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Published December 14, 2021 | Supplemental Material
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Interfacial Structure and Tension of Polyelectrolyte Complex Coacervates


We develop a simple inhomogeneous mean-field theory to study the interfacial structure and tension of polyelectrolyte complex coacervates in equilibrium with a supernatant solution. Our theory treats the electrostatic correlation by combining the Debye–Hückel theory with the first-order thermodynamic perturbation theory within the local density approximation, and incorporates the conformation entropy contribution for both polyions using Lifshitz's ground-state dominance approximation. Using this theory, we systematically examine the interfacial properties of both symmetric and concentration-asymmetric coacervates. The interfacial tension γ is generally rather low, on the order of 1 mN/m or less. For asymmetric coacervates, an intricate electric double layer forms in the interfacial region, which can even contain several oscillations under certain conditions. The interfacial tension generally decreases with increasing the stoichiometric asymmetry, the added-salt concentration, and the initial polymer concentration of the mixture. We further find that the interfacial tension can be quantitatively related to the degree of phase separation S, where S is the Euclidean distance in composition between the two coexisting phases. In particular, we find that γ as a function of S for different concentration asymmetries collapses approximately to two master curves, which merge together and follow γ ∼ S³ for small S.

Additional Information

© 2021 American Chemical Society. Received 28 August 2021. Revised 21 October 2021. Published online 15 November 2021. P.Z. acknowledges the financial support provided by the National Natural Science Foundation of China (21803011 and 22073016) and the award of Shanghai Dongfang Scholar. Z.-G.W. acknowledges the financial support from the Hong Kong Quantum AI Lab Ltd. The authors declare no competing financial interest.

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