Grafting techniques have advantages over other approaches to create thin functional films because of several reasons. They include easy and controllable introduction of polymer chains with a high surface density, precise localization of the chain at the surface, and long stability of the grafted layers. The use of polymer brushes is on the one hand a very promising mean to create those new surface functionalities as switchability or response to environmental conditions and on the other hand an effective manner to tune the relevant surface properties for many applications, as wettability, adhesion, lubrication, friction, biocompatibility or, for particles, colloidal stability. The factors influencing synthesis and properties of such layers were the subject of numerous experimental and theoretical studies during the last years. Generally the behavior of those ultrathin polymeric layers is strongly dependent on the grafting density, the molecular weight and chemical composition of the polymer chains. Linear polymer chains grafted on the surface are gaining a brush like conformation if the distance of the chains is becoming smaller than the double of the radius of gyration of the macro molecules. In this case the polymer chains are taking a conformation stretched away from the surface because of excluded volume effects.
Heterogeneous binary polymer brushes, which are experimentally investigated only recently, are created by grafting two incompatible polymers one after the other on the surface. The covalent bonds to the substrate are preventing that the polymer film is separating macroscopically into the two polymer components. Those films have shown to be a versatile tool to create, in dependence on the grafting density, stable homogeneous or flexible responsive functional coatings. In the latter case it is possible to switch the surface properties of the film between the properties of two incompatible polymers by external stimuli, as e.g. temperature, solvent, electrical field, pH value.

For the fabrication of binary brushes grafting from“ (as radical polymerisation at the interface) and „grafting to“ (as tethering of the polymer chains from solution) methods were developed and investigated in detail.
The amplification of the amplitude of switching (from superhydrophilic to ultrahydrophobic) by creating hierarchically structured surfaces was investigated as well as the creation of switchable surface structures by environmental responsive lithography. Binary polymer brushes can also be used to create thin films with gradients of the layer thickness or even switchable gradients of surface hydrophobicity/ hydrophilicity.

A very interesting task is also the interaction of polymer brushes with nanoparticles and proteins. The interaction of globular model proteins with mixed polylelectrolyte brushes, i.e. brushes composed of two oppositely charged polyelectrolytes was investigated in dependence pH and buffer salt concentration, and the adsorption mechanism was studied in detail. So called “counter ion evaporation” seems to be a major driving force for protein adsorption on mixed polyelectrolyte brushes under certain conditions.