Research focus

Nanomaterials
Over the past few years, a lot of effort has been put into the preparation and research of nanostructured materials having a variety of different functionalities. The interest in such materials derives from the prevailing dependence of their properties (optical, electrical, catalytical) on size, composition and structure of the surface. Such materials can be of organic („soft-matter“) or inorganic („hard-matter“) nature or also a combination of both. In many cases they are modified with additional functionalities in order to introduce certain properties into the system. In the field of nanomaterials one's attention has greatly been directed towards the synthesis of colloidal materials because these possess a large field of applications and they are especially suitable for functionalizing surfaces, e.g. in pharmaceutics and biology.

In the field of colloidal materials "core-shell" particles represent an interesting field of research because of the possibility to combine different functionalities and to precisely influence the properties through composition, thickness of the core, the shell and the particle size. "Core shell" particles are mostly prepared through so-called heterocoagulation (Fig. 1).

 
Figure 1: Schematic illustration of the synthesis of SiO2@TiO2 by heterocoagulation

In this process the smaller particle is chemical or physically bound to the surface of the bigger particle. This is the case, if it is ensured that both particles possess a sufficiently different surface charge. By measurement of the zeta potential, the particle charge can be determined. The synthesized core-shell particle consists of a core which can exhibit completely different properties than the shell. As already mentioned, this can be used for the specific creation of functional materials. For characterization, apart from zeta potential measurements, electron microscopy (SEM, TEM) is utilized for gaining insight into the morphology and layer thickness of the particle.
At the chair for construction chemicals such core-shell systems are being synthesized and amongst others being characterized by scanning electron microscopy (SEM) (Fig. 2). An example presents titanium dioxide coated silica particles which, when irradiated with sunlight, are capable of developing photocatalytical activity, thus decomposing organic material such as mould, dust, nicotine or biofilms.


Figure 2:   REM picture von SiO2@TiO2 particles