Colloid Chemistry - Prof. Koetz

Colloids in profile area "soft matter"

What does colloid chemistry actually have to do with "soft matter"?

Colloid derives from the Greek word "colla" (glue). According to Thomas Graham (1861) one calls glue-like substances, which diffuse very slowly as colloids. Accordingly, colloids are assigned a priori to "soft matter", or better "glue-like" matter.

Over the last 150 years, however, the term colloid has undergone a major transformation. According to Wolfgang Ostwald, colloids are tiny particles or droplets of a substance (with particle diameter smaller than 500 nm) which are evenly distributed in a dispersant. Due to the extremely small particle size, such nanostructured systems have extremely large surfaces. Thus, the particle surface in a volume of only one liter can exceed the size of several football stadia. This implies completely new property profiles and opens up new fields of application.

The first "researchers" who produced nanoparticles were the alchemists. Without understanding the mechanism of the method of production, they produced colored gold dispersions (gold tinctures), which were used as "life-elixirs", but without success, as we know today!

The aim of current research strategies is to produce and use such nanostructured systems with defined particle dimensions in a targeted manner.

Nature shows us an extremely interesting way by structuring inorganic matter through the use of self-organizing phenomena through biological processes. This process is generally also referred to as biomineralization. Some examples for this are diatoms, nacre, or even bones and teeth. Figure 1 shows an electron micrograph of the highly ordered SiO2 structure of diatoms. As a pre-matrix, nature in these cases requires organic compounds, e.g. carbohydrates and proteins.

Figure 1: TEM-micrograph of the highly ordered SiO2-structure of diatoms.

Trying to adapt the "synthesis strategies" of the nature, a template is needed, that is a pre-matrix on the nanometer scale, which is "self-organized", if possible. Such "self-organization processes" can always be expected when the system has "amphiphilic" properties. Such an attribute profile is characterized, in particular, by surfactants. According to this pattern, nature, for example, builds membrane structures made of phospholipids. In the terminology of the colloid chemist, these are nothing else but self-organized double-layer membranes, which are composed of double-tailed amphoteric surfactant molecules (phospholipids).

Inspired by this principle of nature, our research activities focus in particular on the role of polyelectrolytes in self-assembled surfactant systems. We are interested, on the one hand, in lamellar liquid crystalline systems, i.e., artificial biomembrane systems, and, on the other hand, self-assembled oil / water / surfactant systems and their interaction with charged polymers (polyelectrolytes), and their suitability as a template phase for nanoparticle formation.

The production, characterization and application of nanoparticles of defined shape and size play a central role within the current research.