(590i) Mesoscopic Models for Electro-Hydrodynamic Interactions of Polyelectrolytes

Modeling of polyelectrolytes in simultaneous external shear and electric fields represents a challenge due to a complex interplay between polymer configuration, hydrodynamic interactions, flows of counterions, and other factors. In this talk we compare two mesoscopic models for polyelectrolytes with experimental observations. Both models are based on a bead-and-spring representation of polyelectrolyte molecules but use qualitatively different approaches to modeling electro-hydrodynamic (EHI) interactions. One of these models approximates beads as spherical blobs of uniformly distributed point charges, which results in long-range interactions between the beads [1]. In contrast, the second model contains only short-range EHI interactions [2-4]. Within this model, the EHI-induced bead migration is calculated assuming that the interactions are localized to individual Kuhn steps which are modeled as slender bodies.

These models are utilized in a series of Brownian dynamics (BD) simulations of a polyelectrolyte in an external electric field and a pressure-driven flow applied in the same direction. Both EHI models qualitatively reproduce experimental observations [5]. Specifically, it is observed that a combination of the shear and electric fields leads to the polyelectrolyte drift in the direction transversal to the flow and electric field direction, which in turn leads to concentration of the polyelectrolyte in the center of a microfluidic channel. Furthermore, both EHI models predict that there is an optimal strength of electric field that leads to the most narrow distribution profile of the polyelectrolyte in the center of the channel. However, there is a quantitative disagreement between the BD results and the experimental data, which indicates that further progress in the model development is needed. In conclusion of the talk, we discuss potential improvements to the EHI models.

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

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

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

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

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