Monte Carlo simulation of the stability and structure of polyethylene oxide nanodroplet with different solvent qualities

Abstract

Monte Carlo simulation for poly(ethylene oxide), PEO, was applied to study the effect of solvent quality on the stability and structure of PEO nanodroplets in the poor solvent regime. The Hamiltonian included intrachain and non-bonded interactions. The intrachain interactions were based on an extended rotational isomeric state (RIS) model, and the non-bonded interactions were based on a discretized form of the Lennard-Jones (LJ) potential. The solvent was included implicitly into the simulations by manipulating the attractive portion of the long-range interactions. The results of the simulations clearly showed that as the solvent became poorer, the nanodroplet became denser, and their interfacial thickness decreased. These changes led to PEO chains assuming more compact conformations to enable better packing in the bulk region of the nanodroplets. The average shape of the nanodroplets changed from spherical to ellipsoidal as the solvent quality decreased. This shape anisotropy was attributed to chains assuming compact conformations while trying to pack more efficiently in the bulk region. The chain end bead distribution was strongly influenced by the solvent quality. As the solvent became poorer, a greater proportion of the end beads were excluded from the bulk region because of the need to achieve better packing. Simulations also suggested the formation of a layered structure as the solvent quality decreased.