Lattice Boltzmann simulations in microfluidics: probing the boundary condition

In this contribution we summarize our investigations of the effect of boundary slip by utilizing lattice Boltzmann simulations. We investigate fluid flow in hydrophobic and rough microchannels and show that a slip due to hydrophobic interactions increases with increasing hydrophobicity and is independent on the shear rate. If surface roughness is not treated properly while analysing experimental results, a large apparent slip might be measured. We show that the no-slip boundary condition holds in this case if an effective surface position at an intermediate position between peaks and valleys of the surface is considered. Further, we study the effect of microbubbles present on a surface and show that gas bubbles can have a strong impact on the flow properties. They can cause negative slip and due to their deformability, a shear rate dependent slip might be detected in experiments