Research focus

Colloid chemistry
Colloid chemistry includes the synthesis, characterization and modification of colloid-disperse systems. These consist of dispersed solids (colloids) with particle sizes between one nanometer and up to the low micrometer range. Thereby, the particles are evenly distributed as a disperse phase (dispersion). From a thermodynamical point of view, colloidal dispersions with many small particles should coagulate (flocculate) to energetically favoured larger particles. Different forces can work against the colloid particles approaching each other such as electrostatic repulsion, sterical hindrance or the presence of large hydrate shells (hydrophilic colloids).
One of the goals in current research concerning colloidal systems is to construct new materials with interesting properties. For this purpose we here present two examples which are being investigated at the chair for construction chemicals. Water based dispersions of organic particles can be categorized as a colloidal system. Such dispersion are used e.g. in tile adhesives or for coatings of manifold kinds. Through appropriate composition of the chemical constituents for synthesis, the macroscopic materials properties of the coating or the adhesive can be tailored. Thereby, the combination of inorganic and organic particles is of special interest. Fig. 1 shows an ESEM (Environmental Scanning Electron Microscopy) recording of a styrene-butylacrylate dispersion, which is about to coalesce to a film due to water removal.


Fig. 1:  Coagulating polymer dispersion.

Fig. 2: Sol-gel process.

A further, promising method for the construction of new materials is represented by the sol-gel process (Fig. 2). In this process reactive components slowly condensate as a sol (colloid) to form a fixed cross-linked gel which initially still contains a lot of liquid phase. The sol-gel process is used e.g. to synthesize highly pure clinker phases (cement phases) for basic research.
The stability of colloid disperse systems can be monitored well with the help of zeta potential measurements. The chair has a zeta potential device at their command, which allows the investigation of concentrated systems having water to solid ratios of up to 0.3. The device works by the electroacoustic principle.