Considerations about the sol-gel process: From the classical sol-gel route to advanced chemical nanotechnologies

This paper was given on occasion of receiving the first Life Time Award by the International Society on Sol-Gel Science and Technology. Its intention is to provide an insight on the development of this field, its driving forces and especially on its impact on application and industrial technologies. The motivation of the work carried out in the last decades is that in the early days of the sol-gel technologies, where this route started to interest industry as well as scientists, the author got interested in a field which was clearly application-driven and strongly anchored in the material scientist community rather than in fundamental chemistry. If one is talking about application-oriented technologies, of course, markets and industrial needs have to be taken into consideration, because the restrictions or bottle-necks, but also chances provided by economical needs strongly may govern the field. In opposition to these fields, only driven by science, may not have these restrictions as far as it is possible to raise funds for the scientific work. For this reason, the attempt is made to point out the connections between application and science in the sol-gel field. Since I am working in the sol-gel field since 1975, strongly focused on industrial applications, it should be understandable that many of my own development examples are used to demonstrate this way. Another problem, of course, is connected to the sol-gel field: This is a question of appropriate definitions as well as to draw a clear borderline of the field. Especially in the last decade, the connection of sol-gel materials to nanostructured materials has become closer, so that it is difficult to clearly divide these fields. On the other hand, the fabrication of nanoparticles by hydrolysis and condensation processes or controlled precipitation processes can be defined as a sol-gel technology, but in many cases is just not done. This leads to the fact that in many areas, sol-gel types of processes are used, but called different. Due to the fact that the properties of small particles either in solution or dispersed in an appropriate matrix show highly interesting material properties, it would be desirable that the sol-gel community would try to interact stronger with these developments (e.g. the "particle" community). This also might include a focus of the sol-gel area a little bit more back to the routes, to material science development and engineering. According to my opinion, this would be a very interesting supplement for the field as it is represented today.