Ultrasmall Nanoparticles Diluted Chain Entanglement in Polymer Nanocomposites

Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasmall regime defined by de Gennes. However, the mechanism is still ambiguous due to the lack of suitable model systems. Here, we develop an ultrasmall nanoparticle system by using a bimodal grafting strategy to graft both short alkyl chains and long polystyrene chains onto the polyoxometalate molecular nanoparticles with a tunable repulsive potential between the nanoparticles, thus facilitating their uniform dispersion in polystyrene matrices. Linear viscoelasticity of the resultant nanocomposites changes with increasing the filler content, which shows a decrease in both plateau modulus and terminal relaxation time, indicative of a dilution effect of the nanoparticles. Namely, the entanglement network becomes sparser with increasing the filler content.