Superhydrophobic, passive microvalves with controllable opening threshold: exploiting plasma nanotextured microfluidics for a programmable flow switchboard

Plasma processing is used to create passive superhydrophobic on-off valves with tailored opening pressure inside microfluidic devices. First, anisotropic O-2 plasma etching on polymeric microchannels is utilized to controllably roughen (nanotexture) the bottom of the microchannel. Second, the nanotextured surfaces are hydrophobized by means of a C4F8 plasma deposition step through a stencil mask creating superhydrophobic stripes or patches. The superhydrophobic patches play the role of on/off valves with predesigned opening pressure threshold (in the range 40-110 mbar), determined by the microchannel dimensions and the size of the nanotexture on the patch. These valves are integrated inside microchannel networks paving the way to autonomous microfluidic devices. To this aim, we present a novel preprogrammable flow switchboard that can split and control the liquid flow for multiple analysis purposes. The proposed valves present an example of how effectively plasma nanoscience and nanotechnology can be applied to microfluidics/nanofluidics and analytical chemistry.