Organic-Inorganic Hybrid Materials Processing And Applications
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ABSTRACT Hybrid materials as inorganic-organic nanostructured composites require tailored surface chemistry in order to obtain a homogeneous distribution of the nanoparticles in the matrix. For this reason, nanoparticles with organic functions have been synthesized, first, to provide the desired ý-potential at a given pH value, second, to avoid irreversible agglomeration due to the spacing effect, and third, to provide the appropriate surface chemistry. I could be shown that using this approach, it is possible to switch the Q-potential of SiO2 nanoparticles from a negative to a positive potential at neutral and to bind DNA fragments to the particles for an effective transfection into cells. Other examples show that nanoparticles (TiO 2, SiC 2) coated with epoxy and methacryloxy groupings can be used as coating sol for the fabrication of thin films with green densities up to 67 % by volume only by photochemical crosslinking of the polymerizable groupings. Using this approach, interference layers have been fabricated on transparent plastics. In soft matrices, these particles permit to establish appropriate 4-potentials and in electric fields by electrophoresis, it was possible to up-concentrate them to form gradient index optics. The investigations show that surface chemistry-tailored nanoparticles are a useful tool for the fabrication of nanocomposite hybrids. INTRODUCTION Inorganic-organic hybrid materials synthesized by the sol-gel process have gained high impor-
tance during the last fifteen years. First interesting industrial applications have been reported for transparent scratch-resistant coatings [1]. Many papers have been published with very special functions such as glazing systems [2, 3, 4, 5]. The vast majority of hybrid materials are
based on organofunctional silanes, which contribute to the inorganic backbone and at the same time play the role as a carrier of organic functions. Materials based on this approach are ORMOSILs [6]. The use of reactive groupings in organofunctional silanes (epoxides, methacrylates, amines in connection with epoxides or anhydrides) leads to an additional crosslinking, and the formation of inorganic as well as organic backbones at the same time [7]. The use of alkoxides of elements outside Si (alumina, zirconia, titania) in combination with silanes may lead to different levels of "inhomogeneity" or phase separation depending on the processing routes. There are hints that the level of phase separation is very low, close to the molecular or oligomeric state [8], but it is also indicated that the phase separation may reach
the nano level [9, 10]. The vast majority of this literature is devoted either to mechanisms of molecular chemical reactions (mainly investigated by NMR) or materials properties such as mechanical properties [11, 12, 13, 14] or functional properties. Surprisingly low attention is paid to the colloidal part of these systems which always play an important role if phase separation to particulate systems takes place. In these cases, surfaces and interfaces are c
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