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Effect of charge regulation and conformational equilibria in the stretching properties of weak polyelectrolytes

P. M. Blanco, S. Madurga, F. Mas, J. L. Garcés.
Macromolecules 52 (2019) 8017-8031.

Scheem of a weak polyelectrolyte model under the influence of pH, ionic strength and external force. Monomers are represented as sites joined by flexible harmonic bonds.

Weak polyelectrolytes can modulate their charge in response to external perturbations, such as changes in the pH, ionic strength (I), or electrostatic interactions with other charged species, a phenomenon known as charge regulation (CR). On the other hand, it is well established that CR is highly coupled with the conformational degrees of freedom. In this paper, the influence of CR in the stretching properties of weak polyelectrolytes is analyzed, and the possibility of CR induced by mechanical stretching is explored. With this aim, we make use of a minimal model, which captures the fundamental aspects present in the stretching of a flexible weak linear polyelectrolyte: internal angle rotation, bond stretching, bond bending, and proton binding, which is the paradigmatic mechanism of CR. Mechanical stretching is studied by performing semi-grand canonical Monte Carlo simulations at different pH and ionic strength conditions.