Modeling the Morphology and Phase Behavior of One-Component Polymer-Grafted Nanoparticle Systems

Polymer-grafted, or “hairy” nanoparticles (HNP) represent an important and relatively new class of materials. One-component (no matrix) HNP materials, in particular, are not prone to macroscopic phase separation and have a variety of interesting microphase-separated, anisotropic morphologies, similar to surfactants or block copolymers. Here, we develop a new self-consistent field theory describing the behavior of one-component HNP systems, and apply it to predict the morphology as function of the ligand molecular weight and grafting density. As in the case of block copolymers, we observe lamellar, cylindrical, and spherical morphologies, and elucidate phase boundaries as function of the core (nanoparticle) volume fraction and the ratio of the particle radius to the ligand radius of gyration. We also observe the formation of a novel phase, labeled as “sheets”, where the lamellar-like ordering of particle-rich and ligand-rich layers is characterized by the hexagonal ordering of the particles within the particle-rich layer. The predictions agree qualitatively with experimental results. Our theoretical approach can be easily extended to HNPs with mixed ligands and block-copolymer ligands.