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. (C) 2009 Elsevier B.V. All rights reserved.