Abstract
The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and are often
difficult to determine experimentally. To address this shortcoming, we have developed a novel method
to determine the tracer diffusion coefficient of soft polystyrene nanoparticles in a linear polystyrene
matrix. Monitoring the interdiffusion of soft nanoparticles into a linear polystyrene matrix provides the
mutual diffusion coefficient of this system, from which the tracer diffusion coefficient of the soft
nanoparticle can be determined using the slow mode theory. Utilizing this protocol, the role of
nanoparticle molecular weight and rigidity on its tracer diffusion coefficient is provided. These results
demonstrate that the diffusive behavior of these soft nanoparticles differ from that of star polymers,
which is surprising since our recent studies suggest that the nanoparticle interacts with a linear polymer
similarly to that of a star polymer. It appears that these deformable nanoparticles mostly closely mimic
the diffusive behavior of fractal macromolecular architectures or microgels, where the transport of the
nanoparticle relies on the cooperative motion of neighboring linear chains. The less cross-linked, and
thus more deformable, nanoparticles diffuse faster than the more highly crosslinked nanoparticles,
presumably because the increased deformability allows the nanoparticle to distort and fit into available
space.
