Effect of blockiness in grafted monomer sequences on assembly of copolymer grafted nanoparticles: a Monte Carlo simulation study

Abstract

We use Monte Carlo simulations to study AB copolymer-grafted nanoparticles to elucidate the effect of blockiness (length of contiguous blocks of like-monomers) in the grafted monomer sequence on the shape, size, and structure of assembled nanoparticle clusters for a range of monomer–monomer and monomer–particle interactions. The graft sequence dictates the ease or difficulty of the grafted chains to form attractive like-monomer (A–A or B–B) contacts while minimizing repulsive unlike-monomer (A–B) contacts within an assembled cluster or a dispersed state. When A–B repulsion is negligible, with increasing blockiness at constant graft length the cluster size and average coordination number decrease in the presence of A–A or B–B attractions, and are approximately constant in the presence of A–A and B–B attractions. When A–B repulsion is strong, the cluster size and average coordination number increase with increasing blockiness for small and large particles. For small particles, with strong B–B attraction and A–B repulsion, increasing blockiness leads to increasing anisotropy in cluster shape, while strong A–A attraction produces isotropic clusters regardless of the graft sequence. The effect of graft sequence on cluster shape is reduced for large particles as compared to small particles, at constant graft length. Lastly, the extent to which monomer–particle attractive interactions change the above trends is highly dependent on the relative strength of monomer–particle to monomer–monomer interactions, in addition to the ratio of particle size to graft length, and the grafting density.