Simulation of fluid flow in hydrophobic rough microchannels

Abstract

Surface effects become important in microfluidic setups because the surface to volume ratio becomes large. In such setups the surface roughness is not any longer small compared to the length scale of the system and the wetting properties of the wall have an important influence on the flow. However, the knowledge about the interplay of surface roughness and hydrophobic fluid–surface interaction is still very limited because these properties cannot be decoupled easily in experiments.

We investigate the problem by means of lattice Boltzmann (LB) simulations of rough microchannels with a tunable fluid–wall interaction. We introduce an ‘effective no-slip plane’ at an intermediate position between peaks and valleys of the surface and observe how the position of the wall may change due to surface roughness and hydrophobic interactions.

We find that the position of the effective wall, in the case of a Gaussian distributed roughness, depends linearly on the width of the distribution. Further, we are able to show that roughness creates a nonlinear effect on the slip length for hydrophobic boundaries.

Keywords:

• lattice Boltzmann
• microflows
• apparent slip
• roughness
• hydrophobic fluid-surface interaction

Acknowledgements

We thank H. Gong for the AFM data and O.I. Vinogradova and M. Rauscher for fruitful discussions. This work was financed within the DFG priority program ‘nano- and microfluidics’ and by the ‘Landesstiftung Baden-Württemberg’. Computations were performed at the Neumann Institute for Computing, Jülich and at the Scientific Supercomputing Center, Karlsruhe.