Regimes of electrostatic collapse of a highly charged polyelectrolyte in a poor solvent

AM Tom and S Vemparala and R Rajesh and NV Brilliantov, SOFT MATTER, 13, 1862-1872 (2017).

DOI: 10.1039/c6sm02152b

We perform extensive molecular dynamics simulations of a highly charged, collapsed, flexible polyelectrolyte chain in a poor solvent for the case when the electrostatic interactions, characterized by the reduced Bjerrum length l(B), are strong. We find the existence of several sub- regimes in the dependence of the gyration radius of the chain R-g on l(B) characterized by R-g similar to l(B)(-gamma). In contrast to a good solvent, the exponent gamma for a poor solvent crucially depends on the size and valency of the counterions. To explain the different sub- regimes, we generalize the existing counterion fluctuation theory by including a more complete account of all possible volume interactions in the free energy of the polyelectrolyte chain. We also show that the presence of condensed counterions modifies the effective attraction among the chain monomers and modulates the sign of the second virial coefficient under poor solvent conditions.

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