Sol-gel synthesis of biocompatible silica-chitosan hybrids and hydrophobic coatings
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RTICLES Sol-gel synthesis of biocompatible silica-chitosan hybrids and hydrophobic coatings S. Smitha, P. Shajesh, P. Mukundan, and K.G.K. Warriera) Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (Formerly Regional Research Laboratory), Council for Scientific and Industrial Research (CSIR), Trivandrum 695019, Kerala, India (Received 6 October 2007; accepted 4 January 2008)
A new organic–inorganic hybrid synthesized through a sol-gel process starting from alkoxysilane and chitosan is reported. Functionalization of the hybrid was effected through in situ hydrolysis–condensation reaction of methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS) in the reaction medium. The process yields highly transparent and hydrophobic silica–chitosan hybrids. The hybrid gel was investigated with respect to chemical modification, thermal degradation, hydrophobicity, and transparency under the ultraviolet-visible region. The extent of hydrophobicity had been tailored by varying the precursor ratio. SiO2–chitosan–MTMS hybrids showed a higher thermal stability than SiO2–chitosan–VTMS (SCV) hybrids with respect to hydrophobicity. Condensation of silsesquioxanes generated from the hydrolysis of MTMS and VTMS over the silica-chitosan particles impart hydrophobicity to the hybrid. The coatings of functionalized SiO2–chitosan precursor sol on glass substrates showed nearly 100% optical transmittance in the visible region. The present hybrid material may find application in optics and other industries.
I. INTRODUCTION
Organic–inorganic nanocomposites containing various polymers have found applications in optical coatings, high refractive index films, contact lenses, thin film transistors, optical waveguides, adsorbents, catalysts, and high-energy fields.1–5 Organic polymers have properties such as flexibility, low density, toughness, and easy formability, whereas ceramic materials have good mechanical and optical properties. Organic polymers can be combined at the nanoscopic scale with inorganic materials such as silica and titania to create a new class of high-performance, highly functional organic–inorganic hybrid materials.6 Polymethylmethacrylate (PMMA), polyethylene oxide, polycaprolactone, polystyrene, and acrylic polymers are some organic polymers used for the synthesis of organic–inorganic hybrid materials.7–11 Biopolymers such as gelatin, chitosan, cellulose, and alginates are suitable candidates for the organic counterpart in such materials because of their low cost, non toxicity, biocompatibility, and multifunctional properties.12,13 These hybrid materials are biocompatible and have been used as bone substituents, cements for bone repair and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0271 J. Mater. Res., Vol. 23, No. 8, Aug 2008
reconstruction, and also for immobilization of cells and enzymes.13,14 These materials have also found application in catalysis and sensors.15,16 Silica is the most widely investigated inorga
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