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Polyelectrolyte Titration: Theory and Experiment Itamar Borukhov,*, David Andelman,,| Regis Borrega, Michel Cloitre, Ludwik Leibler, and
 

Summary: Polyelectrolyte Titration: Theory and Experiment
Itamar Borukhov,*, David Andelman,,| Regis Borrega, Michel Cloitre, Ludwik Leibler, and
Henri Orland§,
Unite´ Mixte de Recherche CNRS/ATOFINA (UMR 167), 95 rue Danton, B.P. 108,
92303 LeVallois-Perret Cedex, France, School of Physics and Astronomy, Raymond and BeVerly Sackler
Faculty of Exact Sciences, Tel AViV UniVersity, Tel AViV 69978, Israel, and SerVice de Physique The´orique,
CE-Saclay, 91191 Gif-sur-YVette Cedex, France
ReceiVed: May 23, 2000; In Final Form: July 31, 2000
Titration of methacrylic acid/ethyl acrylate copolymers is studied experimentally and theoretically. At low
salt concentrations, this polyacid exhibits a plateau in the titration curve below the neutralization point. The
plateau has often been attributed to a first-order phase transition associated with polymer conformational
changes. We argue that the specific shape of titration curves of hydrophobic polyelectrolytes is due to
electrostatics and does not necessarily require a conformation change of the polyelectrolyte chains. We calculate
the free energy at the mean-field level and its first-order (one loop) correction using a loop expansion. The
latter is dominated by Debye-Hu¨ckel-like charge-charge correlations as well as by correlations between
dissociation sites along the polymer chain. We show that the one-loop corrections to the free energy lead to
titration curves that agree with experiments. In particular, the model explains the decrease of the pH at the
plateau when the polymer concentration is increased or when salt is added to the solution.
I. Introduction
In recent years the search for environment-friendly materials

  

Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University

 

Collections: Materials Science; Physics