Modeling Weak Polyelectrolyte Behavior and Predicting Complexation Properties

Weak polyelectrolytes are macromolecules that have titratable groups which may either protonate or deprotonate depending upon the environmental conditions such as pH and salt concentration, which contrasts with strong polyelectrolytes that completely ionize in solution. These molecules find application in abroad class of stimuli responsive materials such as self-assembled copolymer membranes, polymer-coated nanoparticles, polyelectrolyte microgels, drug delivery, gene therapy and hydrogel networks. As there is a complex design space possible for these and other applications of weak polyelectrolytes in terms of structure and responsiveness, it is imperative that one be able to understand quantitatively the dissociation properties of these systems under variable acidity and salinity. Quantitative modeling in computer simulations is particularly useful, as it offers methods to predictively engineer systems for desired response characteristics, enabling time-consuming syntheses to focus on the best candidate systems. This dissertation focuses on utilizing Monte Carlo and Molecular dynamics routines to model the behavior of weak polyelectrolytes in different solution conditions and then exploring their unique complexation properties as well as their applications. We begin by introducing weak polyelectrolytes and then series of studies investigating their properties are presented. First, we investigate the effects of varying topology, pH, salt concentration, counterion valence on the ionization and Coil-Globule Transition (CGT) of these polymers. Then we extend these routines by incorporating advanced sampling method to elucidate on the thermodynamics behind weak polyelectrolyte complexation. Finally, via molecular simulations, we model the ion rejection process in self-assembled copolymer membranes and discuss the thermodynamics of stimuli responsive nanofiltration membranes with pore confined weak polyelectrolyte brushes and outlook with regards to weak polyelectrolyte simulations and applications.