Curvature Induced Radial and Lateral Heterogeneity of Grafted Polymers

Polymer grafted nanoparticles (PGNPs) have gained prominence as building blocks to generate functional single-component composites (SCCs). Understanding the phase behavior of grafted polymers on a single chain level has been proven essential to engineer surface modifications and PGNP-based SCCs. As the nanoparticle size increases beyond few to tens of nanometer, the surface curvature reduces substantially. We hypothesize that the increased local flatness will affect the lateral organization of the grafted polymer to form pseudo-faceted nanoparticles. Here we tested the hypothesis in the regime where the ratio of particle diameter to polymer radius of gyration in the range of ten to hundred, d/R_g = 10–100 and experimentally demonstrated that d/R_g has direct impact on how the resultant assemblies dissipate external stress. Nanoindentation on thin film and bulk PGNP composites demonstrated a non-linear dependence of mechanical properties on composition. Deformation behavior of PGNP film revealed an anisotropic orientation of the grafted polymers, a deviation from previous reported d/R_g ≈ 1 systems. Single particle indentation also indicated different stages of energy dissipation associated with chain conformation and organization. Present studies clearly showed the need to explore PGNP-based SCCs with particle size in the hundreds of nanometers where new and emergent phenomena may arise when local chain arrangements both in the radial and lateral directions are taken into consideration.