Fabrication of Bragg stack films of clay nanosheets and polycations via co-polymerization of intercalated monomers and functional interlayer cations

Abstract

The fabrication of one-dimensional (1D) crystalline, monodomain nanocomposite films (hybrid Bragg stacks) is still limited to a few combinations of polymers and clay. The main reason is the segregation of clay and polymers driven by the entropic loss faced by the polymer confined in a narrow slit between the nanosheets. By exchanging synthetic sodium-fluorohectorite with vinylbenzyltrimethylammonium chloride, we succeeded in delaminating clay via 1D dissolution in N-methylformamide to obtain a liquid crystalline suspension. By combining this with bisphenol A glycerolate diacrylate, 1D crystalline nanocomposites could be obtained via photopolymerization of doctor bladed wet coatings. Infrared spectroscopy confirmed the co-polymerization of monomers and the organic modifier between the hectorite platelets. This single-phase hybrid material shows very low oxygen and water vapor transmission rates. The incorporation of the modified clay into the polymer leads to an oxygen transmission rate of 0.21 cm³ m⁻² day⁻¹ atm⁻¹ at 50% r.h. and 23 °C and a water vapor transmission rate of 0.05 g m⁻² day⁻¹ for a coating of 3.7 μm, making this material appropriate for challenging packaging applications.