(492h) Coupling between Internal Dynamics and Transport of Polyelectrolytes in External Electric and Flow Fields

Electric fields are commonly utilized to manipulate macromolecular transport within microfluidic devices for analysis and processing. In particular, simultaneous application of axial electric and flow fields within a microfluidic channel containing polyelectrolyte molecules, such as DNA, can drive transverse migration of polyelectrolytes [1]. This transverse motion has been used to trap and concentrate polyelectrolytes within microfluidic devices and has even been used to separate long and flexible polyelectrolytes from other molecules [2].

The transverse migration is caused by electrohydrodynamic interactions between different portions of the polymer molecule, i.e. interactions due to disturbances in the fluid flow caused by motion of charged particles (polymer backbone and counterions), which in turn are induced by an external electric field. Transport of polyelectrolytes induced by electrohydrodynamic interactions is closely related to their conformation. For example, the transverse migration in an external electric field requires that the polymer is stretched and tilted by an external fluid flow. In addition, as a polyelectrolyte molecule undergoes thermal fluctuations, each of its configurations corresponds to a different instantaneous electrohydrodynamic velocity and these velocity fluctuations contribute to diffusive motion referred to as the electrohydrodynamic dispersion. It was recently shown [3,4] that the electrohydrodynamic dispersion is a key factor in determining efficiency of polyelectrolyte trapping in microfluidic devices

In this talk we discuss relation between internal dynamics of a polyelectrolyte molecule and its transport properties (migration and dispersion). The electrohydrodynamic interactions substantially alter the polymer dynamics so that the standard models for dynamics of electrically neutral polymers (such as the Rouse model) are not adequate. We modify the Rouse model and use nonlinear principal component analysis to identify dominant modes for polyelectrolyte dynamics. These modes are then related to the migration and dispersion of polyelectrolytes. The developed theory is in quantitative agreement with Brownian dynamics simulations and in qualitative agreement with experiment.

1. M. Arca, J. E. Butler and A. J. C. Ladd, Soft Matter, 11, 4375–4382 (2015).

2. B. E. Valley, A. D. Crowell, J. E. Butler, and A. J. C. Ladd, Analyst 145, 5532–5538 (2020).

3. D. I. Kopelevich, S. He, R. Montes, and J. E. Butler, J. Fluid Mech., 915, A59 (2021).

4. D. I. Kopelevich and J. E. Butler, Phys. Rev. Fluids, 6, 094203 (2021).