Project VI: DNA migration in pressure-driven flow

In pressure driven flow in a channel, the polymers are stretched by the fluid velocity gradient. Polymers become stretched when flow shear rate > (relaxation time)^(-1).Due to the asymmetric streamlines around an extended polymer near the wall, the polymer is pushed away from the wall, leading to polymer depletion near the walls. The simulations agree well with the experiment in the prediction of the depletion layer thickness.

The depletion layer thickness dependes on the shear rate and polymer relaxation time. For a given shear rate, the longer polymer would have the longer relaxation time and the larger depletion layer thickness. The consequence being that longer polymers would have a higher average velocity than the shorter polymers, allowing separation of DNA molecules by length in microflow. [1,2]

[1] Y.-L. Chen, K. Jo, D.C. Schwartz, M.D. Graham, and J.J. de Pablo, Macromolecules, 38, 6680 (2005).

[2] K. Jo, Y.-L. Chen, J.J. de Pablo, D.C. Schwartz, Lab on a Chip, 9, 2348 (2009)