Irregular Liesegang-type patterns in gas phase revisited. I. Experimental setup, data processing, and test of the spacing law

Abstract

Since the early work on Liesegang rings in gels, they have been a reference point for the study of pattern formation in chemical physics. Here we present a variant of the Liesegang experiment in gas phase, where ammonia and hydrochloric acid react within a glass tube producing a precipitate, which deposits along the tube wall producing a spatial pattern. With this apparently simple experiment a wide range of rich phenomenon can be observed due to the presence of convective flows and irregular dynamics reminiscent of turbulent behavior, for which precise measurements are scarce. In this first part of our work, we describe in detail the experimental setup, the method of data acquisition, the image processing, and the procedure used to obtain an intensity profile, which is representative of the amount of precipitate deposited at the tube walls. Special attention is devoted to the techniques rendering a data series reliable for statistical studies and model building, which may contribute to a characterization and understanding of the pattern formation phenomenon under consideration. As a first step in this direction, based on our data, we are able to show that the observed band pattern follows, with slight deviations, the spacing law encountered in common Liesegang rings, despite that the experimental conditions are very different. A further statistical correlation analysis of the data constitutes Paper II of this research.

Band Propagation, Scaling Laws, and Phase Transition in a Precipitate System III: Effect of the Anions of Precursors

“…While the chloride system (Figure B) also exhibits Liesegang bands, however, the spacing between consecutive bands is irregular yet reproducible. Irregular Liesegang banding rarely occurs; however, it was reported in a gel medium and in the gas phase. , The bromide system (Figure C) exhibits Liesegang banding with reverse spacing in an opposite trend to the nitrate system. The sulfate system (Figure D) forms a propagating pulse followed by a hazy zone in which Liesegang banding might later be witnessed. , Clearly, the four systems exhibit four different Liesegang patterns, which will be characterized microscopically and macroscopically in the following sections.…”

“…Irregular Liesegang banding rarely occurs; however, it was reported in a gel medium 21 and in the gas phase. 22,23 The bromide system (Figure 1C) exhibits Liesegang banding with reverse spacing 24 in an opposite trend to the nitrate system. The sulfate system (Figure 1D) forms a propagating pulse followed by a hazy zone in which Liesegang banding might later be witnessed.…”