Optimum graft density for dispersing particles in polymer melts

We investigate the dispersion of polymer-grafted particles suspended in a polymer matrix by viscoelastic measurements and electron microscopy. We find that, when the graft density is low, the particle dispersion improves with an increase of the graft density, while the particle dispersion becomes worse when the graft density is too high; i.e., there is an optimum graft density for dispersing the particles. We explain the phenomena by showing that the grafted polymers cause attraction for high graft density.