Preparation of Optically Transparent Films of Poly(methyl methacrylate) (PMMA) and Montmorillonite
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Preparation of Optically Transparent Films of Poly(methyl methacrylate) (PMMA) and Montmorillonite Elena Vasiliu1, Chyi-Shan Wang1,2, and Richard A. Vaia3 1 Department of Chemical and Materials Engineering, University of Dayton, Dayton OH 45469 2 University of Dayton Research Institute, Dayton OH 45469 3 Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433 ABSTRACT Transparent polymeric material with enhanced thermal, mechanical and barrier properties are of special interest for advanced structural, optical and photonic applications. The present paper reports a novel solution processing scheme for fabricating optically transparent polymer nanocomposites involving organophilic layered silicates. It is shown that the nanocomposite material prepared with PMMA and an organically modified montmorrilonite maintains the excellent optical transparency of PMMA. Small-angle x-ray scattering of the polymer nanocomposite material does not show any Bragg’s reflection of the organophilic layered silicate. The optical transparency of the nanocomposite material is attributed to a high degree of exfoliation of the montmorrilonite in the polymer matrix. INTRODUCTION Organic and inorganic fillers are commonly used to enhance polymer performance. Among the various inorganic fillers, nanoscale layered silicates, which have a sheet-like structure and an extremely large surface area (700 m2/g vs. 150 m2/g for carbon black) [1], are especially attractive for conferring thermal, mechanical and barrier properties to polymeric materials for specific applications. The organic affinity of the nanophase fillers can be modified by cation exchange with organic salts to tailor the structure and properties of the resulting polymer composite material. Individual platelets of nanoscale layered silicates have a length scale smaller than the wavelength of visible light. As a result, they may be used to reinforce organic polymers such as PMMA and polycarbonate without significantly degrading their optical clarity. The transparent polymer nanocomposite material has potential for advanced applications in protective coatings, windows, and integrated optical devices [2]. In order to achieve the maximum reinforcement of the layered silicates, their unit layers must be uniformly dispersed in the polymer matrix and have strong interaction with the polymer [3]. Various methods, such as solution mixing [4,5], melt mixing [6,7], and in-situ polymerization [8,9], have been used to disperse layered silicates into organic polymers. However, except a very few cases [9,10], results are usually a composite material containing both intercalated and exfoliated layered silicates. Normally, such a phase-separated composite material does not lead to significant improvement in thermal, mechanical and barrier properties over its host polymer. The only system that exhibits dramatic property improvement is the nylon 6-montmorrilonite nanocomposites obtained by in-situ polymerization. This composite material contains highly exfoliated montmorrilonite unit laye
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