Self-Oscillating Polymer Gels as Novel Smart Materials
- PDF / 426,101 Bytes
- 12 Pages / 432 x 648 pts Page_size
- 56 Downloads / 247 Views
Self-Oscillating Polymer Gels as Novel Smart Materials Ryo Yoshida Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
ABSTRACT As a novel biomimetic polymer gel, we have been studying polymer gels with an autonomous self-oscillating function, since firstly reported in 1996. For developing the polymer gels, we utilized oscillating chemical reaction, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer gel is composed of a poly(Nisopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous swelling-deswelling changes (in the case of gel) or cyclic soluble-insoluble changes (in the case of an uncrosslinked polymer) without any on-off switching of external stimuli. Several kinds of functional material systems utilizing self-oscillating polymers and gels such as biomimetic actuators, mass transport surface, etc. are expected. Here recent progress on self-oscillating polymers and gels and the design of functional material systems are summarized. INTRODUCTION Many researchers have developed several kinds of stimuli-responsive polymer gels that exhibit a reversible swelling-deswelling change in response to environmental changes such as solvent composition, temperature, pH change, etc. In contrast, we have developed a novel polymer gel that cause autonomous mechanical oscillation without an external control in a completely closed solution. In order to realize the autonomous polymer system, we focused on the Belousov-Zhabotinsky (BZ) reaction, which is well-known for exhibiting temporal and spatiotemporal oscillating phenomena [1,2]. We attempted to convert the chemical oscillation of the BZ reaction into a mechanical change in gels and generate an autonomous swelling-deswelling oscillation under non-oscillatory outer conditions. A copolymer gel consisting of N-isopropylacrylamide (NIPAAm) and ruthenium tris(2,2’-bipyridine) (Ru(bpy)3) was prepared. Ru(bpy)3, acting as a catalyst for the BZ reaction, is pendent to the polymer chains of NIPAAm. Poly(NIPAAm) is a well known thermosensitive polymer which exhibits a lower critical solution temperature (LCST) of approximately 32 °C, and the homopolymer gel undergoes a volume phase transition at that temperature. For the poly(NIPAAm-co-Ru(bpy)3) gel, the oxidation of Ru(bpy)32+ moiety causes not only an increase in the swelling degree of the gel, but also a rise in the volume phase transition temperature. As a result, it is expected that the gel will undergo a cyclic swellingdeswelling change when the Ru(bpy)3 moiety is periodically oxidized and reduced under constant temperature.
61
When the poly(NIPAAm-co-Ru(bpy)3) gel is immersed in the catalyst-free BZ solution, a reaction occurs in the gel by the catalytic function of the polymerized Ru(bpy)
Data Loading...
