Design of Self-Oscillating Polymer Brushes and Control of the Dynamic Behaviors

A polymer brush surface with autonomous function has been designed by using a self-oscillating polymer that we developed. The self-oscillation is induced by chemomechanical energy conversion from an oscillating chemical reaction (the Belousov-Zhabotinsky (BZ) reaction) to conformational changes of polymer chains. In this study, the surface nanostructure of polymer brushes were regulated and the spatiotemporal behaviors of self-oscillation were investigated. The target polymer brush surfaces were prepared through surface-initiated atom transfer radical polymerization (SI-ATRP) of N-isopropylacrylamide (NIPAAm) and N-(3-aminopropyl) methacrylamide (NAPMAm), and the subsequent conjugation of Ru(bpy)₃ to the amino group of NAPMAm. The characterization of the prepared polymer brush and the free polymer was determined by X-ray photoelectron spectroscopy, atomic force microscopy, attenuated total reflection Fourier transform infrared spectroscopy, UV-vis spectrophotometry, gel permeation chromatography, and ¹H NMR. Their dynamic properties were estimated by quartz crystal microbalance with dissipation and fluorescence microscopy. The amounts of Ru(bpy)₃ immobilized to polymer brush surfaces could be controlled by adjusting the reaction conditions of SI-ATRP and conjugating Ru(bpy)₃. Importantly, an appropriate structure of polymer brush to give stable oscillation has been indicated from image analysis of chemical wave propagation. Further, several physicochemical parameters to control the oscillating behaviors, including the rate constant of the autocatalytic reaction, the diffusion constant of the activator, and the activation energies for the reaction and diffusion, have been obtained from theoretical consideration. These results will be helpful for developing subsequent applications such as autonomous transport systems.