Assembly of diblock copolymer functionalized spherical nanoparticles as a function of copolymer composition
CE Estridge and A Jayaraman, JOURNAL OF CHEMICAL PHYSICS, 140, 144905 (2014).
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 size and tendency to form anisotropic clusters is increased. (C) 2014 AIP Publishing LLC.
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