title: Detailed molecular dynamics simulations of a model NaPSS in water.
abstract: Hydrophobic polyelectrolytes are known to form necklace-like structures of dense beads connected by strings of monomers. This structure appears as a result of optimization of the electrostatic and short-range interactions. To elucidate the effect of counterion condensation and solvent on polyelectrolyte conformations, we performed two sets of molecular dynamics simulations of model poly(styrene)-co-styrene sodium sulfonate (NaPSS) chains with the degree of polymerization N = 16-64 and fraction of charged monomers f = 0.25-1 in aqueous solutions: (1) water molecules were considered explicitly using the TIP3P-PME model and (2) water molecules were modeled as a dielectric continuum with the dielectric constant 77.73. Our simulations showed that with increasing fraction of sulfonated groups f a polystyrene sulfonate chain adopts an elongated conformation. There is a transition between collapsed and elongated states which is manifested in the change of the scaling dependence of the chain size on the degree of polymerization. The effect of the water-ion interactions on counterion condensation was analyzed by comparing the radial distribution functions between the sulfonated groups and counterions for chains with different f values. In the case of the collapsed NaPSS chains, it was found that ionized groups are located at the globular surface.
authors.affiliation: Polymer Program, Institute of Materials Science and Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: Jan-Michael Y
authors.initials: JM
authors.lastname: Carrillo
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Dobrynin