Equilibrium properties of a grafted polyelectrolyte with explicit counterions

Abstract

We study the equilibrium conformations of a grafted polyelectrolyte (PE) in the presence of explicit counterions (CIs) using Monte Carlo simulations. The interplay between attractive Lennard-Jones interactions (parametrized by epsilon) and electrostatics (parametrized by A=q2lB/a, where q is the CI valency, lB is the Bjerrum length, and a is the monomer diameter) results in a variety of conformations, characterized as extended (E), pearls with m beads (Pm), sausage (S), and globular (G). For large epsilon, we observe a transition from G-->P2-->P3-->…-->S-->G with increasing A, i.e., a change from poor to good, to re-entrant poor solvent, whereas, at lower epsilon, the sequence of transitions is E-->S-->G. The conformation changes are directly related to the nature of binding of CI onto the PE. The transition between S-->G is continuous and associated with critical fluctuations in the shape driven by fluctuations in the fraction of condensed CI. ©2009 American Institute of Physics