| Research Abstract |
Submicron-sized poly(N-isopropyl acrylamide) (PNIPA) gels immobilized the ruthenium catalyst (Ru(bpy)_3^<2+>) of Belousov-Zhabotinsky (BZ) reaction was prepared by emulsification polymerization. We constructed of an ensemble consisting of many Ru(bpy)_3^<2+>-co-PNIPAM micro gel particles by an optical trapping using Nd^<3+>: YVO_4 laser. A particle of ca. 5μm in diameter was formed above a certain laser power. We observed an oxidized wave propagating on the trapped particle.
We created a copolymer (Ru(bpy)_3^<2+>-co-PNIPAM) showing rhythmical and reversible coil-globule (CG) transitions by covalently bonding Ru(bpy)_3^<2+> to PNIPAM. A transmittance through its BZ solution showed the oscillation profiles with the period of 60 s at 22℃. We confirmed that this phenomenon is related to the rhythmical CG transition by using a dynamical light scattering. When a polymer solution was irradiated with an IR laser beam, a soft network structure of ca. 5μm in diameter was produced in the vicinity of the focal spot. This structure showed a rhythmical change with the BZ reaction.
Dynamical responses of a Ru(bpy)_3^<2+>-doped microgel to external forcing including noise were investigated. In an oscillatory system, when a subthreshold periodic signal and noise were simultaneously imposed on the oscillator, stochastic resonance manifested itself in the form of noise-enhanced phase locking. These experimental findings were qualitatively reproduced in the numerical simulation with a forced Oregonator model . In the excitable system, when a noise amplitude was increased above a certain value, and oscillatory state appeared. We showed the evidence of coherence resonance by using various statistical quantities. We demonstrated that, at an optimal noise level, the period of coherent oscillation is determined by the time scale of the intrinsic dynamics of the system.
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