Silane-Technology
Silane-Technology as the key to chemical nanotechnology
One basic problem in using inorganic nanoparticles and their functions in organic lacquer systems, is their incompatibility with one another. Ionic bonds encounter covalent bonds, or salts encounter molecules and/or organic polymer structures.
The occurring physical effects often can’t dominate the strongly aligned bond types, so that it inevitably results in the amalgamation and/or agglomeration of the inorganic particles. Furthermore, the particles, which are incorporated only as a bulking agent in the organic matrix, have a certain amount of mobility, which results in effects such as aging. The so-called silane offers one solution for this problem.
The base atom of a silane is silicon (Si). Silicon is in the 4th main group, directly under carbon with the atomic number 14. Silicon is a classic metalloid and exhibits both the properties of metals as well as nonmetals. Pure, basic silicon possesses a gray-black color and exhibits a typical metallic, often bronze to bluish sheen. In its oxidized form, silicon appears as SiO2 and is renowned as the main component in sheet glass. As an element, silicon is unique, because along with the ionic bonds, it can also react in stable covalent bonds with carbon, even under normal conditions. These bonds, known as organosilanes, can be used as “bridge molecules” between organic and inorganic chemistry.
On the one hand, the silicon can react by a splitting off of the OR groups, which are generally ethoxy- or methoxy leaving groups, as well as with other silanes, or even react with inorganic bonds or surfaces. The inorganic reaction of silanes to the network formation or to the creation of nanoscale structures or particles normally takes place as hydrolysis and condensation processes of silanes are referred to as the sol-gel-process.
Sol-gel-process
Materials obtained by the sol-gel-process, in which covalent organic groups can be integrated into an inorganic network, are referred to as inorganic-organic composites. These are obtained by hydrolysis and condensation reactions, for example, based on modified silicon alkoxides. One has the following model of a partial step in hydrolysis (4) and condensation, based on the example of methyl trialkoxysilane:
Through the condensation process (5), one obtains a three-dimensional network with an organically modified inorganic framework, the properties of which can be determined, depending on the type of organic residue, by the process. The controllable fiber dimensions of the inorganic-organic components normally lie in the molecular – to nanometer range (≤ 5 nm).