  Via computer simulations, we demonstrate how a densely grafted layer of
polymers, a {\it brush}, could be turned into an efficient switch through
chemical modification of some of its end-monomers. In this way, a surface
coating with reversibly switchable properties can be constructed. We analyze
the fundamental physical principle behind its function, a recently discovered
surface instability, and demonstrate that the combination of a high grafting
density, an inflated end-group size and a high degree of monodispersity are
conditions for an optimal functionality of the switch.
