Nonisotropic Self-Organization of Single-Component Hairy Nanoparticle Assemblies

Solvent-free assemblies of hairy nanoparticles (HNPs) are providing avenues to avoid issues of mixing, agglomeration, and limited inorganic content that plague nanocompositses based on polymer-nanoparticle blending. Here we demonstrate that the order within, and the elongational characteristics of, the neat HNP assembly (aHNP) evolve as the architecture of the polymeric corona in solution transitions from the concentrated (CPB) to semidilute (SDPB) polymer brush regimes (silica nanoparticle: radius r₀ = 8 nm with 120 kDa polystyrene grafts at σ = 0.01-0.1 chains/nm²). Specifically, local HNP packing adopts a nonisotropic local arrangement at intermediate graft densities where the transition from CPB-to-SDPB in solution is approximately r₀. In concert, the neat HNP assembly responds to viscoelastic elongational deformation in a manner analogous to semicrystalline elastomers. Domain orientation under load and subsequent buckling upon recovery lead to the appearance of two- and four-point small-angle X-ray patterns. The correlation between the corona architecture of the HNP and the physical characteristics of the solvent-free aHNP provides a framework akin to block-copolymers to tune mechanical, optical, and electrical properties of fibers and films via ordered mesoscale morphology.