Evolution of Liesegang patterns through gel concentration borders and thermal changes

Baytekin, Bilge
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Bilkent University
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Liesegang Patterns (LPs) are under the umbrella of periodic precipitation patterns that are formed through reaction- diffusion (RD). Liesegang Patterns can be used to track down the changes in the physical environment, because different physical environments produce different environments. Since their discovery effects of various parameters such as temperature, magnetic ,and electric fields, concentrations of electrolytes and gels have been studied to understand the formation mechanisms of these patterns. In this study an LP system (CuSO4 (outer electrolyte)/ K2CrO4 (inner electrolyte) in agarose hydrogel) that responds to changes in the gel environments was generated. The medium uniformity with different gel concentration regions designed in various geometries (circle, square, triangle, and pentagon) were used to break the symmetry ,and homogeneity in the medium. The propagation of LP waves across the boundaries between the regions was visually inspected. The LP band spacings, the size ,and morphology of the product within the bands were altered in comparison to those observed in with LPs in homogenous media. The first part of the work is the first display of LP waves travelling through concentration boundaries. The visual patterns obtained in spatially heterogeneous media provide complex patterning of matter, which is not only fundamentally interesting for the study of artificial patterning but also can be useful in fields such as catalysis, and soft functional materials.
Second, the propagation of the “bio” waves of bacteria colony Bacillus Subtilis growth through different concentration gel media was monitored. Different concentrations of agar ,and tryptone across a boundary in the growing medium led to changes in the growth patterns of bacteria upon passing to the “other side”. These changes growing bacterial patterns can be used to analyse how the spatial changes in the environment affect the growing colonies ,and give a more realistic view on the bacterial growth on complex terrain. Finally, we explore the effect of temperature ,and the hydrogel chemistry (gelatin, agarose, and PVA) on the formation of Mg(OH)2 LPs. Previously, temperature was used only to change the LP spacings and particle size. This work shows that it can also be used to alter the morphology of the formed particles. The results of this part of the project imply that a temperature gradient can be used to produce patterns with diverse morphologies of the same species in the same spatial environment.
All these parts in the thesis work point out that simple symmetry breaking in the medium can make significant changes in the ‘developing’ systems in the macro, and micro scales. This information can be used in analysis ,and utilization of natural ,and synthetic patterns systems.

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Liesegang patterns, Periodic precipitation, Agarose hydrogel, Particle growth
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