Assembly of diblock copolymer functionalized spherical nanoparticles as a function of copolymer composition

In this work, we use coarse-grained molecular dynamics simulations to study spherical nanoparticles functionalized with AB diblock copolymer chains at low grafting density, to obtain a design library linking copolymer composition, monomer-monomer interaction strengths, graft lengths, particle sizes, and monomer solvent-philicity to the two stages of nanoparticle assembly: the initial formation of patches within the copolymer-grafted particles from attractive monomers aggregating, and then the (equilibrium) assembled cluster formation. With regards to patch formation, as the fraction of the solvent-phobic (A or B) block decreases along the graft and the interaction strength decreases, the propensity to form patches on the particles decreases. As the fraction of the solvent-phobic block increases, the time for patch formation decreases, in particular if the inner A block is solvent-phobic. As the ratio of graft length to particle size increases the propensity to form fewer patches increases due to inter-graft monomer aggregation. For all compositions, the assembled clusters formed in B-selective solvents (solvent-phobic A block) have a higher fraction of particles at smaller inter-particle distances than in A-selective solvents (solvent-phobic B block). In an A-selective solvent at low interaction strengths, as the graft length to particle diameter ratio is increased, the tendency to form isotropic clusters at equilibrium is increased, and intermediate anisotropic chain-like assembly is observed. When these anisotropic intermediate states are observed, they accelerate the formation of equilibrium isotropic clusters. With increasing strength of interaction between solvent-phobic B monomers, the intermediate states disappear from the assembly pathway. At low and intermediate interaction strengths, as fraction of A block increases, the clusters' outer shell of solvent-philic A monomers which surrounds the patch of solvent-phobic B monomers becomes dense, hindering addition of more particles to the cluster leading to smaller overall clusters. In a B-selective solvent, predominantly anisotropic clusters form, and show an increase in shape anisotropy with increasing monomer interaction strength. In both cases of monomer solvent-philicity, with an increase in the graft length to particle diameter ratio we see a decrease in anisotropic cluster formation. And, in both cases of monomer solvent philicity, with increasing monomer interaction strength the average cluster