Inorganic oxide network

Figure 9.1. Scheme of micelle templating. The circular objects correspond to micelles and the gray color to the condensed inorganic oxide network. 

Miao Z, Ding K, Wu T, Liu Z, Han B, An G, Miao S, Yang G (2008) Fabrication of 3D-networks of native starch and their application to produce porous inorganic oxide networks through a supercritical route. Microporous and Mesoporous Materials 111 104-109. 

Metal alkoxides of silicon, titanium, zirconium, and aluminum have been used to prepare optically transparent composite films with the etheric phosphazene polymer poly[bis(2-(2-methoxyethoxy)ethoxy)-phosphazene] (MEEP). Dynamic mechanical and stress-strain techniques are used to evaluate and compare the mechanical properties of the different composites. Despite strong interactions with the inorganic oxide network, the glass transition temperature (Tg) of MEEP does not shift to higher temperature upon addition of the inorganics, but the polymer is reinforced by the oxides. The addition of potassium triflate to the composites resulted in materials with both excellent mechanical properties and increased conductivity. 

Thermal—Oxidative-Resistance Coatings. The thermal stabihty of coatings produced by either covalendy or noncovalendy incorporating 2,4-dinitroaniline into an inorganic siUcate network and coating it onto a sapphire substrate has been examined (67). Although some increase in the thermal... 

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

If R can react with itself or additional components (R contains vinyl, methacryl or epoxy groups, for example), the result of the condensation process is a flexible network of inorganic oxide covalently bonded to organic polymers, namely a hybrid nanocomposite lacking interface imperfections. The properties of this hybrid nanocomposite are intermediate between those of polymers and glasses, and can meet unique requirements. 

The hybrids generated by the sol-gel process combine the flexibility and mechanical strength of the organic constituent with the hardness, stiffness and transparency of the inorganic silica network. Hardness is often further conferred by the employment of other inorganic oxide particles (such as alumina or titania). This first started in the 1980s when... 

Condensation or precipitation The species that are so formed may be unstable and in a second step may condense upon elimination of molecules such as ROH or H20, thus leading to the formation of a hydroxide or oxide network. This step corresponds to an inorganic polymerization such as (9) ... 

The sol-gel process is the name given to a number of processes in which a solution, or sol, undergoes a sol-gel transition. In this broadest sense, the term sol-gel refers to the preparation of inorganic oxides by wet chemical methods, irrespective of final form product—monolith, crystalline, or amorphous (1). Using sol-gel materials for mechanical entrapment of enzymes permitted stabilization of the proteins, tertiary structure owing to the tight gel network (2). Moreover, the easy insertion of substituent groups into... 

The characteristic features of some types of loop are associated with certain well-defined pore structures. Thus, Type HI loops are given by adsorbents with a narrow distribution of uniform pores (e.g. open-ended tubular pores as in MCM-41 - see Section 12.3.1). Many inorganic oxide gels give the more common Type H2 loops. The pore structures in these materials are complex and tend to be made up of interconnected networks of pores of different size and shape. 

Organic species can also be chemically bonded to the oxide network via Si-C bonds. Many organoalkoxysilane precursors, R4 Si(OR), are commercially available. They contain nonhydrolyzable Si-C bonds, so that organic moieties are not removed upon hydrolysis. Depending on the nature and amount of organic and inorganic components, it becomes possible to tailor the microstructure and even obtain multifunctional materials. 

Schematic representation of the chemical modifications of the silicon oxide network. Inorganic modification with M = Al, Ti, Zr and others, organic modification with R = alkyl, aryl, both without and with additional functional groups, for example fluoroalkyl, or R = bioactive or dyestuff group. 

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