Plasma processing for polymeric microfluidics fabrication and surface modification: Effect of super-hydrophobic walls on electroosmotic flow

We report on the fabrication and electrokinetic characterization of poly-methyl methacrylate (PMMA) microfluidics by deep O2 plasma etching, utilizing a photosensitive poly-(dimethyl siloxane) (PDMS) as a resist (in situ mask). The mass production amenability, the high throughput without the use of mold, the dry character along with the flexibility to control surface properties towards specific demands are some of the advantages of this method. Intense ion bombardment ensures high etch rates (∼1.5 μm/min) and anisotropy. A PMMA lid was thermally bonded to the plasma fabricated microchannel under 1.8 kg/cm2 at 120 °C. Surface roughness and hydrophilization are some unique features induced by plasma processing, affecting the electrokinetic performance of the microfluidic and resulting in relatively high electroosmotic flow (EOF) mobilities of 2.83 × 10−4 cm2/V s. Teflon-like coating deposition on the engraved part modified the surface into a super-hydrophobic and resulted in even higher EOF mobility (3.89 × 10−4 cm2/V s), thus proposing an alternative means in microfluidic surface modification and EOF control.