Modulating passive micromixing in 2-D microfluidic devices via discontinuities in surface energy

Passive mixing can be induced on the micron length scale in a surface tension-confined microfluidic device through the modulation of surface energy by the direct patterning of a hydrophilic material upon an otherwise hydrophobic substrate. The advancing meniscus of a capillary-driven fluid accelerates and decelerates as it comes into contact with the regions of disparate surface energy creating a ‘weaving’ trajectory across the virtual microchannel resulting in horizontal and vertical lamination. The efficacy of this technique was demonstrated utilizing image analysis and Shannon entropy. Additionally, a neutralization reaction exhibited the ability of hydrophilic/hydrophobic interactions to efficiently homogenize and facilitate on-chip reactions in spite of the absence of traditional micromixing strategies. Such results suggest that this inexpensive and autonomous micromixing technique may effectively support reaction processes for portable sensor applications.