A polymer brush designed to behave as a switch

A polymer brush is a surface to which linear chains are end-grafted to such high densities that the chains stretch away from the grafting surface. These chains retain sufficient conformational freedom to allow a significant conformational response to changes in environmental conditions, such as temperature or solvency. With proper design, these responsive surfaces can respond reversibly to external stimuli and thus act a “switch”. We have designed a polymer brush switch of densely-grafted homopolymer with a small fraction of chains extended with 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. We describe persistent-on states where the responsive monomers from 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 of the switch when it is activated. (WithY.X. Gao)