Regensburg 2022 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 34: Hydrogels and Microgels
CPP 34.1: Talk
Thursday, September 8, 2022, 09:30–09:45, H39
Simulations explain the Swelling Behavior of Hydrogels with Alternating Neutral and Weakly Acidic Blocks — •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, Prague, Czechia
We use computer simulations to study a coarse-grained model of a weak (pH-responsive) polyelectrolyte hydrogel which consists of a covalent, regular tetra-functional network of four-armed neutral and acidic stars, coupled to a reservoir of small ions. A similar system consisting of tetrapoly-(acrylic acid) and tetrapoly(ethylene glycol) was recently investigated experimentally by the Sakai group. 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 salt concentrations and pH values of the reservoir. The results for the swelling ratio are in good agreement with the experimental data for high and intermediate pH values. We obtain titration curves which display a significant deviation from the ideal Henderson-Hasselbalch equation due to charge correlations and Donnan partitioning. Contrary to a previous conjecture, our results show that counterion condensation does not explain the observed swelling behavior. Finally, we investigate the gel structure and observe that the swelling is dominated by the stretching of the acidic blocks.