Self-organization in Polymer Gel Systems Incorporated with Active Elements

通过将钌（Ru（bpy）3）共价键合到聚N-异丙基丙烯酰胺（PNIPA）分子链上，制备了与Belousov-Zhabotinsky（BZ）反应偶联的PNIPA凝胶。发现BZ反应中的化学振荡引起凝胶的周期性和自主的溶胀-收缩体积变化。相反，在这种新型凝胶中，PNIPA凝胶的体积变化影响化学波的传播。我们的注意力集中在化学波的机械变化的影响，通过利用热驱动的体积相变的PNIPA凝胶。化学波的速度和频率均随温度的升高而增大，在凝胶的体积转变温度处突然减小。随着温度的升高，对波传播至关重要的HBrO_2的扩散受到阻碍。在低温区，HBrO_2通过凝胶网络的扩散与惰性分子在受限环境中的简单扩散相同。相反，在高温下，波速的变化不能用简单的扩散理论来解释。这可能是因为反应物浓度的不均匀性和大体积催化剂量的增加阻碍了扩散和反应速率。根据还原剂与氧化剂的浓度比，还原波与通常的氧化波相反。观察到的最引人注目的行为是自我复制和还原脉搏波的保存。在前一种动力学中，在传播的还原脉冲波消失之后，它分裂成两个反向传播的脉冲。在后一种动力学中，反向传播的还原脉冲波在迎面碰撞时相互湮灭，然后重新出现。

The poly (N-isopropyl acrylamide)(PNIPA) gel coupled with Belousov-Zhabotinsky (BZ) reaction was prepared by covalently bonding the catalyst ruthenium (Ru(bpy)_3) to the polymer chain. The chemical oscillation in the BZ reaction is found to induce periodical and autonomous swelling-shrinking volume changes of the gel. In this new type of gel, conversely a volume change of the PNIPA gel affects the propagation of the chemical wave. Our attention was focused on effects of mechanical changes on the chemical wave by utilizing the thermally driven volume phase transition of the PNIPA gel. Both the velocity and the frequency of the chemical wave increased with increasing the temperature, and abruptly decreased at the volume transition temperature of the gel. The diffusion of HBr0_2, which is essential for the wave propagation, was hindered with increasing the temperature. The diffusion of HBrO_2 through the gel network in the low temperature region was explained in the same way as a simple diffusion of inactive molecules through a restricted environment. At the high temperature, in contrast, the change of the wave velocity cannot be explained by the simple diffusion theory. This is probably because non-homogeneities in reactant concentrations and the increase in the amount of bulky catalyst hinder the diffusion and the rate of reaction.Depending on the ratio of concentration of the reducing agent to that of the oxidizing agent, reduction waves appears in contrast to usual oxidizing waves. The most striking behaviors observed are self-replication and preservation of reduction pulse waves. In the former dynamics, after the propagating reduction pulse wave vanishes, it splits into two counterpropagating pulses. In the latter dynamics, counterpropagating reduction pulse waves annihilate each other upon head-on collision and then reappear.