Effect of Competitive Complex Formation on Patterning and Front Propagation in Periodic Precipitation

Shreif, Zeina; Al-Ghoul, Mazen; Sultan, Rabih

doi:10.1002/1439-7641(20020715)3:7<592::aid-cphc592>3.0.co;2-z

Cited by 11 publications

(14 citation statements)

References 13 publications

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“…2,3,16,17 The introduction of a foreign cation that competes with Co 2+ for both precipitation and complex formation could interfere with the processes involved and is thus expected to significantly alter the dynamics of the Co(OH) 2 system. 1 The dominance of complex formation with ammonia for the foreign ion suppresses the dissolution of cobalt hydroxide. Ni 2+ is one such suitable foreign ion, because the solubility product constant of Ni(OH) 2 is similar to that of Co(OH) 2 , while the formation constant for the Ni(NH 3 ) 6 2+ complex is a few orders of magnitude higher than that of Co(NH 3 ) 6 2+ .…”

Section: Introductionmentioning

confidence: 99%

Front Propagation in Patterned Precipitation. 3. Composition Variations in Two-Precipitate Stratum Dynamics

et al. 2007

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This paper is a study of the composition dynamics of Liesegang band strata of Co(OH)2 and Ni(OH)2 from NH4OH, with redissolution by complex formation with ammonia. At a fixed time, the cobalt hydroxide composition was found to exhibit a random variation with band number, yet within a general overall decrease. The decrease with band number becomes more pronounced as the initial concentrations of Co2+ and Ni2+ get closer to each other. At equal concentrations, periodic oscillations in Co(OH)2 composition appear over consecutive bands. The time evolution of the total Co(OH)2 mass percent (over the entire pattern of strata) passes through a maximum. The dynamics of this complex system has been simulated by theoretical calculations using the model of Müller and Polezhaev, modified by Al-Ghoul and Sultan in a series of two papers in J. Phys. Chem. A; the present paper is the third in the series. The simulations capture the essential features of the experimentally observed dynamics.

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Section: Introductionmentioning

confidence: 99%

Front Propagation in Patterned Precipitation. 3. Composition Variations in Two-Precipitate Stratum Dynamics

et al. 2007

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“…In a series of papers, [1][2][3][4][5][6][7] we studied a variety of features of patterned precipitation (Liesegang banding 8,9 ) while focusing on a specific system: Co(OH) 2 precipitated from NH 4 OH diffusing into a gel medium of Co 2þ . This Liesegang system differs from the other classical patterns, in that it has interesting dynamical properties emerging from the propagation of the whole stratum of bands with the diffusion front.…”

Section: Introduction 11 Backgroundmentioning

confidence: 99%

Taming ring morphology in 2D Co(OH)2 Liesegang patterns

Shreif

Mandalian

Abi-Haydar

et al. 2004

Phys. Chem. Chem. Phys.

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We present here novel expermients on the formation of Liesegang rings in 2D. We consider the system of propagating Co(OH) 2 bands studied extensively in 1D, from the viewpoint of a large number of considerations. In this paper, we focus on morphological aspects and, in the first part, we seek to steer the appearance of the pattern to achieve a pre-determined morphology. We aim at attaining three main features: minimizing the re-dissolution of Co(OH) 2 at the back of the propagating pattern, clearing the fuzzy precipitate region lagging behind, and increasing the ring spacing. We vary three experimental parameters to achieve that threefold purpose: 1. decreasing the concentration of the diffusing (outer) electrolyte (NH 4 OH), 2. applying a constant electric field radially across the circular pattern, and, 3. increasing the gel concentration to a moderately high value. The best pattern was obtained under the conditions: 9% gelatin, [NH 4 OH] 0 ¼ 1.33 M, and applied potential V ¼ 4.0 V, for a 0.100 M CoCl 2 taken as constant throughout the whole set of experiments performed. The observations are discussed in relation to the effects that cause them, and the known properties of Liesegang patterns. In the second part of the study, we monitor distortions of the ring pattern from circular symmetry, by applying a constant linear electric field across the circular medium. Elliptical distortions are obtained, which become notably important as the applied potential increases through 1.75 V. The variation of the ring curvature with applied potential is quantified and discussed.

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“…Of particular interest and richness in the pattern display, are systems where multiple co-precipitate ions of one kind (cations or anions) are involved in the dynamics. Two-precipitate Liesegang systems have been studied [32,33], and sometimes classified [34]. The onset of real complex rhythmicity starts with three-component systems.…”

Section: Complex Liesegang Patternsmentioning

confidence: 99%

Rhythmic precipitate patterns and fractal structure

Sultan

2011

Acta Mech Sin

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Liesegang patterns of parallel precipitate bands are obtained when solutions containing co-precipitate ions interdiffuse in a 1D gel matrix. The sparingly soluble salt formed, displays a beautiful stratification of discs of precipitate perpendicular to the 1D tube axis. The Liesegang structures are analyzed from the viewpoint of their fractal nature. Geometric Liesegang patterns are constructed in conformity with the well-known empirical laws such as the time, band spacing and band width laws. The dependence of the band spacing on the initial concentrations of diffusing (outer) and immobile (inner) electrolytes (A 0 and B 0 , respectively) is taken to follow the Matalon-Packter law. Both mathematical fractal dimensions and box-count dimensions are calculated. The fractal dimension is found to increase with increasing A 0 and decreasing B 0 . We also analyze mosaic patterns with random distribution of crystallites, grown under different conditions than the classical Liesegang gel method, and report on their fractal properties. Finally, complex Liesegang patterns wherein the bands are grouped in multiplets are studied, and it is shown that the fractal nature increases with the multiplicity.

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Effect of Competitive Complex Formation on Patterning and Front Propagation in Periodic Precipitation

Cited by 11 publications

References 13 publications

Front Propagation in Patterned Precipitation. 3. Composition Variations in Two-Precipitate Stratum Dynamics

Front Propagation in Patterned Precipitation. 3. Composition Variations in Two-Precipitate Stratum Dynamics

Taming ring morphology in 2D Co(OH)2 Liesegang patterns

Rhythmic precipitate patterns and fractal structure

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