Center for Functional Nanomaterials Seminar

Layered silicates are important fillers for improving various properties of polymers, which can be attributed to their sheet like morphology. Layered silicates can be modified with organic surfactants to render them compatible with polymer matrix. Organically modified silicates (organoclays) upon amalgamating with polymer matrix wherein polymer chains can penetrate in between the silicate layers and result in an intercalated structure where the clay stack remains intact but the interlayer spacing increases. When penetration becomes more severe, disintegration of clay stacks can occur, resulting in an exfoliated structure. It has often been observed that exfoliation is not complete down to the level of isolated silicate layers; rather the large clay stacks are broken up into shorter stacks termed 'tactoids' together with a few individual silicate layers, resulting in a kind of mixed intercalated-exfoliated structure. Organoclays particles are mostly intercalated, having a preferred orientation with the clay gallery planes being preferentially parallel to the plane of the pressed film, which affects the barrier properties of polymeric membranes. Additional fillers like carbon black can induce a change in their orientation. We also investigated the flammability properties of a series of polymer nanocomposites containing Transition Metal Ion (TMI) modified organoclays. The improved fire retardation in nanocomposites can be attributed to enhanced carbonaceous char formation during combustion, in the presence of catalytically active TMI. Polymer nanocomposite materials depend not only on the properties of individual components but also on their morphology and interfacial interactions, which are maximized due to the large surface area of the filler particles exposed to the polymer matrix. This results in unique anisotropic properties hence it will be of great importance to achieve exfoliation of the lamellar stacks prior to mixing.