Chemical Compatibility and Reaction-Induced Exfoliation in Photopolymerizable Clay Nanocomposites

Exfoliation of clay nanoparticles is a critical step in achieving unique properties associated with clay-polymer nanocomposites. However, a rational means of designing exfoliated nanocomposites, especially in photopolymerizable systems. remain elusive to date. This study investigates the influence of monomer-clay dispersant interactions on organoclay dispersion behavior in photopolymerizable systems. The dispersion behavior of a nonpolar, nonpolymerizable organoclay in a range of monomers with different sizes and polarity was investigated utilizing X-ray scattering and electron microscopy. Results show that increasing chemical similarity between monomer and organoclay dispersant as well as enhanced polar/nonpolar interaction facilitates exfoliation. Organoclays modified with nonpolar dispersants only intercalates in polar polymers. Conversely, exfoliation of the nonpolar organoclay is facilitated in increasingly nonpolar polymers. A set of quaternary ammonium surfactants modified with methacrylate or thiol functionalities were used as dispersants for new organoclays. These polymerizable organoclays exfoliate more readily in a number of monomer systems as compared to nonpolymerizable organoclays. For polymerizable organoclays, the position of the reactive functional group and the type of functionality influence the degree of exfoliation. Methacrylate functionalized organoclays in which the reactive moiety is located away from the Clay Surface exfoliates before photopolymerization. Thiol functionalized organoclays disperse in a mixture of intercalated and exfoliated domains but exfoliate to a larger degree Clue to copolymerization of thiol and acrylate species in the clay galleries. Polymerizable organoclay systems exhibit higher storage modulus, glass transition temperatures, and enhanced photopolymerization behavior when compared to the nonpolymerizable analogues.