(443e) Electrically Induced Hydrodynamic Interactions in Capillary Electrophoresis of Polyelectrolytes

An electric field acting on a charged polymer and its counter-ion cloud can create a net velocity field at long ranges, though observing the phenomena requires that the polyelectolyte configuration be distorted from equilibrium. Hydrodynamic effects in electric fields are usually claimed to decay exponentially on a length scales proportional to the Debye screening length (κ^-1). However, the disturbance velocity in an electric field decays algebraically over the a distance r, with a leading order term of (κ²r³)^-1. These electrically induced hydrodynamic interactions have been postulated to be responsible for the net transverse migration of DNA during transport through a capillary tube when both an electric field and pressure gradient are present [1].

Experiments have been conducted to test the hypothesis by measuring the migration of DNA when simultaneously applied an electric field and pressure gradient in parallel directions in a capillary. The shearing flow, created by the pressure gradient, acts to distort the DNA from its equilibrium configuration. Then, the hydrodynamic disturbances created by the electric field drive the migration. The extent of migration is measured as a function of electric field, flow strength, and Debye length, where the latter parameter is varied by changing the ionic concentration of the solution. The measured extent of migration is compared to the scaling predicted by the kinetic theory [1] and also to the results of Brownian dynamics simulations [2]. The results support the idea that velocity disturbances due to electrically induced hydrodynamic interactions exist and can have measurable influence on the dynamics of polyelectrolytes.

[1] J. E. Butler, O. B. Usta, R. Kekre and A. J. C. Ladd. Kinetic theory of a confined polymer driven by an external force and pressure-driven flow. Phys. Fluids, 19:113101, 2007.

[2] R. Kekre, J. E. Butler, and A. J. C. Ladd Role of hydrodynamic interactions in the migration of polyelectrolytes driven by a pressure gradient and an electric field. Phys. Rev. E, 82:050803(R), 2010