Abstract
A study of the impact of the size and shape of a nanoparticle on the evolution of structure and surface
segregation in polymer nanocomposite thin films is presented. This is realized by monitoring the
evolution of structure with thermal annealing and equilibrium depth profile of a deuterated polystyrene/
protonated polystyrene bilayer in the presence and absence of various nanoparticles. For the three
shapes examined, sheet-like graphene, cylindrical carbon nanotubes, and spherical soft nanoparticles,
the presence of the nanoparticles slowed the inter-diffusion of the polymers in the thin film. The larger
nanoparticles slowed the polymer motion the most, while the smaller spherical nanoparticles also
significantly inhibited polymer chain diffusion. At equilibrium, the soft spherical nanoparticles, which are
highly branched, segregate to the air surface, resulting in a decrease in the excess deuterated PS at the
surface. The graphene sheets and single walled carbon nanotubes, on the other hand, enhanced the dPS
segregation to the air surface. The graphene sheets were found to segregate to the silicon surface, due to their higher surface energy. Interpretation of these results indicates that entropic factors drive the
structural development in the nanocomposite thin films containing the spherical nanoparticles, while
a balance of the surface energies of the various components (i.e. enthalpy) controls the thin film
structure formation in the polymer-carbon nanoparticle nanocomposites.
