Pattern Formation in Precipitation Reactions: The Liesegang Phenomenon.

Hideki Nabika,István Lagzi,Masaki Itatani

doi:10.1021/acs.langmuir.9b03018

Abstract

Pattern formation is a frequent phenomenon in physics, chemistry, biology, and materials science. Bottom-up pattern formation usually occurs in the interaction of the transport phenomena of chemical species with their chemical reaction. The oldest pattern formation is the Liesegang phenomenon (or periodic precipitation), which was discovered and described in 1896 by Raphael Edward Liesegang, who was a German chemist and photographer who was born 150 years ago. The purpose of this feature article is to provide a comprehensive overview of this type of pattern formation. Liesegang banding occurs because of the coupling of the diffusion process of the reagents with their chemical reactions in solid hydrogels. We will discuss several phenomena observed and discovered in the past century, including reverse patterns, precipitation patterns with dissolution (due to complex formation), helicoidal patterns, and precipitation waves. Additionally, we will review all existing models of the Liesegang phenomenon including pre- and postnucleation scenarios. Finally, we will highlight several applications of periodic precipitation.

Highlights

Self-assembly and self-organization are frequent phenomena in nature, and they are used to design either complex equilibrium or nonequilibrium spatiotemporal structures and patterns at the nano, micro, and macroscale.[1]
Pattern formation is the appearance of the nonhomogeneous spatial distribution of the concentration of one or more chemical species
Reactiondiffusion patterns are one of the categories of the patterns, in which pattern formation is governed by the diffusion and reaction of the chemical species

Summary

■ INTRODUCTION

Self-assembly and self-organization are frequent phenomena in nature, and they are used to design either complex equilibrium or nonequilibrium spatiotemporal structures and patterns at the nano-, micro-, and macroscale.[1]. Well-known and studied examples of reaction-diffusion systems are Turing pattern formation[2] and wave propagation in excitable media (via the Belousov−Zhabotinsky, BZ, reaction).[3] These patterns are nonequilibrium structures, and to generate Turing patterns, continuous stirred tank reactors (CSTRs) are employed to maintain the chemical system far from its thermodynamic equilibrium.[4] A special class of reaction-diffusion systems is the precipitation pattern (including the Liesegang phenomenon) in which the reaction is represented by a precipitation reaction yielding precipitate and/or colloidal particles, resulting in a heterogeneous chemical system. Initially one of the reagents is homogeneously distributed in a gel (called the inner electrolyte, B), and after the gelation process, the solution of the other reagents (called the outer electrolyte, A) is placed on Received: September 25, 2019 Revised: November 17, 2019 Published: November 27, 2019

Invited Feature Article

■ ACKNOWLEDGMENTS

Findings

■ REFERENCES