Self-assembly of polymer-grafted nanoparticles in thin films.

We use large-scale molecular dynamics simulations with a coarse-grained model to investigate the self-assembly of solvent-free grafted nanoparticles into thin free-standing films. Two important findings are highlighted. First, for appropriately chosen values of system parameters the nanoparticles spontaneously assemble into monolayer thick films. Further, the nanoparticles self-assemble into a variety of morphologies ranging from dispersed particles, finite stripes, long strings, to percolating networks. The main driving force for these morphologies is the competition between strong short-range attractions of the particle cores and long-range entropic repulsions of the grafted chains. The grafted nanoparticle systems provide practical means to realize two-length-scale systems that have been previously seen, using a simple two-dimensional model [G. Malescio and G. Pellicane, Nat. Mater., 2003, 2, 97], to generate a variety of morphologies. However, there are only relatively narrow ranges of interaction strengths and chain lengths for which anisotropic self-assembly is possible.