Affinity Control of Aminopropylsiloxane-based Organic/Inorganic Hybrids for Optical Sensors
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Affinity Control of Aminopropylsiloxane-based Organic/Inorganic Hybrids for Optical Sensors Shingo Katayama, Noriko Yamada1 and Masanobu Awano2 Fine Ceramics Research Association, 2266-98 Shimoshidami, Moriyama, Nagoya 463-8560, JAPAN 1 Nippon Steel Corporation, Advanced Technology Research Laboratories, 20-1 Shintomi, Futtsu, Chiba 293-8511, JAPAN 2 Advanced Manufacturing Research Institute, AIST, 2266-98 Shimoshidai, Moriyama, Nagoya 463-8560, JAPAN ABSTRACT The aminopropylsiloxane-based organic/inorganic hybrid is known as a sensitive material toward NO2 gas for optical sensing systems but it has the irreversible detection. The affinity of the aminopropylsiloxane-based organic/inorganic hybrid toward NO2 gas was controlled by incorporating an Nb inorganic component derived from Nb(OC2H5)5 into the hybrid structure. The amino groups had a strong coordination bond with hydrolyzed Nb(OC2H5)5 and/or an acid-base pair with an oxoanion formed by hydrolysis of Nb(OC2H5)5. Thus, the strong solid-basicity of the aminopropylsiloxane-based organic/inorganic hybrid was weakened. The aminopropylsiloxane-based organic/inorganic hybrid containing an Nb inorganic component provided reversible sensing toward NO2 gas in an optical sensing system. NO2 is thought to be more weakly adsorbed because of the weakened basicity of the amino groups. INTRODUCTION The organosiloxane-based organic/inorganic hybrids have a potential for a variety of applications, such as optical, mechanical, chemical, electrical, biological and other fields. The material design of the organosiloxane-based organic/organic hybrids can be carried out by selecting both the organic group covalently bonded to the siloxane network and the inorganic component incorporated into the organosiloxane network. The organic group used as an organic component is not only the inert components such as alkyl and phenyl groups but also the functional components such as epoxy, vinyl, methcryloly, amino, mercapto, and sulfonic groups. The functional organic components act as an organic network former and play a role of the affinity control toward molecules and ions. Since the amino group has an affinity toward NO2 gas, aminopropylsiloxane-based organic/inorganic hybrid films have been investigated as a sensitive material for optical sensing systems such as Mach-Zehnder interferometer[1] and composite optical waveguide-based polarimetric interferometer[2, 3]. Although the optical sensing system allows the miniaturization, sensitivity improvement and cost reduction of NO2 sensor, the sensitive film of the organic/inorganic hybrid prepared from aminopropylalkoxysilane shows the irreversible detection[1-3]. The amino groups react with NO2, causing a detectable change in the optical properties of the aminopropyl-based organic/inorganic hybrid film, but the reaction is irreversible. The authors have found that the aminopropylsiloxane-based organic/inorganic hybrid modified with an Nb inorganic component provided the reversible detection of NO2 gas[4]. The neutralization effect o
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