The pH-Dependent Swelling of Weak Polyelectrolyte Hydrogels Modeled at Different Levels of Resolution

The swelling of polyelectrolyte hydrogels has been often explained using simple models derived from the Flory–Rehner model. While these qualitatively predict experimentally observed trends, they also introduce strong approximations and neglect some important contributions. Consequently, sometimes incorrectly ascribe trends to contributions which are minor importance under given conditions. In this work, we investigate properties weak (pH-responsive) gels at various pH salt concentrations, a hierarchy models, gradually introducing approximations. For first time, three-dimensional particle-based model accounts for topology hydrogel network, electrostatic interactions between gel segments small ions, acid–base equilibrium coupled Donnan partitioning ions. This is most accurate one; therefore, use it as reference when assessing effect As approximation, affine deformation, allows us replace network many chains by single chain, while retaining representation. next step, mean-field approximation particles density fields, combining Poisson–Boltzmann equation with elastic stretching chain. Finally, an ideal neglecting electrostatics all other features previous Comparing predictions four understand dominate high or low concentrations. We observe that field-based overestimate ionization degree because underestimate interactions. Nevertheless, cancellation effects on causes both consistently function concentration. Thus, can conclude any employed rationalize known experimental in swelling, however, only fully account true causing trends. full understanding differences interpreting results framework existing theories ascribing particular contributions, such osmotic pressure,