Sato Daisuke, Itatani Masaki, Matsui Jun, Unoura Kei, Nabika Hideki
Graduate School of Science and Engineering, Yamagata University, Japan.
Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata 990-8560, Japan.
Phys Chem Chem Phys. 2020 Oct 7;22(38):21672-21677. doi: 10.1039/d0cp03089a.
Periodic patterns are ubiquitous in nature and spontaneously form on molecular to cosmic scales by the interplay between reaction and diffusion. Understanding how these patterns form is important to understand the construction rules of nature and apply them in the synthesis of functional artificial materials. This work clarifies how radical (R˙) species affect pattern formation in periodic precipitated and depleted zones during a polymerization process in an agarose gel. When a monomer (Mon) solution was poured on top of the gel doped with an initiator (In) in a test tube, periodic and continuous precipitation occurred near and far away from the solution/gel interface, respectively. In contrast, a system without In exhibited only a continuous band of precipitates beyond a depleted zone without precipitates at a certain distance from the interface. In the depleted region, an inhibitor (Q) added to the solution limited the polymerization triggered by R˙ formed thermally from Mon. With the addition of enough In to overcome the quenching effect of Q, periodic bands appeared near the solution/gel interface. These results suggest the involvement of two independent polymerization processes: (i) polymerization triggered by R˙ formed from In, which is the dominant process up to 100 h and yields periodic structures near the interface. After 100 h, the dominant process is the polymerization triggered by R˙ generated thermally from Mon, which yields a continuous precipitation zone. These two R˙ species compete and generate periodic bands near the interface (<100 h) and a continuous band far away from the interface (>100 h).
周期性模式在自然界中无处不在，通过反应与扩散之间的相互作用，在从分子到宇宙的尺度上自发形成。理解这些模式如何形成对于理解自然的构建规则并将其应用于功能性人工材料的合成至关重要。这项工作阐明了自由基（R˙）物种如何在琼脂糖凝胶聚合过程中影响周期性沉淀和耗尽区中的模式形成。当将单体（Mon）溶液倒入装有引发剂（In）的试管凝胶顶部时，分别在溶液/凝胶界面附近和远处发生周期性和连续沉淀。相比之下，没有In的系统仅在距界面一定距离处没有沉淀的耗尽区之外表现出连续的沉淀带。在耗尽区域中，添加到溶液中的抑制剂（Q）限制了由Mon热形成的R˙引发的聚合反应。随着添加足够的In以克服Q的猝灭效应，在溶液/凝胶界面附近出现了周期性条带。这些结果表明涉及两个独立的聚合过程：（i）由In形成的R˙引发的聚合反应，这是长达100小时的主要过程，并在界面附近产生周期性结构。100小时后，主要过程是由Mon热产生的R˙引发的聚合反应，产生连续的沉淀区。这两种R˙物种相互竞争，在界面附近（<100小时）产生周期性条带，在远离界面处（>100小时）产生连续条带。
