Tailoring polymer properties with layered silicates

Polymer layered silicate nanocomposites have found widespread applications in areas such as plastics, oil and gas production, biomedical, automotive and information storage, but their successful commercialization critically depends on consistent control over issues such as complete dispersion of layered silicate into the host polymer and optimal interaction between the layered silicates and the polymers.;In particular, the melt rheological properties of layered silicate nanocomposites with maleic anhydride functionalized polypropylene are contrasted to those based on ammonium-terminated polypropylene. While the maleic anhydride treated polypropylene based nanocomposites exhibit solid-like linear dynamic behavior, consistent with the formation of a long-lived percolated nanoparticle network, the single-end ammonium functionalized polypropylene based nanocomposites demonstrated liquid-like behavior at comparable montmorillonite concentrations. The differences in the linear viscoelasticity are attributed to the presence of bridging interaction in maleic anhydride functionalized nanocomposites, which facilitates formation of a long-lived silicate network mediated by physisorbed polymer chains. Further, the transient shear stress of the maleic anhydride functionalized nanocomposites in start-up of steady shear is a function of the shear strain alone and the steady shear response is consistent with that of non-Brownian systems. In addition, the weak dependence on the steady shear stress of the steady first normal stress difference suggests that the polymer chain mediated silicate network contributes to such unique flow behavior.;This dissertation also explores the following aspects. To effectively achieve a stable and exfoliated silicate system, polystyrene tethered layered silicates via nitroxide mediated polymerization are dispersed in a monodisperse lamellar polystyrene polyisoprene diblock copolymer and serve as structure-direct agent, creating nearly oriented structures. In addition, small angle scattering techniques are utilized to examine the degree of dispersion of layered silicate in organic solvents, where the scattering data are fitted to various physical meaningful models, thus providing detailed information on the degree of dispersion and silicate dimensions. Finally, spectroscopic properties of the fluorescent dyes are altered upon adsorption to the silicate surface, providing information about the local environment at the interface and possibly the degree of silicate dispersion. The interactions between dyes, silicates and solvents are examined by fluorescence and UV-Vis spectroscopy.;Polypropylene is a commercially important polymer but usually forms intercalated structures with organically modified layered silicate upon mixing, even it is pre-treated with compatibilizing agent such as maleic anhydride. In this work, layered silicate is well dispersed in ammonium modified polypropylene but does not provide sufficient reinforcement to the host polymer due to poor interactions. On the other hand, interactions between maleic anhydride modified polypropylene and layered silicate are fine tuned by using a small amount of maleic anhydride and mechanical strength of the resultant nanocomposites are significantly enhanced.