Abstract
Liesegang pattern formations are widely spread in nature. In spite of a comparably simple experimental setup under laboratory conditions, a variety of spatio-temporal structures may arise. Presumably because of easier control of the experimental conditions, Liesegang pattern formation was mainly studied in gel systems during more than a century. Here we consider pattern formation in a gas phase, where beautiful but highly complex reaction-diffusion-convection dynamics are uncovered by means of a specific laser technique. A quantitative analysis reveals that two different, apparently independent processes, both highly correlated and synchronized across the extension of the reaction cloud, act on different time scales. Each of them imprints a different structure of salt precipitation at the tube walls.
Highlights
Liesegang rings are a special type of chemical pattern formation that involves reaction- diffusion processes leading to precipitates that are not uniformly but rhythmically distributed[1,2,3]
The authors concluded that the Liesegang ring formation requires supersaturation of the individual gases, as in nucleation phenomena, and a critical cluster size necessary for the crystal growth to take place
We study the dynamics of the vapour-to-particle HCl/NH3 system using the experimental configuration for diffusing gases in the glass tube[14]
Summary
Liesegang rings are a special type of chemical pattern formation that involves reaction- diffusion processes leading to precipitates that are not uniformly but rhythmically distributed[1,2,3]. Several theories that include diffusion, reaction, nucleation, and crystal growth have been proposed to explain the Liesegang ring formation[5,6,7,8]. An interesting but less studied case of Liesegang-type ring formation is the vapour-to-particle HCl/NH3 reaction system first reported in 195114 In this particular experiment reactants are placed initially at opposite ends of an air-filled glass tube and diffuse in order to yield solid NH4Cl. In this particular experiment reactants are placed initially at opposite ends of an air-filled glass tube and diffuse in order to yield solid NH4Cl For this case, the authors concluded that the Liesegang ring formation requires supersaturation of the individual gases, as in nucleation phenomena, and a critical cluster size necessary for the crystal growth to take place. In their work no further quantitative analysis was performed
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