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Published October 28, 2018 | Published + Supplemental Material
Journal Article Open

Polyelectrolyte complex coacervation: Effects of concentration asymmetry


Using a simple liquid-state theory, we study the phase behaviors of concentration-asymmetric mixtures of polycation and polyanion solutions. We construct a three-dimensional (3D) phase diagram in terms of the concentrations of the three independent charged components: polycation, polyanion, and small cation (p_(P^+) − p_(P^−) − p_+), for a given Bjerrum length. This phase diagram yields rich and complex phase-separation scenarios. To illustrate, we sequentially examine the following three systems that are directly relevant to experiments: a symmetric mixture, an asymmetric mixture with one type of small ions, and an asymmetric mixture with both types of small ions. We re-express the information in the 3D phase diagram using three experimentally more easily controllable parameters—the asymmetry factor r, the initial extra-salt concentration p_(s,0), and the initial polyelectrolyte (PE) concentration p_(P,0) of both solutions prior to mixing. We construct three reduced phase diagrams in the p_(P,0) − r, r − p_(s,0), and p_(s,0) − p_(P,0) planes, respectively, and examine the evolution of the volume fraction of the coexisting phases, concentration of the PE and small-ion species in each phase, and the Galvani potential Ψ_G, as functions of these experimental controlling parameters. We rationalize our findings in terms of the key thermodynamic factors, namely, the translational entropy of the small ions, the electrostatic correlation energy, and the requirement for charge neutrality.

Additional Information

© 2018 AIP Publishing LLC. (Received 11 March 2018; accepted 23 April 2018; published online 6 July 2018) SPECIAL TOPIC: CHEMICAL PHYSICS OF CHARGED MACROMOLECULES This work was conducted jointly by King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia and California Institute of Technology (Caltech) under a collaborative research program in catalysis. The authors gratefully acknowledge the support provided by KFUPM and Caltech. J.W. acknowledges partial financial support from the U.S. National Science Foundation (Grant No. NSF-CBET-8200852353).

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Published - 1.5028524.pdf

Supplemental Material - .listing

Supplemental Material - SI_ComplexCoacervation.pdf


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