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 (CI) usingMonte Carlo simulations. The interplay between attractive Lennard- Jones interactions (parametrized by ε), and electrostatics (parametrized by A = q²l_B/a, where q =counterion valency, l_B = Bjerrum length and a = monomer diameter), results in a variety of conformations, characterized as extended (E), pearls with m beads (P_m), 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.