Unified explanation for self-assembly of polymer-brush-modified nanoparticles in ionic liquids

We determined the higher-order structures of polymer-brush-modified nanoparticles (PSiPs) in ionic liquids and explained the self-assembled structures as functions of the PSiP concentrations and brush lengths. The two types of brushes applied herein exhibited comparable structure formation patterns, suggesting that self-assembly of the PSiPs was entropy-driven. The crystallization threshold concentration of the PSiPs was understood through the Kirkwood–Alder transition in the assembly by considering the effective particle sizes. The crystal structure of the PSiP was characterized as a random hexagonal close-packed structure in the concentrated-polymer-brush regime, which exhibited the characteristics of hard spheres. In contrast, face-centered cubic (fcc) and body-centered cubic structures were observed in the semidilute-polymer-brush regime, reflecting softening of the interparticle potential. In addition, formation of the fcc structure was possibly due to partial compression and an imbalance in the swollen brush layer caused by the increased brush length and particle concentration. The higher-order structures of polymer-brush-modified nanoparticles (PSiPs) in ionic liquids were analyzed using ultrasmall-angle X-ray scattering. The self-assembly of the PSiPs was entropy-driven. The transition threshold concentration of the PSiPs was understood through the Kirkwood–Alder transition by considering the effective particle sizes. The random hexagonal close-packed structure in the concentrated-polymer-brush regime exhibited the characteristics of hard spheres, whereas face-centered cubic and body-centered cubic structures in the semidilute-polymer-brush regime reflected softening of the interparticle potential.