Polymer brush
Polymer brushes are copolymers that are grafted so densely that the individual polymer chains have to stretch away from the substrate.
physics
Grafted polymers show a rich phase behavior :
- The brushes swell and stretch in a good solvent .
- In the bad solvent, the brush shrinks, possibly so much that the closed film tears open. Depending on the graft density, a structured surface is created from individual or connected clusters.
- Two-component brushes made from immiscible polymers show a pattern in the closed brush.
Use of polymer brushes
The surface properties changed by the polymers are of interest for the application. However, this is still a very new area of materials technology, so that there are not many implemented applications, most of the applications mentioned below are still the subject of research.
- Stabilization of colloids
- This makes use of the fact that the polymer brushes in a good solvent form a barrier against the penetration of other brushes or large molecules. The reason for this is the sharp decrease in entropy when the brush has less accessible volume.
- Change of surfaces from hydrophobic to hydrophilic character
- The mostly polar dyes and lacquers adhere poorly or not at all to the mostly non-polar plastics. On the other hand, the adsorption of proteins on polymer surfaces should often be prevented: In some implants, such as artificial heart valves or dialysis machines, the adhesion of proteins or cells impairs their function.
- Prevention of cell film adhesion
- In most cases, the growth of cell films should be suppressed or prevented, as these films can lead to corrosion of the surface, clog pipes, and release toxic substances into drinking water pipes. Polymer brushes are also being tested to prevent fouling .
- Biocompatibility
- In the field of medical technology, there is the possibility of coating the surfaces of implants in such a way that they do not appear foreign to the cells of the surrounding tissue. This is important for prostheses , for example , where the body's rejection reaction must be prevented.
- lubricant
- Another interesting property is the low friction between two brushes in a good solvent, e.g. B. could be exploited in artificial joints.
Individual evidence
- ^ ST Milner: Polymer brushes. In: Science. Volume 251, Number 4996, February 1991, pp. 905-914, doi : 10.1126 / science.251.4996.905 , PMID 17847384 .