Influence of hair density and hair length on interparticle interactions of spherical polymer brushes in a homopolymer matrix

The dynamics of hairy spherical nanoparticles in a melt of linear polymer chains has been investigated by mechanical spectroscopy as a function of particle topology and concentration. Using a simple free volume approach for the data analysis of the structural relaxation time vs concentration and the well-known hard-sphere result as a reference, a semiquantitative measure for the interparticle interactions, that is particle deformability/softness, and the effective particle size compared to the size of a nonswollen spherical brush has been determined. For these studies, model particles of hairy nanoparticles differing in either hair length or grafting density have been prepared. In contrast to our previous studies of copolymer micelles, for the new graft particles at very high grafting densities our free volume approach led to nonphysical results: the effective particle size is increasing with increasing concentration. Therefore, it has been concluded that densely grafted hairy particles in a matrix of linear polymer chains cannot be mapped onto a hard-sphere reference system, indicating that the interaction potential is not simply soft repulsive.