Molecular simulation of molecular and surface properties of random copolymer nanoparticle

Abstract Random copolymer nanoparticles were studied by Monte Carlo simulation of coarse-grained models on the high coordination lattice. Molecular and surface properties of free-standing nanoparticle were characterized at fixed 50% co-monomer content as a function of the interaction strength between co-monomer units. Intramolecular interaction for all copolymer chains were treated by the Rotational Isomeric State (RIS) model of polyethylene (PE). To simulate the copolymer model, the non-bonded interactions for comonomer units were described by different parameter sets of the Lennard-Jones energy. When the co-monomer interaction was stronger, the bulk densities of nanoparticles were increased and the interfacial widths were narrower. Near the surface, end beads of copolymer chains were segregated and the bond orientation was preferably perpendicular to the surface. Molecular shape and molecular size of copolymer chains were slightly changed as a function of co-monomer interaction strength and most of which occurs close to the surface. For chain orientation, the largest principal axis tended to orient parallelly to the surface, and then changed toward randomly isotropic orientation for weaker co-monomer interaction. The intrachain energies were decreased at the surface region implying more trans conformation while the non-bonded energies were increased due to better monomer packing at the surface region. The change of system energetics was more apparent as a function of the co-monomer interaction.