Equilibrium properties of a grafted polyelectrolyte with explicit counterions

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 ε) and electrostatics (parametrized by A= q2 lB /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 ε, 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 ε, 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.