Microgels are three-dimensional crosslinked polymer networks, ranging in size from nanometers to micrometers, that are swollen by a solvent. They exhibit responsiveness to external stimuli such as temperature, pH, ionic strength, and magnetic fields. For biomedical applications, such as drug delivery, polyampholyte microgels are particularly promising due to their ability to safely transport drugs to target sites and release them through charge reversal triggered by pH changes. This thesis uses Metropolis Monte Carlo simulations to investigate the ionization and swelling behavior of polyelectrolyte and polyampholyte microgels and their capacity to take up guest molecules. A parallelized algorithm developed in this work enables the simulation of more complex topologies, such as core-shell structures, and allows for simulations at higher ionic strengths. The microgel models used in this thesis are based on a coarse-grained model, providing results in qualitative agreement with experimental findings. By systematically varying parameters like pK values, microgel concentration, and ionic strength around a reference system, the influence of these parameters on macroscopic properties, such as the degree of ionization and the radius of gyration, is determined. Additionally, the simulations provide insights into properties that are difficult to obtain experimentally, such as the degree of ionization for both acids and bases within the same microgel, and microscopic information, including local ionization within the microgels. Simulations of core-shell polyampholyte microgels show that the width of the U-shaped swelling curve as a function of pH depends on the relative dissociation constants of acidic and basic monomers. The addition of salt narrows this swelling transitions. Furthermore, microgel swelling correlates approximately linearly with the total network charge. Simulations involving polyelectrolyte and polyampholyte microgels with various types of guest molecules demonstrate the capability of these microgels to take up such molecules. In particular, the model for oligopeptide uptake in polyelectrolyte microgels shows promise for future investigations in combination with experimental studies. Finally, the constant pH method in the canonical ensemble is critically evaluated following criticisms about the approach being implicitly grand-canonical. While titration curves obtained with this method and the reaction ensemble method show significant differences for colloidal particles, they differ only at low degrees of ionization for polyelectrolyte microgels. The results demonstrate that the constant pH method provides a reliable and practical approach for the microgels simulated in this thesis.
Christian Strauch (Wed,) studied this question.