Effects of shape and flexibility of conductive fillers in nanocomposites on percolating network formation and electrical conductivity

Nanocomposites consist of nanofillers and matrices, thus allowing one to design novel materials with desirable properties of both nanofillers and matrices. The percolating network formation of nanofillers in matrices is critical to such desired properties. Some nanofillers such as carbon nanotubes and graphene nanosheets are so flexible that they become either wavy or crumpled. Such a variability in the nanofiller conformation may affect the percolating network formation but has been often (but not always) ignored in the theoretical and computational investigation. In this work, we investigate how the flexibility of different kinds of nanofillers influences the formation of the percolating network by performing extensive Langevin dynamics simulations. We consider three kinds of nanofillers of different shape: nanospheres, nanorods, and nanoplates. When the sizes of nanofillers (or the radius of gyration, Rg) are comparable, nanorods form a percolating network at a lower volume fraction than nanoplates while nanofillers require the highest volume fraction to form the percolating network, which is consistent with previous experiments. The percolation threshold concentration (φc) of nanospheres increases with an increase in their Rg, while φc of nanorods and nanoplates decrease with Rg. However, the effect of flexibility on the percolation threshold volume fraction is much more significant for nanoplates than nanorods. We also estimate the electric conductivity and find that the electric conductivity follows a scaling relation faithfully but with different critical exponents depending on the shape and flexibility.