Elastic secondary flows of semidilute DNA solutions in abrupt 90 degrees microbends.

Secondary flows that are absent in Newtonian flows are found for semidilute lambda -DNA solutions in abrupt planar 90 degrees microbends at modest levels of elasticity. Flow visualization and microparticle image velocimetry experiments show that a vortex, which is present in the inner, upstream corner of the bend, grows with increasing Reynolds and Weissenberg number (9.9x10;{-7}<Re<3.1x10;{-2},0.41<Wi<126) . The vortex growth is quantified as a function of elasticity; at high elasticity, the vortex occupies a significant fraction of the upstream channel and distorts the primary flow. The presence of elastic vortices, in which molecules can become trapped for long times, has implications for the design of microdevices for the processing of biological macromolecules.