Phase diagram of flexible polymers with quenched disordered charged monomers

Abstract

Recent advances in Generalized Ensemble simulations and microcanonical analysis allowed the investigation of structural transitions in polymer models over a broad range of local bending and torsion strengths. It is reasonable to argue that electrostatic interactions play a significant role in stabilizing and mediating structural transitions in polymers. We propose a bead–spring polymer model with randomly distributed charged monomers interacting via a screened Coulomb potential. By combining the Replica Exchange Wang–Landau (REWL) method with energy-dependent monomer updates, we constructed the hyperphase diagram as a function of temperature (T) and charged monomer concentration (η). The coil–globule and globular–solid transitions are second and first order for the entire concentration range. However, above a concentration threshold of η=80%, electrostatic repulsion hinders the formation of solid and liquid globules, and the interplay between enthalpic and entropic interactions leads to the formation of liquid pearl-necklace and solid helical structures. The probability distribution, P(E,T), indicates that at high η, the pearl-necklace liquid phase freezes into a stable solid helix-like structure with a free energy barrier higher than the freezing globule transition at low η.