title: Flow of DNA solutions in a microfluidic gradual contraction.
abstract: The flow of λ-DNA solutions in a gradual micro-contraction was investigated using direct measurement techniques. The effects on DNA transport in microscale flows are significant because the flow behavior is influenced by macromolecular conformations, both viscous and elastic forces dominate inertial forces at this length scale, and the fully extended length of the molecule approaches the characteristic channel length wc (L/wc ∼ 0.13). This study examines the flow of semi-dilute and entangled DNA solutions in a gradual planar micro-contraction for low Reynolds numbers (3.7 × 10(-6 )< Re < 3.1 × 10(-1)) and high Weissenberg numbers (0.4 < Wi < 446). The semi-dilute DNA solutions have modest elasticity number, El = Wi/Re = 55, and do not exhibit viscoelastic behavior. For the entangled DNA solutions, we access high elasticity numbers (7.9 × 10(3 )< El < 6.0 × 10(5)). Video microscopy and streak images of entangled DNA solution flow reveal highly elastic behavior evidenced by the presence of large, stable vortices symmetric about the centerline and upstream of the channel entrance. Micro-particle image velocimetry measurements are used to obtain high resolution, quantitative velocity measurements of the vortex growth in this micro-contraction flow. These direct measurements provide a deeper understanding of the underlying physics of macromolecular transport in microfluidic flow, which will enable the realization of enhanced designs of lab-on-a-chip systems.
authors.affiliation: Bioengineering Program, School of Engineering and Computer Science, University of the Pacific , Stockton, California 95211, USA.
authors.forename: Shelly
authors.initials: S
authors.lastname: Gulati
authors.affiliation: Department of Chemical Engineering, University of California , Berkeley, California 94720, USA.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Muller
authors.affiliation: Department of Bioengineering, University of California , Berkeley, California 94720, USA.
authors.forename: Dorian
authors.initials: D
authors.lastname: Liepmann