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Published May 24, 2022 | Supplemental Material
Journal Article Open

Complexation between Oppositely Charged Polyelectrolytes in Dilute Solution: Effects of Charge Asymmetry


We use dissipative particle dynamics to study polyelectrolyte complexation in dilute solutions under conditions of either chain-length or concentration asymmetry between the polycation and the polyanion, characterized by the macromolecular charge ratio of the minor component to the major component. Our results show that generally the systems form clusters carrying net macromolecular charges. The stoichiometry of these net-charged macromolecular clusters depends on the overall charge asymmetry, and clusters with certain stoichiometry can dominate the cluster population under a wide range of chain-length and concentration asymmetry. The morphology and stability of these net-charged clusters are closely related to their stoichiometry. When the charge ratio reaches a threshold value, the polyions condense into a single large coacervate cluster, signaling the onset of macroscopic coacervation. The threshold value is less for concentration asymmetry systems than for chain-length asymmetry systems at the same salt concentration. This threshold value decreases with added salt, as salt ions cause merging of small clusters into larger ones, eventually leading to the dominance of a single large cluster. This "salting-out" phenomenon is followed by a "salting-in" behavior, as further addition of salt dissolves the large cluster. The preferred size and composition of the net-charged clusters observed in the simulation highlight the significant role of length and concentration asymmetry on polyelectrolyte complex coacervation and hint at the possibility of a microstructured liquid.

Additional Information

© 2022 American Chemical Society. Received: February 15, 2022; Revised: April 23, 2022; Published: May 13, 2022. This research was supported by funding from Hong Kong Quantum AI Lab Ltd. This research used resources of the Center for Functional Nanomaterials (CFN), which is a U.S. Department of Energy Office of Science User Facility, at Brookhaven National Laboratory under Contract DE-SC0012704. P.Z. acknowledges the financial support provided by the National Natural Science Foundation of China (22073016 and 21803011) and the award of Shanghai Dongfang Scholar. The authors declare no competing financial interest.

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August 22, 2023
October 24, 2023