Effect of nanoparticle size on the mechanical properties of polymer nanocomposites

The mechanical properties of a series of polymer nanocomposites (PNCs) of polyvinylacetate (PVAc) and carbon dots (CDs) with average diameters of 2.5 and 8.5 nm (denoted as CD-2.5 and CD-8.5, respectively) or carbon black (N330) were investigated. The results show that when the nanoparticle size larger than the tube diameter of PVAc, e.g. N330 and CD-8.5, the complex viscosity, reptation relaxation time, and elongation at break of the PNCs get larger with decrease of particle size whereas the tensile stress becomes smaller. For CD-2.5 with size comparable to the Kuhn segment length, the well-dispersed CD-2.5 induces the decrease of complex viscosity and reptation relaxation time, and thus results in an intermediate tensile stress and reduced elongation at break. The possible origins of the different reinforce mechanism were explained and it is inferred that whether the existence of a critical size of the nanoparticles for an effective reinforcement is still needed to be explored.