Explicit- and Implicit-Solvent Molecular Dynamics Simulations of Complex Formation between Polycations and Polyanions

Abstract

Explicit- and implicit-solvent molecular dynamics simulations are performed to study complexation in two polyelectrolyte systems: poly(styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH) and poly(acrylic acid)/poly(allylamine hydrochloride) (PAA/PAH). Both these systems have been used in layer-by-layer assembly of polyelectrolyte films, with the first of these typically yielding linear growth in film thickness with increasing numbers of layers and the second yielding exponential growth. In both the systems, the polyelectrolytes have the same number of monomers and are present in stoichiometric proportion, and water is used as solvent. Simulations give important insights into the structure and composition of the complexes. We found that the PSS/PAH complex is more compact and has a smaller fraction of water than the PAA/PAH complex due to the presence of phenyl rings in the PSS chain and the hydrophilic nature of the charged group in the PAA chain. Either an increase in salt concentration or a decr...