Charge Regulation Effects in Polyelectrolyte Adsorption.

Polyelectrolyte (PE) adsorption plays a pivotal role in tailoring surface properties, finding diverse applications across scientific and industrial domains. In aqueous environments, these polymers gain charge through the dissociation equilibrium of ionizable groups. Consequently, accurately representing their electrostatic interactions necessitates considering many-body couplings between charge and configuration-a phenomenon known as charge regulation (CR)-instead of relying on the constant charge approximation. Here, we show that CR effects can significantly enhance PE adsorption. In the vicinity of a like-charged interface, where short-range PE-surface attraction drives adsorption, both PEs and the surface undergo a reduction in charges during the adsorption process, especially in a semidilute PE solution. This reduction in charges leads to a noticeable decrease in the electrostatic repulsion barrier, facilitating the adsorption process. Conversely, near an oppositely charged surface, CR effects enhance the electrostatic charges of both PEs and surfaces coherently, suppressing the charge reversal of surface charges and ultimately promoting adsorption. These findings underscore the crucial CR effects in PE adsorption and challenge the direct use of electrostatic charges, typically estimated in bulk systems, for an accurate understanding of adsorption phenomena.