Regensburg 2022 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 13: Charged Soft Matter, Polyelectrolytes and Ionic Liquid
CPP 13.2: Vortrag
Dienstag, 6. September 2022, 10:00–10:15, H38
Electrostatically Cross-Linked Reversible Gels - Effects of pH and Ionic Strength — Roman Staňo1,4, •Peter Košovan1, Andrea Tagliabue2, and Christian Holm3 — 1Faculty of Science, Charles University, Prague, Czechia — 2Universitá degli Studi dell Insubria, Como, Italy — 3Institute for Computational Physics, University of Stuttgart, Germany — 4University of Vienna, Austria
Mixing of oppositely charged macromolecules can lead to the formation of electrostatically cross-linked coacervate gels. In this simulation study, we determine the conditions under which four-armed star copolymers with charged end-blocks are able to form such coacervate gels. The cationic charged blocks consist of quenched charges, whereas the anionic blocks contain pH-responsive weak acid groups. We used the Grand-reaction method to determine the phase stability, equilibrium composition, and structural properties of these systems in equilibrium with a supernatant solution at various pH levels and salt concentrations. Depending on the pH and hence on the charge state of the polyanion blocks, we observed the emergence of three regimes: a solution, a sol of isolated star clusters, and a gel*percolating network of stars. Moreover, we demonstrate that the charge state of the stars in the gel phase can be well described by the ideal Henderson-Hasselbalch (HH) equation, despite the presence of strong interactions violating ideality. We can explain this surprising result by cancellation of two stongly non-ideal effects. This observation explains why various experiments on coacervate gels can be well described by the HH equation, although its assumption of ideality is violated.