Monte Carlo Simulation of the Structures and Dynamics of Amorphous Polyethylene Nanoparticles

Abstract

Monte Carlo simulations of amorphous polyethylene (PE) nanoparticle have been performed on the second nearest neighbor diamond lattice by including short and long-range interactions. A droplet can be either obtained from equilibrated PE bulk or from nanofiber snapshots by modifying periodic boundary conditions. The presence of attractive long-range interactions gives cohesion to the nanoparticle. PE nanoparticles, which contain up to 72 chains of C100 and have the radius ˜5.0 nm, have been produced and equilibrated on the 2nnd lattice. In these droplets, the density profiles are hyperbolic, with end beads being more abundant than middle beads at the surface. There are orientational preferences at the surface on the scale of individual bonds and whole chains. Comparison of nanoparticles with different sizes, which contain different numbers of chains, does not indicate any significant differences in local and global equilibrium properties – for thickness in the range 5.8 to 7.4 nm. Surface energies are calculated directly from the on-lattice energetics. The mobility of the chain in the droplet at the level of individual chords or an entire chain is greater than in the bulk, and the mobility increases as the size of the droplet decreases.