  Introducing nanorods into a polymeric matrix can enhance the physical and
mechanical properties of the resulting material. In this paper, we focus on
understanding the dispersion and orientation patterns of nanorods in an
unentangled polymer melt, particularly as a function of nanorod concentration,
using Molecular Dynamics (MD) simulations. The system is comprised of flexible
polymer chains and multi-thread nanorods that are equilibrated in the NPT
ensemble. All interactions are purely repulsive except for those between
polymers and rods. Results with attractive versus repulsive polymer-rod
interactions are compared and contrasted. The concentration of rods has a
direct impact on the phase behaviour of the system. At lower concentrations
rods phase separate into nematic clusters, while at higher concentrations more
isotropic and less structured rod configurations are observed. A detailed
examination of the conformation of the polymer chains near the rod surface
shows extension of the chains along the director of the rods (especially within
clusters). The dispersion and orientation of the nanorods is a result of the
competition between depletion entropic forces responsible for the formation of
rod clusters, the enthalpic effects that improve mixing of rods and polymer,
and entropic losses of polymers interpenetrating rod clusters.
