One particularly interesting feature of polymer brushes arises from their flexibility: While the chains are attached to the substrate at one end, the remaining end remains fully flexible. It is possible to modify a certain amount of chain ends by attaching a specially designed end-group or nanoparticle, which interacts with the solvent in a different way than the host polymers. If the brush is immersed into a good solvent, but for the modified chain ends the same solvent is poor, then these ends are diving into the brush. A change of the temperature modifies their excluded volume and thereby creates a switchable surface with chemical properties as defined by the end-groups. We have shown that in the case of high grafting densities and highly monodisperse brushes a surface instability arises which can be used to amplify such a switching process.Switchable surfaces are easily generated with the help of binary brushes (see the animation in the introduction). If one polymer species is hydrophobic, the second hydrophilic, then a vertical phase segregation occurs that, upon change of solvent, is used to reversibly switch the two polymer layers.

Highlights:

1. Holger Merlitz, Gui-Li He, Chen-Xu Wu, and Jens-Uwe Sommer
   Nanoscale brushes: How to build a smart surface coating
   Phys. Rev. Lett. 102,  115702 (2009)
2. Petra Uhlmann, Holger Merlitz, Jens-Uwe Sommer, and Manfred Stamm
   Polymer brushes for surface tuning
   Macromolecular Rapid Communication 30, 372 (2009)
3. Holger Merlitz, Gui-Li He, Chen-Xu Wu, and Jens-Uwe Sommer
   Surface Instabilities of Monodisperse and Densely Grafted Polymer Brushes
   Macromolecules (Note) 41, 5070 (2008)
4. Holger Merlitz, Gui-Li He, Jens-Uwe Sommer, and Chen-Xu Wu,Reversibly
   Switchable Polymer Brushes with Hydrophobic/Hydrophilic Behavior: A Langevin Dynamics Study
   Macromolecules  42, 445 (2009)