Formation of Ordered Silica-Organic Hybrids by Self-Assembly of Hydrolyzed Organoalkoxysilanes with Long Organic Chains
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Formation of Ordered Silica–Organic Hybrids by Self-Assembly of Hydrolyzed Organoalkoxysilanes with Long Organic Chains Kazuyuki Kuroda1, 2 and Atsushi Shimojima1 1
Department of Applied Chemistry, Waseda University,
Ohkubo-3, Shinjuku-ku, Tokyo 169-8555, Japan 2
Kagami Memorial Laboratory for Materials Science and Technology, Waseda University,
Nishiwaseda-2, Shinjuku-ku, Tokyo 169-0051, Japan ABSTRACT
Various layered hybrid films prepared from organoalkoxysilanes with long organic chains, based on the self-assembly of the hydrolyzed species, are reviewed. Morphological control of transparent and oriented films was achieved by cohydrolysis and polycondensation with tetraalkoxysilanes, followed by dip- or spin-coating. In addition to alkyltrialkoxysilanes, alkyldimethylmonoalkoxy- and alkylmethyldialkoxy-silanes were also used as the structural units, implying that the inorganic–organic interface can be designed at a molecular level. In these cases, co-condensation in the precursor solution plays an essential role in the formation of homogeneous and ordered films. Alkenyltriethoxysilanes with terminal C=C bonds were also employed to prepare layered hybrid films. Interlayer chains were polymerized upon UV irradiation, and the resulting films exhibited a significant increase in the hardness if compared with the films before polymerization. Hybrid films thus obtained are a new class of materials and of great interest for a wide range of materials chemistry. INTRODUCTION Organoalkoxysilanes are widely used as structural units to construct a variety of silica-based hybrid materials [1–3]. Because simple sol–gel reactions of alkoxysilanes usually result in the formation of amorphous materials [4], much efforts have been made in the structural control on a nanometer-length scale [5–8]. Such an attempt is of great interest from the possibility to produce novel hybrid materials with unique structures and V2.8.1
properties. Self-organization of organosilane molecules is a promising technique for the construction of ordered hybrid materials. The process relies on the amphiphilic nature of hydrolyzed organosilane molecules containing both hydrophilic silanol groups and hydrophobic alkyl chains. While many studies have focused on the interfacial deposition of alkylsiloxane monolayers [9], researchers have recently shown that the process can be extended to the formation of multilayered hybrids by the reaction in solution states [10–12]. We reported the formation of multi-bilayer aggregates by hydrolysis and polycondensation of alkyltrialkoxysilanes in homogeneous solutions [12]. These are a new class of layered materials consisting of organic two-dimensional arrays and siloxane networks linked by covalent Si–C bonds. Although the layered hybrids derived from alkyltrialkoxysilanes are obtained as powders, transparent and oriented thin films can be obtained by cohydrolysis and polycondensation with tetraalkoxysilane under well-controlled conditions [13].
This
synthetic approach can be extended to the development of a varie
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