Effect of the Polarity of Solvents on Periodic Precipitation: Formation of Hierarchical Revert Liesegang Patterns

Abstract

Liesegang pattern (LP) is one example of self-organized periodic precipitation patterns in nonequilibrium systems. Several studies have demonstrated that the LP morphology can track physicochemical environmental conditions (e.g., temperature); however, the polarity effect has not been explored to date. In this study, a copper chromate system is used to reveal the impact of solvent polarity on the evolving LP structure using water/organic solvent mixtures. In the typical case of using water/dimethyl sulfoxide (DMSO) mixtures, two drastic changes in LP morphology with increasing DMSO contents were found: (i) increasing frequency of the original structure and (ii) formation of a hierarchical pattern with the appearance of another, lower-frequency structure. Furthermore, the simulation model operating with a bimodal size distribution, allowing both homogeneous and heterogeneous precipitations showed good agreement with the experimental results. Therefore, this study demonstrated that LP can be tailored by solvent polarity and can be used for designing hierarchical precipitation patterns in a straightforward manner.

Non‐equilibrium‐Growing Aesthetic Ionic Skin for Fingertip‐Like Strain‐Undisturbed Tactile Sensation and Texture Recognition

“…This suggests that the reaction-diffusion process was continuously disturbed by another process, in this case, the polymerizing process which in turn affected the diffusion of reagents and precipitation threshold. [41,42] We further demonstrate that the same as the mirrored papillary and intermediate ridges in fingertips, Liesegang patterns are present throughout the hydrogel, as evidenced by the cross-sectional photograph (Figure 2e). The heights of the ridges increase with band numbers with values of 210-340 µm (Figure 2f), which is much higher than that of human fingerprint papillary ridges (59.0 ± 19.2 µm).…”

“…This suggests that the reaction‐diffusion process was continuously disturbed by another process, in this case, the polymerizing process which in turn affected the diffusion of reagents and precipitation threshold. [ 41,42 ]…”

“…Because Liesegang patterning occurs far from thermodynamic equilibrium, the spacing, widths, and heights of Liesegang bands are influenced by many factors, including temperature, electrolyte concentration, pH, gel crosslinking degree, additive, and solvent polarity. [39,41,42,44,45] Here, we adjusted the concentration of the inner electrolyte (K 2 CrO 4 ) to control the patterning density. As shown in Figures S4 and S5 Information), lowering the concentration of K 2 CrO 4 (0.01 and 0.015 m) to reduce the reaction rate would generate lower patterning densities with larger spacing and band widths, while the heights of ridges were also reduced.…”

Synthesis of Zeolitic Imidazolate Framework-8 Using Glycerol Carbonate

“…Moreover, the use of GlyC fully respects the 7th principle of Green Chemistry − due to its preparation from glycerol through transcarbonation with dimethyl carbonate. Because of its physicochemical properties (Table S1 in Supporting Information), GlyC is also used as a biodegradable, low-volatile organic solvent with low toxicity having a high dielectric constant and dipole moment . Indeed, GlyC shows relevant and promising properties to overcome the limitations related to DMF for ZIF-8 preparation.…”

Complex Patterning of Matter with Liesegang Patterns Propagating through Different Concentration Media─Gel Lenses for Liesegang Waves

“…Mathematically well-defined LP forming systems are ideal platforms for testing the effect of various external factors such as concentration of reagents, temperature, , mechanical deformation, electrical and magnetic fields, − impurities in the gel, pH of the media, , light, solvent and polarity effects, ionic strength, and gravity on the reaction-diffusion systems. Different environmental conditions lead to different band distances and widths, revert-spaced LPs, bands with secondary structures, spirals, fractals, and 3D helices .…”