Dynamics of Capillary-Driven Flow in Open Microchannels

The dynamics of capillary-driven flow was studied for water and water-glycerol mixtures in open hydrophilic microchannels (embedded in a hydrophobic matrix). The position of the advancing meniscus was recorded as a function of time using high speed microscopy and compared with the Washburn equation. The square of the position of the liquid front increased linearly with time, as predicted by Washburn. For a channel of the same depth, irrespective of the shape of the channel cross-section (rectangular or curved), the liquid flow was faster with decreasing channel width. A modified Washburn equation, accounting for the different flow profile in the open, noncylindrical channels, was developed. The theoretical prediction was in good agreement with the experimental data for a no-slip boundary condition at the liquid-air interface.