Morphology evolution and anisotropic phase formation of the maleated polyethylene-layered silicate nanocomposites

Morphology evolution and anisotropic phase formation of the maleated polyethylene-layered silicate nanocomposites are investigated by using synchrotron small-angle X-ray scattering (SAYS), transmission electron microscopy (TEM), and polarized optical microscopy (POM). Despite favorable compatibility between polymer and organically modified layered silicates, the final morphology of the nanocomposite evolves via four stages: disordered exfoliation, ordered exfoliation, dual morphologies of intercalation and exfoliation, and intercalation in sequence with the content of silicate. The formation of the ordered exfoliation state is attributed to the steric interaction between anisotropic silicate plates. Particularly, the transition from exfoliation to intercalation provides us with the significant clue that the interaction between layer silicates gets dominant when the distance between them is smaller than a certain value. It is found that the silicate layers need larger layer spacing than 9 nm to avoid the attractive interaction between adjacent silicate layers and to keep the exfoliation state in this nanocomposite system. Additionally, the nanocomposite shows the optical anisotropy above 12 vol % clay due to the ordering of silicate layers. The optical anisotropy becomes stronger with the content of silicate.