Shape and Diffusion of Circular Polyelectrolytes in Salt-Free Dilute Solutions and Comparison with Linear Polyelectrolytes

5 years ago

Shape and Diffusion of Circular Polyelectrolytes in Salt-Free Dilute Solutions and Comparison with Linear Polyelectrolytes

Lijun Liu, Wenduo Chen, Jizhong Chen

The shape and diffusion of circular polyelectrolytes in salt-free dilute solutions are investigated over a large range of the Bjerrum length l_B by mesoscale hydrodynamic simulations, where l_B characterizes the strength of electrostatic interactions (EIs). A comprehensive comparison of linear and circular polyelectrolytes is also made to gain a deep understanding of the effects of topological constraints on the conformational and dynamical properties. As l_B increases, counterions become increasingly important due to their condensations on the polyelectrolyte backbone. The shape of a circular polyelectrolyte changes from a prolate coil to an oblate ring at small l_B, then to a prolate coil at intermediate l_B, and finally to a dense coil at large l_B; in contrast, the shape of a linear polyelectrolyte changes from a prolate coil to a rod, then to a prolate coil, and finally to a dense coil. By switching on/off hydrodynamic interactions (HIs), the simulations clarify the complex coupling effects of hydrodynamic and electrostatic interactions on the diffusion of polyelectrolytes. With increasing l_B, the diffusion coefficient with HIs decreases rapidly and then increases gradually, but the diffusion coefficient without HIs displays an almost monotonically decreasing behavior and eventually approaches a plateau. The significant, quantitative but not qualitative difference in diffusion coefficient in the presence of HIs is found between linear and circular polyelectrolytes with an identical chain length, but there are only slight differences between their diffusion coefficients in the absence of HIs. By exploitation of the changes in chain size and the number of condensed counterions, we show that the diffusion of polyelectrolytes can be still qualitatively understood within the framework of Zimm and Rouse models.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b00189

DOI: 10.1021/acs.macromol.7b00189