(435h) Novel Model for Electrohydrodynamic Interactions of Polyelectrolytes.

Electric fields are commonly utilized to manipulate transport of polyelectrolyte molecules, such as DNA, in microfluidic devices. In addition to electrophoretic motion in the direction of an applied electric field, a polyelectrolyte molecule undergoes motion induced by electrohydrodynamic interactions (EHI), i.e. interactions due to disturbances in the fluid flow caused by motion of charged particles (polymer backbone and counterions) induced by the electric field. EHI can be utilized, for example, to concentrate polyelectrolytes within a microfluidic device by simultaneously applying electric and flow fields in the direction of a microfluidic channel [1,2]. In this case, local shear of the flow stretches and reorients a polyelectrolyte molecule so that EHI within the molecule lead to its transverse migration towards the center of the channel.

Modeling of EHI between different portions of a polyelectrolyte molecule remains a challenge due to a complex interplay between molecular configuration and electrohydrodynamic flows. Although current models [3-6] are in a qualitative agreement with experiments [1], they exhibit a substantial quantitative discrepancy with the experimental data at moderate and strong electric fields [7]. These models include contributions from long-range EHI [3], i.e. interactions between beads in a bead-and-spring polymer model and short-range EHI [4-6] due to electrohydrodynamic mobility of individual Kuhn steps comprising the springs. However, the current models do not properly account for medium range EHI, i.e. interactions between Kuhn steps within the springs.

In this talk, we present a medium-range model for EHI. In this model, Kuhn steps of a polymer chain are modeled as rigid rods and a slender body theory is developed to model EHI between them. We then perform Monte Carlo simulations of a spring comprised of rods to obtain contribution of the rod-rod interactions to electrohydrodynamic mobility of the spring. Thus obtained spring mobility is then utilized in Brownian dynamics simulations of a bead-and-spring polyelectrolyte model in external electric and flow fields. Results of these simulations are compared with experimental data [1] for concentration profiles of DNA molecules in microfluidic channels.

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

[3] R. Kekre, J. E. Butler, and A. J. C. Ladd, Phys. Rev. E, 82, 050803 (2010).

[4] W.-C. Liao, N. Watari, S. Wang, X. Hu, R. G. Larson, and L. J. Lee, Electrophoresis, 31, 2813–2821 (2010).

[5] H. Pandey and P. T. Underhill, Phys. Rev. E, 92(5), 052301 (2015).

[6] A. J. C. Ladd, Mol. Phys., 116, 3121–3133 (2018).

[7] D. Kopelevich, S. He, R. Montes, and J. E. Butler, J. Fluid Mech., 915, A59 (2021).