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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 15: Poster I

CPP 15.4: Poster

Montag, 18. März 2024, 18:00–20:00, Poster C

Simulations of Weak Polyelectrolyte Hydrogels with Divalent Counterions — •David Beyer¹, Peter Košovan², and Christian Holm¹ — ¹Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany — ²Department of Physical and Macromolecular Chemistry, Charles University, 128 00 Prague 2, Czechia

We use computer simulations to study a coarse-grained model of a weak (pH-responsive) polyelectrolyte hydrogel coupled to a reservoir of small ions, including a 2:1 salt. To model the ionization equilibrium of the weak groups and the exchange of small ions with the reservoir, we make use of the recently developed Grand-Reaction Monte-Carlo method (G-RxMC). We determine the free swelling equilibrium for different concentrations of the divalent salt and pH values of the reservoir. Our simulations show that even a small amount of divalent salt can significantly inhibit the swelling of the gels due to the preferential uptake of divalent ions into the gel, effectively suppressing the swelling for salt concentrations above 10mM. Interestingly, we observe that the gels exhibit a second swelling step at very high pH-values, which is in stark contrast to the behaviour in a monovalent salt solution. This behaviour arises due to an interplay of the ion partitioning and electrostatic interactions.

Keywords: Weak Polyelectrolyte; Monte Carlo; Molecular Dynamics; Multivalency; Partitioning