Fine tuning of pattern selection in the cadmium–hydroxide-system

Abstract

Controlling self-organization in precipitation reactions has received growing attention in the efforts of engineering highly ordered spatial structures. Experiments have been successful in regulating the band patterns of the Liesegang phenomenon on various scales. Herein we show that by adjusting the composition of the hydrogel medium we can switch the final pattern between the classical band structure and the rare precipitate spots with hexagonal symmetry. The accompanying modeling study reveals that besides the modification of gel property, the tuning of the time scale of diffusional spreading of hydroxide ion with respect to that of the phase separation drives the mode selection between one-dimensional band and two-dimensional spot patterns.

Modification of the Matalon–Packter Law for Self-Organized Periodic Precipitation Patterns by Incorporating Time-Dependent Diffusion Flux

“…As mentioned above, F diff is proven to be the key factor determining the periodicity of LPs. − Furthermore, it was recently reported that the F diff of OH – as the outer electrolyte could trigger a transition in the formed pattern morphology between band (ring) and spot structures when researchers controlled F diff using a polymer hydrogel with carboxylic acid residues as the reaction medium . What is common among the abovementioned studies is that F diff is strongly involved in the LP formation mechanism, regardless of the intrinsic or extrinsic control techniques used in the systems.…”

“…32−34 Furthermore, it was recently reported that the F diff of OH − as the outer electrolyte could trigger a transition in the formed pattern morphology between band (ring) and spot structures when researchers controlled F diff using a polymer hydrogel with carboxylic acid residues as the reaction medium. 57 What is common among the abovementioned studies is that F diff is strongly involved in the LP formation mechanism, regardless of the intrinsic or extrinsic control techniques used in the systems. However, as one of the most important theories of LP formation, the MP law does not take into account changes in F diff caused by factors other than the initial concentrations of the outer and inner electrolytes, especially the reservoir volume.…”