Influence of charged intramolecular hydrogen bonds in weak polyelectrolytes: A Monte Carlo study of flexible and extendible polymeric chains in solution and near charged spheres

For weak polyelectrolytes, the interplay between pH, solvent properties, and polymer structure affects the amount of charges, their distribution, and hence their conformations via Coloumb repulsion. Attractive interactions can also develop between charged and neutral sites counteracting the expected Coulomb-induced expansion. To gauge how such competition affects polyelectrolyte structure and ionization, the titration of a single polyelectrolyte chain, isolated or close to a charged sphere, mimicked with a novel many-body potential model is simulated with Monte Carlo. Apart from showing a 10-fold higher ionization than isolated monomers at low pH, interacting species contracted forming short-range clusters of charged and neutral ionizable groups. The presence of a charged sphere synergically boosted both effects due to monomer interactions, forcing the chains to condense onto its surface at much lower pH. Structural properties, however, seem to be controlled only by the ionization degree despite the presence of the topological restraint represented by the spherical surface. Using Monte Carlo titration results, the equilibrium ionization of isolated chains is also estimated; the results evidence that even weak interactions can easily lead to a doubling of the total charge.J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 650-663 Strong charged hydrogen bonds between conjugated ionized and neutral groups (e.g. R- NH3+NH2-R') present in polymers may influence their behavior as weak polyelectrolytes, making them more inclined to dissociate compared with isolated groups. This may be especially evident at low ionization degree, and it can be accompanied by a reduction in the size (e.g. hydrodynamic radius) of the polymer. A similar effect may appear even in presence of a charged surface.