Necklace Globule and Counterion Condensation

Abstract

We have developed a necklace model of polyelectrolyte chain in which the necklace structure appears as a result of the counterion condensation on the polyelectrolyte backbone. This necklace structure optimizes the correlation-induced attraction of the condensed counterions and charged monomers and electrostatic repulsion between uncompensated charges. The new feature of this necklace globule is that it can be formed even in good solvent conditions for the polymer backbone. By using the scaling analysis, we have calculated the diagram of state of polyelectrolyte chain as a function of the solvent quality for the polymer backbone and value of the Bjerrum length. To test the predictions of a scaling model, we have performed molecular dynamics simulations of polyelectrolyte chains with the degrees of polymerizations N = 124−304 and fraction of charged monomers f = 1/3 in good, θ, and poor solvent conditions for the polymer backbone. We have identified the range of parameters in which the necklace globule is formed due to correlation-induced attractive interactions in the good solvent conditions for the polymer backbone. The results of the molecular dynamics simulations are in qualitative agreement with the predictions of a scaling model.

Does Electrical Conductivity of Linear Polyelectrolytes in Aqueous Solutions Follow the Dynamic Scaling Laws? A Critical Review and a Summary of the Key Relations

“…These different regimes imply a different picture of counterion condensation, which will condense on the necklace globule in an avalanche-like fashion. As pointed out by Jeon and Dobrynin [39], with the increase of the polyion concentration, counterions condense inside beads of the necklace globule, favoring the reduction of its charge and the increase of its mass which further promote the counterion condensation giving rise to the avalanche-like process. The necklace conformation is supported by experiments [40] and computer simulations [41,42].…”

Salt Effect on Osmotic Pressure of Polyelectrolyte Solutions: Simulation Study

“…The addition of the multivalent salts [40][41][42] and changes in solvent quality for the polymer backbone [43][44][45][46] can modify chain conformations. We are planning to consider how these effects will influence solution osmotic pressure in future publications.…”

Communication: Intraparticle segregation of structurally homogeneous polyelectrolyte microgels caused by long-range Coulomb repulsion

“…The solvent quality is quantified by the Lennard-Jones intermonomer interaction parameter ε LJ which is varied between 0.01 (good solvent) and 1 k B T (poor solvent). The value of the Lennard-Jones parameter for monomer-counterion and counterion-counterion interactions was set to 1 k B T. 23,24 Electrostatic interactions between any pair of charged particles are described by Coulomb potential. The value of the Bjerrum length was fixed and equal to l B = 3σ, which corresponds to aqueous solutions.…”