How antagonistic salts cause nematic ordering and behave like diblock copolymers
Jung WDK, Rivas N, Harting J (2019)
Publication Type: Journal article
Publication year: 2019
Journal
Book Volume: 150
Journal Issue: 6
DOI: 10.1063/1.5085660
Abstract
We present simulation results and an explanatory theory on how antagonistic salts affect the spinodal decomposition of binary fluid mixtures. We find that spinodal decomposition is arrested and complex structures form only when electrostatic ion-ion interactions are small. In this case, the fluid and ion concentrations couple and the charge field can be approximated as a polynomial function of the relative fluid concentrations alone. When the solvation energy associated with transferring an ion from one fluid phase to the other is of the order of a few kBT, the coupled fluid and charge fields evolve according to the Ohta-Kawasaki free energy functional. This allows us to accurately predict structure sizes and reduce the parameter space to two dimensionless numbers. The lamellar structures induced by the presence of the antagonistic salt in our simulations exhibit a high degree of nematic ordering and the growth of ordered domains over time follows a power law. This power law carries a time exponent proportional to the salt concentration. We qualitatively reproduce and interpret neutron scattering data from previous experiments of similar systems. The dissolution of structures at high salt concentrations observed in these experiments agrees with our simulations, and we explain it as the result of a vanishing surface tension due to electrostatic contributions. We conclude by presenting 3D results showing the same morphologies as predicted by the Ohta-Kawasaki model as a function of volume fraction and suggesting that our findings from 2D systems remain valid in 3D.
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Germany (DE)How to cite
APA:
Jung, W.D.K., Rivas, N., & Harting, J. (2019). How antagonistic salts cause nematic ordering and behave like diblock copolymers. Journal of Chemical Physics, 150(6). https://dx.doi.org/10.1063/1.5085660
MLA:
Jung, Wieland David Krischan, Nicolas Rivas, and Jens Harting. "How antagonistic salts cause nematic ordering and behave like diblock copolymers." Journal of Chemical Physics 150.6 (2019).
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