Conformational Properties of Comb-Like Polyelectrolytes: A Coarse- Grained MD Study
M Ghelichi and MH Eikerling, JOURNAL OF PHYSICAL CHEMISTRY B, 120, 2859-2867 (2016).
This article presents a coarse-grained molecular dynamics study of single comb-like polyelectrolyte or ionomer chains in aqueous solution. The model polymer is comprised of a hydrophobic backbone chain with grafted side chains that terminate in anionic headgroups. The comb- polymer is modeled at a coarse grained level with implicit treatment of the solvent. The computational study rationalizes conformational properties of the backbone chain and localization of counterions as functions of side chain length, grafting density of side chains, backbone stiffness, and counterion valence. The main interplay that determines the ionomer properties unfolds between electrostatic interactions among charged groups, hydrophobic backbone interactions, and steric effects induced by the pendant side chains. Depending on the density of branching sites, we have found two opposing effects of side chain length on the backbone gyration radius and local persistence length. Variation in comb polyelectrolyte architecture is shown to have nontrivial effects on the localization of mobile counterions. Changes in Bjerrum length and counterion valence are also shown to alter the strength of Coulomb interactions and emphasize the role of excluded- volume effects on controlling the backbone conformational behavior. The results of simulations are in qualitative agreement with existing experimental and theoretical studies. The comprehensive conformational picture provides a framework for future studies of comb polyelectrolyte systems.
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