Synthesis of nanocomposites: Organoceramics
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We report here on the synthesis of new materials termed organoceramics in which polymers are molecularly dispersed within inorganic crystalline phases. These nanocomposite materials may not only have unique morphologies and physical properties but may also lead to new processing methods for ceramic-based materials. In organoceramics polymer molecules could opportunistically occupy sites such as grain boundaries or other two-dimensional defects, nanopores, lattice channels, or interlamellar spaces. Our synthetic approach to get macromolecules to those sites is to nucleate and grow inorganic crystals from homogeneous solutions containing the polymer chains as co-solutes. The new materials discussed in this manuscript were synthesized by growing calcium aluminate crystals in the presence of water soluble polymers and were characterized by x-ray diffraction, scanning electron microscopy, elemental analysis, and diffuse reflectance infrared spectroscopy. The macromolecules used in organoceramic synthesis included poly(vinyl alcohol), poly(dimethyldiallyl ammonium chloride), and poly(dibutyl ammonium iodide). We found that the chemistry of polymer repeats can impact on the spatial distribution of the dispersed organic chains and also on the morphology of organoceramic powders. In the case of the poly(vinyl alcohol) organoceramic the polymer is intercalated in "flattened" conformations in Ca2Al(OH)6[X] • nH 2 O, thus increasing the distance between ionic layers from 7.9 A to ~ 1 8 A (X is a monovalent or divalent anion). Such a layered nanocomposite can be formed only by intercalating the poly(vinyl alcohol) during growth of the Ca2Al(OH)6[X] • nH 2 O crystal. The synthetic pathway is therefore able to overcome large entropic barriers and incorporate significant amounts of polymer in the organoceramic product, in some cases up to 38% by weight. The particles of this nanocomposite are spheroidal aggregates of thin plate crystals whereas the use of a polycationic polymer in the synthesis leads to rod-like particles in which organic chains may reside in channels of the inorganic crystal.
I. INTRODUCTION The development of advanced high-strength composites has been a particularly active area of materials research over the past few decades. The use of organic macromolecules as an integral part of these materials is widespread, most often as matrices reinforced by carbon or glass fibers. Our interest in this work has been to study the synthesis of novel composite materials in which macromolecules are introduced in unique ways within the microstructure. Specifically, we seek to synthesize materials in which macromolecules are molecularly dispersed within inorganic crystalline phases. These materials may not only have interesting physical properties but may also lead to new processing methods for ceramic-based materials. For example, in such a material one may realistically expect changes in crystal morphology and physical properties such as thermal stability and resistance to crystal fracture. In our concept of a molecularly di
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