Shape of the liquid-liquid interface in micro counter-current flows.

We investigated the shape of the liquid–liquid interface in micro counter-current flows formed within microchannels. The pressure balance at the interface was calculated based on the interface geometry. Although the shape should be an arc under laminar flow, a large deformation near the center of the microchannel was observed. In the center of the microchannel, Laplace pressure (171 – 450 Pa) was induced toward the aqueous phase. In contrast, near both sidewalls, Laplace pressure (81 – 166 Pa) was induced toward the organic phase. This result suggests that opposing flow occurs in the adjacent phases near the interface, with spiral-like flow generation.