(268f) Self-Assembly of Grafted Nanoparticles in Thin Films

We present a computational study of the structural properties of free-standing thin films of solvent-free polymer grafted nanoparticles, investigated via molecular dynamics simulations. A recent study [1] of the bulk demonstrated that polymer grafted nanoparticles in solvent free condition displayed structural behaviour which deviate significantly from that of simple liquids. We focus here on the possibility to obtain stable 2-dimensional pattern formation of spherically grafted nanoparticles when suspended as a free-standing film. Morphological phase diagrams in terms of particle-particle and particle-polymer attractions are systematically studied for nanoparticles with different grafted chain length. We observe formation of defined structures ranging from dispersed particles, finite stripes to percolating networks in 2 dimensions. Although the formation of stripes for this system is generally understood to be linked to the grafted chain deformation upon aggregation of the particle cores, resulting in an effective “dipolar” interparticle potential, we find that this anisotropic self-assembly can be systematically reproduced by coarse-graining the interactions into 2-dimensional isotropic potentials obtained by a simple inverse-Boltzmann procedure. This suggests that the main driving force for the anisotropic self-assembly for these uniformly grafted nanoparticle is due to the presence of a short-range attraction and long-range repulsion.

[1] Chremos, A.; Panagiotopoulos, A. Z., Phys. Rev. Lett. 2011, 107, 105503