Self-standing nanoparticle membranes and capsules.

We perform coarse-grained molecular dynamics simulations of self-standing nanoparticle membranes observed in recent experiments (K. E. Mueggenburg et al., Nat. Mater., 2007, 6, 656). In order to make our simulations feasible, we model 2-3 times smaller gold nanoparticles (core radius of r(core) ≈ 0.8 nm) covered with alkanethiol ligands (length of l(ligand) ≈ 0.5-2.6 nm). We study the structure, stability, and mechanical properties of these membranes and show that these characteristics are controlled by the ratio of R(LC) = l(ligand)/r(core). For R(LC) ≈ 0.6, the ligated nanoparticles form well ordered monolayers with hexagonal packing, in agreement with the experiments (R(LC) ≈ 0.44). For R(LC) ≈ 1.6, the nanoparticles form less organized multilayers, which are more stable and flexible. We show that these membranes could potentially form stable capsules for molecular storage and delivery.