Coarse-grained explicit-solvent molecular dynamics simulations of semidilute unentangled polyelectrolyte solutions

Journal Article · Thu Oct 05 00:00:00 EDT 2023 · European Physical Journal. E, Soft Matter (print)

DOI:https://doi.org/10.1140/epje/s10189-023-00342-2· OSTI ID:2076188

Carrillo, Jan-Michael  ^[1]; Wang, Yangyang  ^[1]; Kumar, Rajeev  ^[1]; Sumpter, Bobby G.  ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)

In this study, we present results from explicit-solvent coarse-grained molecular dynamics (MD) simulations of fully charged, salt-free, and unentangled polyelectrolytes in semidilute solutions. The inclusion of a polar solvent in the model allows for a more physical representation of these solutions at concentrations, where the assumptions of a continuum dielectric medium and screened hydrodynamics break down. The collective dynamic structure factor of polyelectrolytes, S(q, t), showed that at q > q*, where q* = 2π/ξ is the polyelectrolyte peak in the structure factor S(q) and ξ is the correlation length, the relaxation time obtained from fits to stretched exponential was ^$$\tau$$KWW ~ q^-3, which describes unscreened Zimm-like dynamics. This is in contrast to implicit-solvent simulations using a Langevin thermostat where ^$$\tau$$KWW ~ q^-2. At q < q*, a crossover region was observed that eventually transitions to another inflection point ^$$\tau$$KWW ~ q^-2 at length scales larger than ξ for both implicit- and explicit-solvent simulations. The simulation results were also compared to scaling predictions for correlation length, ξ ~ c$$-½\atop{p}$$, specific viscosity, η_sp ~ c$$½\atop{p}$$, and diffusion coefficient, D ~ c$$0\atop{p}$$, where c_p is the polyelectrolyte concentration. The scaling prediction for ξ holds; however, deviations from the predictions for η_sp and D were observed for systems at higher c_p, which are in qualitative agreements with recent experimental results. This study highlights the importance of explicit-solvent effects in molecular dynamics simulations, particularly in semidilute solutions, for a better understanding of polyelectrolyte solution behavior.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725; KC0402010
• OSTI ID: 2076188
• Journal Information: European Physical Journal. E, Soft Matter (print), Vol. 46, Issue 10; ISSN 1292-8941
• Publisher: EDP Sciences
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
polyelectrolytes
semidilute solutions
molecular dynamics
simulations