Height-Switching of Active Polymers in Binary Polymer Brushes

Modifying surface properties by polymer brushes is very important in polymer science. The surface properties of binary polymer brushes can be changed by switching the height of one of the two polymers. In this study, the height-switching of the active polymer in a binary polymer brush composed of active and passive polymers was investigated through Langevin dynamics simulations. The active polymer was modeled as a copolymer consisting of an active head possessing a self-propelled force with magnitude Fs and a subsequent passive block. Both the active polymer and passive polymers were end-grafted onto a surface that exhibits an attraction to the active polymer but pure repulsion to the passive polymers. The active polymer is adsorbed on the surface at low Fs while it is desorbed at large Fs. The alteration of the state of the active polymer leads to the reversible height-switching of the active polymer, specifically, the switch between the immersed state of the active polymer beneath the polymer brush at small Fs and the exposed state of the active polymer protruding out of the polymer brush at large Fs. The dependence of the critical self-propelled force Fs* for this height-switching on the length of the active polymer and the grafting density of the polymer brush was investigated. The results show that active polymers have significant potential as candidates for smart polymer brushes.