Interfacial properties and hopping diffusion of small nanoparticle in polymer/nanoparticle composite with attractive interaction on side group

Abstract

The diffusion dynamics of fullerene (C60) in unentangled linear atactic polystyrene (PS) and polypropylene (PP) melts and the structure and dynamic properties of polymers in interface area are investigated by performing all-atom molecular dynamics simulations. The comparison of the results in two systems emphasises the influence of local interactions exerted by polymer side group on the diffusion dynamics of the nanoparticle. In the normal diffusive regime at long time scales, the displacement distribution function (DDF) follows a Gaussian distribution in PP system, indicating a normal diffusion of C60. However, we observe multiple peaks in the DDF curve for C60 diffusing in PS melt, which indicates a diffusion mechanism of hopping of C60. The attractive interaction between C60 and phenyl ring side groups are found to be responsible for the observed hopping diffusion. In addition, we find that the C60 is dynamically coupled with a subsection of a tetramer on PS chain, which has a similar size with C60. The phenyl ring on PS chain backbone tends to have a parallel configuration in the vicinity of C60 surface, therefore neighbouring phenyl rings can form chelation effect on the C60 surface. Consequently, the rotational dynamics of phenyl ring and the translational diffusion of styrene monomers are found to be slowed down in this interface area. We hope our results can be helpful for understanding of the influence of the local interactions on the nanoparticle diffusion dynamics and interfacial properties in polymer/nanoparticle composites.