We cordially invite you to attend the public defense of David Beyer's doctoral thesis titled "Charge Regulation in Soft Matter" on 15th December at 12.30 in the ICP lecture room. The defense will be followed by a reception where you can congratulate the candidate and engage in discussion about the research.
Abstract:
Electrostatic interactions are of paramount importance in the realms of soft and biological matter, shaping the behaviors of polyelectrolytes, proteins and charged colloids. A particularly intriguing effect in charged soft matter is "charge regulation", the phenomenon in which chemically reactive acid or base groups dynamically adjust their charge state in response to the pH value and the local electrostatic environment. However, despite the significance of charge regulation for a plethora of prospective applications, most theoretical treatments to date neglect this effect completely. We use coarse-grained simulations to contribute to the study of charge regulation phenomena in soft matter. First, we investigate the impact of charge regulation on weak polyelectrolyte complexation. Using free energy calculations, we demonstrate that charge regulation significantly alters the binding affinity of the formed polyelectrolyte complex. Inspired by recent experiments, we study the influence of salt on the ionization response of weak polyelectrolyte brushes. Our comparison of particle-based simulations with mean-field calculations demonstrates that for densely grafted brushes, the experimentally observed pKA shifts can be explained using a simple mean-field picture. Subsequently, we extend our brush model to study the influence of divalent counterions on weak polyelectrolyte brushes. In the presence of divalent ions, we predict a new kind of two-stage swelling. Overall, our results demonstrate that charge regulation often leads to complex and surprising behaviors that are absent in systems with fixed charges.