Two-phase flow in microchannels with surface modifications

Two-phase flows in microchannels with surface modifications are experimentally investigated. First, we investigate the shape of static and moving bubbles in microchannels with square cross-sections for different contact angles. Water and air are mixed on-chip in a cross-shaped mixing chamber. This mixing geometry allows for the production of monodisperse bubbles, the size of which can be controlled with the flow rates. We study the flow morphologies of mixtures made of pure water and air, and made of water with surfactant and air (aqueous foam), in both hydrophilic and hydrophobic microchannels. Second, we investigate the transient theological behavior of polymer solutions when the length of the polymers is comparable to the height of the channel. The measured viscosity of the solution is several times larger than the expected value, and does not show the typical shear-thinning behavior. These experiments highlight the importance of wall properties for two-phase flows in microfluidic devices. (c) 2006 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.