Computer simulation of polymer-organoclay nanocomposites for packaging applications: from binding energy to interlayer spacing predictions

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. Common clays are naturally occurring minerals, and are thus subject to natural variability in their constitution. Many clays are aluminosilicates, the most common of which is montmorillonite (MMT). Depending on the precise chemical composition of the clay, the sheets bear a charge on the surface and edges, this charge being balanced by counter-ions, which reside in part in the inter-layer spacing of the clay. One important consequence of the charged nature of the clays is that they are generally highly hydrophilic species, and hence naturally incompatible with a wide range of polymer types. A necessary prerequisite for successful formation of polymer-clay nanocomposites is therefore alteration of the clay polarity to make the clay “organophilic”. Organophilic clay can be produced from normally hydrophilic clay by ion exchange with an organic cation such as an alkylammonium ion (quat). The way in which this is done has a major effect on the formation of particular nanocomposite product.