Hofmeister Effect-Mediated Liquid-Air Interfacial Assembly of PEG-Coated Gold Nanoparticles for Large-Area Monolayer Films.

Polymer-grafted nanoparticles (PGNPs) provide a model platform for investigating the interplay between polymer solvation and interfacial assembly. However, the behavior of PGNPs bearing hydrophilic chains at liquid-air interfaces remains poorly understood due to their strong affinity for aqueous subphases. In this work, we examine the interfacial assembly of polyethylene glycol (PEG)-grafted gold nanoparticles (AuNP@PEG) under conditions where polymer solubility is modulated by Hofmeister ions. By systematically varying the identity and concentration of kosmotropic anions, we demonstrate that ion-specific regulation of PEG hydration significantly alters nanoparticle-subphase interactions, leading to a transition from dissolution-dominated behavior to stable interfacial retention and monolayer formation. The dependence of this transition on PEG molecular weight reveals the critical role of chain length in governing desolvation and interfacial free energy. In addition, PEG/polystyrene (PS) co-functionalized nanoparticles are employed to further tune interfacial affinity, providing a comparative framework for disentangling the contributions of polymer solubility and ligand hydrophobicity. These results establish a mechanistic picture in which ion-mediated changes in polymer hydration control nanoparticle residence and assembly at interfaces. This study provides insight into the coupling between polymer solvation and interfacial behavior in PGNP systems and offers a basis for extending interfacial assembly to hydrophilic polymer-grafted nanomaterials.