Rubbery ormosils and their applications

Abstract

When a polymer such as silanol terminated polydimethylsiloxane (PDMS) is mixed with an alkoxide such as tetraethoxysilane (TEOS) in a suitable solvent and catalyst, gels can be prepared which exhibit rubbery elasticity. The microstructures of such organically modified silicates (ormosils) can be controlled to give solids which are opaque or transparent via experimental variables. This paper describes the conditions for the development of various microstructures, the properties of ormosils and how microstructures can control properties. Reaction mechanisms and structure developments during heating are followed by liquid and solid state NMR studies and electron microscopy. The rubbery ormosils are somewhat unique in that they contain a minor organic component and a major inorganic component, and are therefore potentially useful as a non-toxic rubber at high temperatures. When these ormosils are heat-treated in a non-oxidizing atmosphere up to about 1000°C, decomposition and reorganization take place. Depending on a number of variables, the products can be a black glass or a black porous nanocomposite. The latter can now be heated to 1400°C in air with no loss of carbon and no deformation. The porosity, low-expansion coefficient and black color make these nanocomposites useful as high-temperature insulators. Transparent ormosils are superior to their pure oxide gel counterparts in terms of stress fracture during processing because of the presence of non-linking organic groups. Laser-active organic dyes can be dispersed in ormosil liquid solutions prior to gelation to give transparent solid-state tunable organic dye laser rods or discs. Ultrafine crystals of cadmium sulfide have also been dispersed in ormosils to give optical discs for non-linear applications. The ormosils contain chemical bonds linking organic polymers to inorganic oxide networks. They are likely to be the first group of many new inorganic-organic materials of the future such as multifunctional solids.