(692b) A Combined Experimental/Computational Approach to the Characterization of Polymer-Clay Nanocomposites Based on Peo-Diacrylate Macromolecules

The subject of hybrids based on layered inorganic compounds such as clays has been studied for a considerable time, but the area is enjoying a resurgence of interest and activity as a result of the exceptional properties which can be realized from such nanocomposites. Materials variables which can be controlled and which can have a profound influence on the nature and properties of the final nanocomposite include the type of clay, the eventual choice of clay pre-treatment, the selection of polymer component and the way in which the polymer is incorporated into the nanocomposite. The synthetic route of choice for making a nanocomposite depends on whether the final material is required in the form of an intercalated or exfoliated hybrid. In the case of an intercalate, the organic component is inserted between the layers of the clay such that the inter-layer spacing is expanded, but the layers still bear a well-defined spatial relationship to each other. In an exfoliated structure, the layers of the clay have been completely separated and the individual layers are distributed throughout the organic matrix. A third alternative is dispersion of complete clay particles (tactoids) within the polymer matrix, but this simply represents use of the clay as conventional filler. In recent years, there has been extensive study of the factors which control whether a particular organo-clay hybrid can be synthesized as an intercalated or exfoliated structure. Since clay nanocomposites can produce dramatic improvements in a variety of properties, it is important to understand the factors that affect delamination of the clay. These factors include, besides the exchange capacity of the clay and the polarity of the reaction medium, the chemico-physical properties of interlayer cations. In this work we present the results of a jointed computational/experimental effort aimed at the study and comprehension of the interactions which occur, at a molecular level, in the formation of polymer-clay nanocomposites based on PEO-diacrylate macromolecules.