Interfacial Flow Visualization in Microfluidic Channels

Study of capillary driven flow is important in microfluidic devices. Capillary driven flows are often accompanied by formation of interface between phases of fluid participating in the flow. Interfacial flow visualization becomes necessary for tracking the transient flow in the microfluidic devices. A novel method for visualization of the meniscus interface using a standard micro particle image velocimetry (micro-PIV) apparatus is presented in this paper. The modifications carried out in the existing micro-PIV apparatus for interface tracking is described. Test samples of microfluidic channels made of glass and polydimethylsiloxane (PDMS) with different geometrical dimensions are visualized and reported. Different test fluids like DI water, isopropyl alcohol have been used in the microchannels. The parameters such as optical properties of the test sample and physical properties of the test fluid influence greatly on the resolution of the interface images. Open channel microfluidic study is also done by studying the interface phenomena of an evaporating droplet on a PDMS microchannel. The effect of the surface properties on the visualization of the evolution of the meniscus interface is emphasized. The intent of the study is to demonstrate and show how the versatility of micro-PIV can be extended for interfacial flow visualization.