The Relationship Between the Solubility Parameter of Polymers and the Clay-Dispersion in Polymer/Clay Nanocomposites and the Role of the Surfactant
Nanocomposites were prepared of polymers having different solubility parameters and pristine or organically modified clays, and the dispersion of clay in the polymer was evaluated using X-ray diffraction and transmission electron microscopy. The solubility parameters of both the polymers and surfactants of interest were calculated according to the group contribution method and correlated with the clay morphology. A close relationship between the solubility parameter of the polymer and the clay morphology was observed. The clay has a very polar group, so the higher is the solubility parameter of the polymer, the larger is the d spacing of the clay that can be achieved. This can explain why in-situ polymerization shows better dispersion than does melt-blending. It appears that the modification of the surfactants is less important than modification of the polymer. However, an enlarged d spacing by the surfactant enables the insertion of the monomer into the gallery space by in-situ polymerization and allows the polymer chain having a high solubility parameter to penetrate the gallery space of the clay during melt-blending.