Marangoni flow in a microchannel

This paper describes the experimental results of Marangoni flow in a microchannel. The microchannel that we examined was made of polydimethylsiloxane (PDMS), shaped by photolithography and molding techniques. The typical channel size was about 100 μm width and 55-70 μm hight. A single-component liquid with ethanol and two-component liquids with mixtures of ethanol and distilled water were used as test liquids. Both liquids contained 1-5 μm diameter tracer particles to visualize the flow-field. Velocity distribution for the single-component liquid shows a fountain-like flow under the reference frame of the gas-liquid interface position. In stark contrast, the distribution for the two-component liquids shows a strong rolling motion near the interface caused by Marangoni flow resulting from a concentration difference. In most cases, this rolling motion is symmetrical to the central axis of the channel. On the interface, the liquid flows from the center to the edge (contact line) position, and the velocity is independent of interfacial velocity and direction. In some cases, we found asymmetric rolling motion. To observe this phenomenon more precisely, we are developing a 3-dimensional (3-D) flow observation system. The flow structures are discussed with the 3-D observation. This phenomenon seems to offer large capability for microfluidic applications such as in a micromixer.