.8098 (Marcello Sega et al.)

Water slippage on non-ideal surfaces: the role of static and dynamic

Marcello Sega, Mauro Sbragaglia, Luca Biferale, Sauro Succi
We present non-equilibrium Molecular Dynamics simulations of water flow in nano-channels with the aim of discriminating static from dynamic contributions of the wall atoms to the slip length of the molecular flow. To this purpose, we vary the rigidity of model springs and the mass of the tethered wall molecules independently, so as to separately tune the rugosity and the flexibility of the walls. First, it is found that the slip length for small to moderate values of the shear intensity is significantly enhanced by increasing the wall flexibility. Second, and perhaps more importantly, we show that the regularization of the slip length divergence at high shear rates, formerly attributed to wall flexibility, is controlled only by the static surface roughness. Minimal displacements, caused for example by thermal motion at room temperature, are shown to be sufficient to remove the aforementioned divergence.
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