Macroscopic Pattern Formation of Alginate Gels in a Two-Dimensional System

Macroscopic spatial patterns were formed in calcium alginate gels when a drop of a calcium nitrate solution was placed on the center of a sodium alginate solution on a petri dish. These patterns have been classified into two groups. One is multi-concentric rings consisting of alternating cloudy and transparent areas observed around the center of petri dishes. The other is streaks extending to the edge of the petri dish, which are formed to surround the concentric bands between the concentric bands and the petri dish edge. We have attempted to understand the origins of the pattern formations using the properties of phase separation and gelation. The distance between two adjacent concentric rings was roughly proportional to the distance from where the calcium nitrate solution was dropped. The proportional factor p increased exponentially for the inverse of the absolute temperature of the preparation. The p also depended on the concentration of alginate. The pattern characteristics in the concentric pattern agreed with those in the Liesegang pattern. The paths of radial streaks were disturbed at high temperatures. The length of these streaks shortened with increasing alginate concentration. The characteristics of the streaks were similar to those of crack patterns resulting from inhomogeneous shrinkage during drying.

Automated summary

Macroscopic spatial patterns formed in calcium alginate gels consist of multi-concentric rings and streaks. The distance between concentric rings is proportional to the distance from which the calcium nitrate solution was dropped, and this proportionality factor depends on the temperature and alginate concentration. The patterns in the concentric rings are similar to Liesegang patterns, while the streaks resemble crack patterns resulting from inhomogeneous shrinkage during drying.