Langmuir. 2018 Sep 18;34(37):11188-11194. doi: 10.1021/acs.langmuir.8b02335. Epub 2018 Sep 4.
Pattern formation based on the Liesegang phenomenon is considered one of the useful models for gaining a mechanistic understanding of spontaneous spatiotemporal pattern formations in nature. However, for more than a century, the Liesegang phenomenon in chemical systems has been investigated by using electrolytes as both the reaction substrate and aggregation promoter, which has obfuscated the role of the electrolyte. Here, we distinguish the electrolyte (NaSO) from the reaction substrates (Ag ion and citrate), where NaSO does not participate in the reaction step and acts as an aggregation promoter. The addition of NaSO in Ag-citrate-type Liesegang rings gave well-resolvable clear bands with a larger spacing coefficient. The observed changes were discussed by using the classical DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, where the role of the electrolyte is to shield the electrostatic repulsive interaction among the reaction products. Furthermore, the numerical simulation of the reaction-diffusion equation with different aggregation thresholds reproduced the salt-dependent change in the spacing coefficient. We expect that an understanding of the exact role of the electrolyte as the aggregation promoter reported here will offer novel insight into how nature spontaneously forms beautiful spatiotemporal patterns.
基于丽沙尔（Liesegang）现象的图案形成被认为是深入了解自然界中自发时空图案形成的机制的有用模型之一。然而，一个多世纪以来，化学体系中的丽沙尔现象一直是通过使用电解质作为反应底物和聚集促进剂来研究的，这掩盖了电解质的作用。在这里，我们将电解质（NaSO）与反应底物（Ag 离子和柠檬酸盐）区分开来，其中 NaSO 不参与反应步骤，而是作为聚集促进剂。在 Ag-柠檬酸盐型丽沙尔环中添加 NaSO 会给出分辨率更好的清晰带，且带间距系数更大。使用经典的 DLVO（德加古林-兰德维格-奥弗贝克）理论讨论了观察到的变化，其中电解质的作用是屏蔽反应产物之间的静电排斥相互作用。此外，使用不同聚集阈值的反应-扩散方程的数值模拟再现了盐依赖性的间距系数变化。我们期望，这里报道的电解质作为聚集促进剂的确切作用的理解将为了解自然界如何自发形成美丽的时空图案提供新的见解。
