Geher-Herczegh Tunde, Wang Zuowei, Masuda Tsukuru, Yoshida Ryo, Vasudevan Nandini, Hayashi Yoshikatsu
Biomedical Sciences and Biomedical Engineering, School of Biological Sciences, University of Reading, Reading RG6 6DH, U.K.
Department of Mathematics and Statistics, University of Reading, Reading RG6 6AX, U.K.
Macromolecules. 2021 Jul 13;54(13):6430-6439. doi: 10.1021/acs.macromol.1c00402. Epub 2021 Jul 2.
We show experimentally that chemical and mechanical self-oscillations in Belousov-Zhabotinsky hydrogels are inherently asynchronous, that is, there is a detectable delay in swelling-deswelling response after a change in the chemical redox state. This phenomenon is observable in many previous experimental studies and potentially has far-reaching implications for the functionality and response time of the material in future applications; however, so far, it has not been quantified or reported systematically. Here, we provide a comprehensive qualitative and quantitative description of the chemical-to-mechanical delay, and we propose to explain it as a consequence of the slow nonequilibrium swelling-deswelling dynamics of the polymer material. Specifically, standard hydrogel pieces are large enough that transport processes, for example, counterion migration and water diffusion, cannot occur instantaneously throughout the entire gel piece, as opposed to previous theoretical considerations. As a result, the volume response of the polymer to a chemical change may be governed by a characteristic response time, which leads to the emergence of delay in mechanical oscillation. This is supported by our theoretical calculations.
我们通过实验表明，贝洛索夫-扎博廷斯基水凝胶中的化学和机械自振荡本质上是异步的，也就是说，在化学氧化还原状态发生变化后，溶胀-消溶胀响应存在可检测到的延迟。这种现象在许多先前的实验研究中都可观察到，并且可能对该材料在未来应用中的功能和响应时间产生深远影响；然而，到目前为止，它尚未得到系统的量化或报道。在此，我们对化学到机械的延迟提供了全面的定性和定量描述，并提出将其解释为聚合物材料缓慢的非平衡溶胀-消溶胀动力学的结果。具体而言，标准水凝胶片足够大，以至于与先前的理论考虑相反，传输过程（例如，抗衡离子迁移和水扩散）不能在整个凝胶片中瞬间发生。因此，聚合物对化学变化的体积响应可能由一个特征响应时间控制，这导致了机械振荡中延迟的出现。我们的理论计算支持了这一点。
