| Polymer nanocomposite is a kind of new materials developed in recent years. Synthesizing the qualified nanocomposites and investigating their physical properties and rheological behavior are promising. Rheological information may also help to reveal microscopic structure and macroscopic physical properties. Both aspects are addressed in this work of polymer/layered silicate nanocomposites, crosslinked polystyrene nanospheres and their mixture with linear monodisperse polystyrene.; A rheological approach was used to investigate the properties of a nanoclay-based dispersion firstly. As the preliminary work, it depicts how incorporation of silicate particles produces networking upon ultra-sound induced exfoliation, which offers useful insight into the reinforcement mechanism in the following polymer/layered silicate system. Based on the suspension consisting of xylene and organo-modified layered silicate, it was found that the reinforcement and yield behavior are due to the formation of a percolated filler-filler network structure. Consistent with the yield behavior, the dispersion displays a steady shear viscosity in the controlled rate mode that scales reciprocally with the applied shear rate. The Payne effect, which is a nonlinear viscoelastic phenomenon referring to reduced modulus at large shear amplitude, results from the disruption of filler-filler structure.; In order to achieve exfoliated polymer/layered silicate nanocomposite, we have carried out in-situ free radical bulk polymerization of styrene and methyl methacrylate (MMA) monomers in presence of surfactant modified montmorillonite (MMT) clay. The native MMT clay was modified by a mixture of two commercial cationic surfactants. Exfoliated polystyrene or PMMA/layered silicate nanocomposites were obtained. The exfoliated structure was verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanocomposites show much higher decomposition temperature, higher dynamic modulus, stronger shear thinning behavior and a smaller die swell ratio comparing with pure polymer matrix. From the rheological results, the solid like behavior in linear viscoelastic measurements as well as the yield behavior implies formation of a percolating structure made of the exfoliated clay particles. Other systems were also studied for comparison, including samples made by solution blending with the modified MMT and by in-situ polymerization with commercial clay. These samples show similar rheological properties, but are less stable mechanically.; The zero dimensional nanofillers, i.e., crosslinked PS nanospheres, were synthesized by emulsion and microemulsion polymerization. The diameter of crosslinked nanospheres is rather monodisperse on the order of 10nm. The rheological properties of nanospheres and their blends with linear monodisperse PS were explored. In contrast to the literature report, the nano-PS spheres were found to act like conventional fillers, i.e., to increase the linear viscoelastic properties when incorporated into linear PS melts. Conversely, the pure nano-PS spheres as a nano granular material are found to be "lubricated" by mixing with linear PS melts. |
