Conformation and Ionization Behavior of Charge-Regulating Polyelectrolyte Brushes in a Poor Solvent

Understanding the structural response
of weak polyelectrolyte brushes
upon external stimuli is crucial for their applications ranging from
modifying surface properties to the development of smart and intelligent
materials. In this work, coarse-grained molecular dynamics simulations
were carried out to investigate the conformation and ionization behavior
of charge-regulating polyelectrolyte brushes under poor solvent conditions,
using an implicit solvent model. The results show that, while the
thickness of a sparse polyelectrolyte brush shows a similar behavior
to that of a single chain, namely, a monotonic change as a function
of solvent quality (modeled by an effective segment–segment
attraction strength parameter) and solution pH, a dense polyelectrolyte
brush exhibits more complex behavior. An unexpected reexpansion is
observed when the effective segment–segment attraction strength
is further increased, especially in the case of a high pH. In the
latter case, strong attraction in polymer segments promotes the formation
of large, interchain, cylindrical aggregates, leading to an increase
in brush thickness.