Design of a mass transport surface utilizing peristaltic motion of a self-oscillating gel

Novel conveyer gels exhibiting autonomous peristaltic motion without external stimuli were prepared by copolymerizing temperature-responsive N-isopropylacrylamide (NIPAAm), ruthenium tris(2,2'-bipyridine) (Ru(bpy) ₃) as the catalyst for the Belousov-Zhabotinsky (BZ) reaction, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). When the gel was immersed in the catalyst-free BZ solution, the BZ reaction occurred in the gel and the chemical wave propagated followed by the peristaltic motion of the gel. In this study, we investigated the influence of the AMPS feed ratio on the network structure and the swelling-deswelling properties of the poly(NIPAAm-co-Ru(bpy) ₃-co- AMPS) gels. The gel had a microphase-separated structure when the AMPS feed ratio was less than 5 mol % due to the effect of the poor solvent in the polymerization process. On the other hand, when the AMPS feed ratio is more than 10 mol %, the gel is a homogeneous structure. The microphase-separated structure highly improved the swelling-deswelling kinetics and generated a swelling-deswelling amplitude of more than 10% of the gel thickness, which was approximately 10 times larger than that of the gel with a homogeneous network structure. Further, we attempted to transport an object by utilizing the peristaltic motion of poly(NIPAAm-co-Ru(bpy) ₃-co-AMPS) gels. A cylindrical poly(acrylamide) (PAAm) gel was transported on the gel surface with the propagation of the chemical wave when the AMPS feed ratio was low (less than 2.5 mol %). We have proposed a model to describe the mass transport phenomena based on the Hertz contact theory, and the relation between the transportability and the peristaltic motion was discussed. It was found that the microphase-separated structure of the gel had an important role for mass transport phenomena.