The dispersed state of nanoparticles is essential to determine the properties of polymer nanocomposites. For example, in polymer/clay nanocomposites, the formation of exfoliated clay instead of intercalated clay is considered to be desirable to significantly improve the properties of the resulting nanocomposites. To realize fully exfoliated clay sheets in polymer matrices during melt mixing, a lot of research has been focused on designing novel clay modifiers for organically modified clays (OMCs), modifying polymers, developing special processing technologies, etc. In this presentation, we demonstrate that, the exfoliation of OMC platelets in polar polymer matrix results from a combination of shear and molecular diffusion under shear field. The molecular diffusion of polar polymer chains into the OMC interlayer mainly occurs in the initial period of mixing. The slippage of OMC platelets driven by shear takes place during the morphology evolutions of polymer nanocomposites, which results in the final exfoliated dispersion of OMC. If there is no outside shear field in the fabrication of polymer/clay systems, the formation of an exfoliated clay structure in linear polymers (even compatible one) is difficult from a kinetic point of view. The intercalation of polymer chains into the interlayer of OMC is necessary to realize the exfoliation of OMC sheets, but it is not enough to the formation of exfoliated structure. This results from that the intercalated polymer chains act as a bridge to bind the two surfaces via the attractive interactions between the polymer chains and the OMC. However, if the topology of polymer chains changes from linear structure to star-like one, the exfoliation of OMC sheets can be realized in the case without shear field. Here we provide the insight why these kinds of polymer chains can easily make OMC platelets exfoliated from a kinetic point of view.

Formation of exfoliated polymer/clay nanocomposites at melt state: Mechanism and practice

251st National Meeting (2016)

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