Binary polymer brushes with hydrophobic/hydrophilic behavior are forming a two-layer system with a collapsed hydrophobic and a swollen hydrophilic phase. The process of switching upon Sudden change of he solvent quality is analyzed in detail for Various solvent selectivities, chain lengths, and grafting densities. This process is highly reversible since after a microphase separation the chains are moving collectively inside their phase domains so that the interactions between chains of different species are diminished. The thickness of the collapsed layer does not scale linearly with the chain length N, an unexpected result which is discussed in the paper. The switching relaxation times display a scaling of N-2 like Rouse relaxation and not of N-3 like vertical relaxation times in equilibrium.