We studied the influence of surface asperities on the interfacial flow of a liquid over a solid surface. As examples, we present three illustrative series of measurements:
(i)
drainage force between a hydrophobic flat surface and two hydrophobic colloidal particles
(ii)
drainage force between a hydrophilic flat surface and two hydrophilic colloidal particles
In both series, one particle had asperities and the other was relatively smooth
(iii)
drainage force between two hydrophilic flat surfaces patterned on different length scales and a smooth hydrophilic colloidal particle
For this third series, we show two representative experimental sets of force curves. We then compare the results with measurements on flat silicon surfaces.