Phase diagram of flexible polymers with quenched disordered charged monomers

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 (77). The coil-globule and globular-solid transitions are second and first order for the entire concentration range. However, above a concentration threshold of 77 = 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 77, 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 77.

Automated summary

Recent advances in Generalized Ensemble simulations and microcanonical analysis have shown the significant role of electrostatic interactions in structural transitions of polymer models. In this study, a bead-spring polymer model with randomly distributed charged monomers interacting via a screened Coulomb potential was proposed. It was found that the coil-globule and globular-solid transitions were second and first order for the entire concentration range. However, above a concentration threshold of 80%, the electrostatic repulsion hindered the formation of solid and liquid globules, leading to the formation of liquid pearl-necklace and solid helical structures instead.