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Coupling of Charge Regulation and Conformational Equilibria in Linear
Weak Polyelectrolytes: Treatment of Long Range Interactions via
Effective Short-Ranged and pH-Dependent Interaction Parameters
Blanco, P.M.; Madurga, S.; Mas, F.; Garcés, J.L. Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long-Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters. Polymers2018, 10, 811.
Blanco, P.M.; Madurga, S.; Mas, F.; Garcés, J.L. Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long-Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters. Polymers 2018, 10, 811.
Blanco, P.M.; Madurga, S.; Mas, F.; Garcés, J.L. Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long-Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters. Polymers2018, 10, 811.
Blanco, P.M.; Madurga, S.; Mas, F.; Garcés, J.L. Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long-Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters. Polymers 2018, 10, 811.
Abstract
The classical Rotational Isomeric State (RIS) model, originally proposed
by Flory, has been used to rationalize a wide range of physicochemical
properties of neutral polymers. However, many weak polyelectrolytes
of interest are able to regulate their charge depending on the conformational
state of the bonds. Recently, it has been shown that the RIS model
can be coupled with the Site Binding (SB) model, for which the ionizable
sites can adopt two states: protonated or deprotonated. The resulting
combined scheme, the SBRIS model, allows to analyse ionization and
conformational equilibria on the same foot. In the present work this
approach is extended to include pH-dependent electrostatic Long Range
(LR) interactions, ubiquitous in weak polyelectrolytes at moderate
and low ionic strengths. With this aim the original LR interactions
are taken into account by defining effective Short Range (SR) and
pH-dependent parameters, such as effective microscopic protonation
constants and rotational bond energies. The new parameters are systematically calculated using variational methods. The machinery of statistical
mechanics for SR interactions, including the powerful and fast transfer
matrix methods, can then be applied. The resulting technique, to which
we will refer as Local Effective Interaction Parameters (LEIP) method,
is illustrated with a minimal model of a flexible linear polyelectrolyte
containing only one type of rotating bonds. LEIP reproduces very well
the pH dependence of the degree of protonation and bond probabilities
obtained by semi-grand canonical Monte Carlo simulations, where LR
interactions are taken explicitly into account. The reduction in the
computational time in several orders of magnitude suggests that the
LEIP technique could be useful in a range of areas involving linear
weak polyelectrolytes, allowing direct fitting of the relevant physical
parameters to the experimental quantities.
Keywords
polyelectrolytes; charge regulation; long-range
interactions; Debye-Hückel interactions; transfer matrix; Ising models; semi-grand canonical ensemble; Monte Carlo simulations; conformational
equilibria; variational methods
Subject
Chemistry and Materials Science, Physical Chemistry
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
