Equilibrium properties of a grafted polyelectrolyte with explicit counterions

TL;DR

This study uses Monte Carlo simulations to explore how a grafted polyelectrolyte's conformation varies with electrostatic and attractive interactions, revealing complex phase transitions influenced by counterion binding.

Contribution

It provides a detailed phase diagram of polyelectrolyte conformations considering explicit counterions, highlighting reentrant behavior and shape fluctuations.

Findings

Conformations include extended, pearl, sausage, and globular states.

Transitions depend on Lennard-Jones attraction strength and electrostatic parameters.

Shape fluctuations are critical near the S-G transition.

Abstract

We study the equilibrium conformations of a grafted polyelectrolyte (PE) in the presence of explicit counterions (CI) using Monte Carlo simulations. The interplay between attractive Lennard-Jones interactions (parametrized by epsilon), and electrostatics (parametrized by A = q^2l_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 epsilon, we observe a transition from G -> P_2 -> P_3 -> . . . -> S -> G with increasing A, i.e., a change from poor to good, to reentrant 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.