1. Counterion Condensation and Collapse of Polyelectrolyte Chains
in a Poor Solvent: Computer Simulations and Theoretical Study
Andrey V. Dobrynin, Department of Physics, University of Connecticut
Polyelectrolytes are polymers with ionizable groups. In polar solvents with high dielectric constants these groups dissociate leaving charged groups on the polymer backbone and releasing counterions into solution. The static and dynamics properties of polyelectrolytes in solutions at surfaces strongly depend on the charge acquired by polyelectrolyte chains after dissociation process. The amount of the ionized groups is very sensitive to the solution dielectric constant, solvent quality for the polymer backbone, polymer and salt concentrations.
Using combination of the molecular dynamics simulations and scaling analysis we have studied the effect of the solvent quality for the polymer backbone, strength of the electrostatic interactions, chain degree of polymerization and brush grafting density on the conformations of planar polyelectrolyte brushes in salt-free solutions. Our simulations have shown that the polyelectrolyte brush could form: (1) hemispherical micellar aggregates, (2) vertically oriented cylindrical micelles, (3) maze-like aggregate structures, or (4) thin polymeric layer uniformly covering the substrate. These different brush morphologies appear as a result of the fine interplay between electrostatic and short-range monomer-monomer attractive interactions. The brush thickness shows nonmonotonic dependence on the value of the Bjerrum length determining the strength of the electrostatic interactions. It first increases with increasing the value of the Bjerrum length than begins to decrease. This behavior can be explained by counterion condensation within brush volume.