On the Difference in Ionization Properties between Planar Interfaces and Linear Polyelectrolytes

Ionizable planar interfaces and linear polyelectrolytes show markedly different proton-binding behavior. Planar interfaces protonate in a single broad step, whereas polyelectrolytes mostly undergo a two-step protonation. Such contrasting behavior is explained using a discrete-charge Ising model. Thi...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1997-04, Vol.94 (8), p.3499-3503
Main Authors: Borkovec, Michal, Daicic, John, Ger J. M. Koper
Format: Article
Language:English
Subjects:
Approximation
Capacitance
Cylinders
Dielectric materials
Electrolytes
Electrolytes - chemistry
Electrostatics
Fatty Acids - chemistry
Geometry
Ionization
Ions
Ising model
Models, Chemical
Physical Sciences
Proteins
Titration
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Summary:Ionizable planar interfaces and linear polyelectrolytes show markedly different proton-binding behavior. Planar interfaces protonate in a single broad step, whereas polyelectrolytes mostly undergo a two-step protonation. Such contrasting behavior is explained using a discrete-charge Ising model. This model is based on an approximation of the ionizable groups by point charges that are treated within a linearized Poisson-Boltzmann approximation. The underlying reason as to why planar interfaces exhibit mean-field-like behavior, whereas linear polyelectrolytes usually do not, is related to the range of the site-site interaction potential. For a planar interface, this interaction potential is much more long ranged if compared with that of the cylindrical geometry as appropriate to a linear polyelectrolyte. The model results are in semi-quantitative agreement with experimental data for fatty-acid monolayers, water-oxide interfaces, and various linear polyelectrolytes.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.94.8.3499