A model of a homopolymer brush as a switch

We present a simple model of a densely grafted homopolymer brush with a small fraction of chains extended with solvent-responsive monomers that acts as a switch. On the basis of a simple free energy description, we describe the on and off states of the switch brush, where the switch between states is driven by a change in solvency for the solvent-responsive monomers. These solvent-responsive monomers reside at the brush surface, exposed to solvent, in an on state but are sequestered within the dense brush, sheltered from solvent contact, in an off state. The model considers persistent-on states where the responsive monomers form globules, micelles, and pancake layers at the brush, surface under poor solvent conditions. These persistent-on states decrease the sensitivity of the switch to solvent, but they also increase the signal when the switch, is activated. We describe the on and off states, as well as the switch sensitivity and signaling, over design parameters that include the size of the homopolymer chains and solvent-responsive blocks, and the fraction of chains appended with these responsive monomers.