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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 15:59:22 +0000Electrostatic correlations and the polyelectrolyte self energy
https://resolver.caltech.edu/CaltechAUTHORS:20170224-103032443
Authors: {'items': [{'id': 'Shen-Kevin', 'name': {'family': 'Shen', 'given': 'Kevin'}, 'orcid': '0000-0001-9715-7474'}, {'id': 'Wang-Zhen-Gang', 'name': {'family': 'Wang', 'given': 'Zhen-Gang'}, 'orcid': '0000-0002-3361-6114'}]}
Year: 2017
DOI: 10.1063/1.4975777
We address the effects of chain connectivity on electrostatic fluctuations in polyelectrolyte solutions using a field-theoretic, renormalizedGaussian fluctuation (RGF) theory. As in simple electrolyte solutions [Z.-G. Wang, Phys. Rev. E 81, 021501 (2010)], the RGF provides a unified theory for electrostatic fluctuations, accounting for both dielectric and charge correlation effects in terms of the self-energy. Unlike simple ions, the polyelectrolyte self energy depends intimately on the chain conformation, and our theory naturally provides a self-consistent determination of the response of intramolecular chain structure to polyelectrolyte and salt concentrations. The effects of the chain-conformation on the self-energy and thermodynamics are especially pronounced for flexible polyelectrolytes at low polymer and salt concentrations, where application of the wrong chain structure can lead to a drastic misestimation of the electrostatic correlations. By capturing the expected scaling behavior of chain size from dilute to semi-dilute regimes, our theory provides improved estimates of the self energy at low polymer concentrations and correctly predicts the eventual N-independence of the critical temperature and concentration of salt-free solutions of flexible polyelectrolytes. We show that the self energy can be interpreted in terms of an infinite-dilution energy μ^(el)_(m,0) and a finite concentration correlation correction μ^(corr) which tends to cancel out the former with increasing concentration.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9q7zx-tey21Polyelectrolyte Chain Structure and Solution Phase Behavior
https://resolver.caltech.edu/CaltechAUTHORS:20180221-073146606
Authors: {'items': [{'id': 'Shen-Kevin', 'name': {'family': 'Shen', 'given': 'Kevin'}, 'orcid': '0000-0001-9715-7474'}, {'id': 'Wang-Zhen-Gang', 'name': {'family': 'Wang', 'given': 'Zhen-Gang'}, 'orcid': '0000-0002-3361-6114'}]}
Year: 2018
DOI: 10.1021/acs.macromol.7b02685
Using a recently developed renormalized Gaussian fluctuation (RGF) field theory that self-consistently accounts for the concentration-dependent coupling between chain structure and electrostatic correlations, we study the phase behavior of polyelectrolyte solutions, with a focus on the effects of added salts and chain structure. For solutions of a single polyelectrolyte species plus salt, the RGF theory predicts the existence of a loop in the phase boundary at Bjerrum lengths (inverse temperature) below (above) the critical value of the salt-free system. This loop behavior can occur at electrostatic interaction strengths lb/b at which the loop no longer exists for the TPT-1 theory, and at fixed lb/b the loop can persist for infinitely long chains, in contrast to theories using a fixed-Gaussian structure (fg-RPA). For systems of oppositely charged (but otherwise symmetric) chains, we again find that the fg-RPA greatly overpredicts the driving force for phase separation, especially at higher charge fractions (but still below the critical Manning charge density). In general, stiff chains have a narrower two-phase region than intrinsically flexible chains, although intrinsically flexible chains can still experience a local stiffening which persists in semidilute solution; for higher charge fractions the local stiffening of flexible chains is crucial for reproducing qualitatively correct thermodynamics and phase diagrams. For fully charged flexible chains, we find that phase diagrams are quite similar to those for semiflexible rods and that it is possible to capture the coacervate phase diagrams of the full self-consistent calculations using a constant, renormalized chain stiffness.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/27x1y-1ha05Salt Partitioning in Complex Coacervation of Symmetric Polyelectrolytes
https://resolver.caltech.edu/CaltechAUTHORS:20180718-144046071
Authors: {'items': [{'id': 'Zhang-Pengfei', 'name': {'family': 'Zhang', 'given': 'Pengfei'}, 'orcid': '0000-0002-4226-1394'}, {'id': 'Shen-Kevin', 'name': {'family': 'Shen', 'given': 'Kevin'}, 'orcid': '0000-0001-9715-7474'}, {'id': 'Alsaifi-N-M', 'name': {'family': 'Alsaifi', 'given': 'Nayef M.'}, 'orcid': '0000-0003-3232-6411'}, {'id': 'Wang-Zhen-Gang', 'name': {'family': 'Wang', 'given': 'Zhen-Gang'}, 'orcid': '0000-0002-3361-6114'}]}
Year: 2018
DOI: 10.1021/acs.macromol.8b00726
We perform a general thermodynamic analysis for the
salt partitioning behavior in the coexisting phases for symmetric
mixtures of polycation and polyanion solutions. We find that salt
partitioning is determined by the competition between two factors
involving the ratio of the polyelectrolyte concentration in the coacervate phase to that in the supernatant phase and the difference in the exchange excess chemical potential Δμ_(ex) -- the excess chemical potential difference between PE segments and small ions --
between the coexisting phases. The enrichment of salt ions in the coacervate phase predicted by the Voorn−Overbeek theory is shown to arise from its neglect of chain connectivity in the excess free energy which results in Δμ_(ex) = 0 under all conditions. We argue that chain connectivity in general leads to a finite value of Δμex, which decreases with increasing PE concentration. Explicit calculations using theories that include the chain connectivity correlations -- a simple liquid-state theory and a renormalized Gaussian fluctuation theory -- show nonmonotonic behavior of the salt-partitioning coefficient (the ratio of salt ion concentration in the coacervate phase to that in the supernatant phase): it is larger than 1 at very low salt concentrations, reaches a minimum at some intermediate salt concentration, and approaches 1 at the critical point. This behavior is consistent with recent computer simulation and experimental results.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s6egs-mce48