Mixing Immiscible Fluids in a Microchannel Through Surface Modifications

We present a fluidic concept for the guiding of two immiscible solvents through a PMMA- micro channel only by means of surface forces. The liquids do not flow in parallel through the channel, but cross each other, induced by spatial variations of the surface chemistry. This leads to a temporary mixing of the fluids, followed by separation like in a macroscopic separatory funnel. The surface modification is prepared by thin films of statistical copolymers composed of either acrylic acid as hydrophilic or n-butyl acrylate as hydrophobic polymer and a photo reactive monomer. UV illumination simultaneously cross-links and chemically links the layer to the cover surface. The thus modified cover is then solvent bonded to the microfluidic chip.