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

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, tuning of the time scale of diffusional spreading of hydroxide ions with respect to that of the phase separation drives the mode selection between one-dimensional band and two-dimensional spot patterns.