Polymer chain conformation in polyelectrolyte complexes

The Complexation of oppositely charged polyelectrolytes through electrostatic interaction is ubiquitous in both natural and synthetic systems. One of the microscopic properties of interest in polyelectrolyte complexes (PEC) is the polymer chain conformation of a labeled chain. Recent literature studies on polycation/polyanion chain conformation in PEC’s using small-angle neutron scattering reported Gaussian chain statistics. Such scaling behavior is unlike polymer chains dissolved in good solvents, which show Gaussian statistics only at very high polymer concentrations (semidilute state). This behavior appears to be independent of chain length, salt concentration, and polymer concentration. We performed coarse-grained Langevin dynamics simulations of symmetric and flexible PECs and counterions, with and without salt added. As we gradually increase polymer concentration, the polymer chains transition from a globule-like state and level off to a Gaussian chain conformation. Qualitatively, similar behavior was also observed in the presence of salt. The polycations and polyanions have been observed to be highly overlapped in both cases. Such a qualitative agreement with experiments is observed because of the strong electrostatic driving force for complexation.