Unveiling the Wonders of Chemical Gardens: Chemistry’s Adaptive Marvels

Credit: Courtesy of Florida State University

Researchers from Florida State University have unveiled a mathematical model that sheds light on the growth, pattern formation, and self-healing properties of chemical gardens. This breakthrough could pave the way for the development of innovative self-repairing materials.

Chemists have been captivated by the vibrant, coral-like structures that emerge from the mixing of metal salts in small bottles since the mid-1600s. Until now, the intricate workings, patterns, and underlying principles governing the formation of these seemingly straightforward tubular structures, known as chemical gardens, have remained elusive.

In a recent publication in the Proceedings of the National Academy of Sciences, scientists from Florida State University present a comprehensive model that elucidates how these structures ascend, adopt various shapes, and transition from pliable, self-healing substances to more brittle ones.

FSU Professor of Chemistry and Biochemistry, Oliver Steinbock, remarked on the significance of these findings in a materials context, stating, “They don’t grow like crystals. A crystal possesses well-defined edges and develops layer by layer through atomic deposition. In a chemical garden, however, when a breach occurs, it undergoes self-healing. These preliminary findings represent a crucial stride towards creating materials capable of reconfiguring and mending themselves.”

Typically, chemical gardens form when metal salt particles interact with a silicate solution. The dissolving salt reacts with the solution, giving rise to a semi-permeable membrane that protrudes upwards in the liquid, resembling a biological structure akin to coral.

Chemical gardens were initially observed in 1646, and their captivating formations have intrigued scientists for centuries. The chemistry underlying their creation is connected to the emergence of hydrothermal vents and the corrosion of steel surfaces, where insoluble tubes can manifest.

Steinbock explained, “These were recognized as peculiar entities. They have a rich history in the field of chemistry. While they had become more of a demonstration experiment, scientists have rekindled their interest in them over the past two decades.”

The inspiration for the mathematical model developed by Steinbock, along with postdoctoral researcher Bruno Batista and graduate student Amari Morris, stemmed from experiments involving the gradual injection of a salt solution into a larger volume of silicate solution confined between two horizontal plates. These experiments revealed distinctive growth modes and showcased how the material begins as stretchy but progressively becomes stiffer, eventually succumbing to fracture.

The confinement within the two layers enabled the researchers to simulate various shape patterns, ranging from floral motifs to hair-like strands, spirals, and even worms.

In their model, the researchers delineated the emergence of these patterns throughout the chemical garden’s development. Although salt solutions can differ significantly in their chemical compositions, the model successfully explained the universality of pattern formation.

For instance, the patterns may involve loosely arranged particles, folded membranes, or self-extending filaments. Moreover, the model corroborated the observation that fresh membranes expand in response to minute breaches, demonstrating the material’s remarkable self-healing capabilities.

Batista expressed his satisfaction with the model, stating, “The essence of the shape and growth of chemical gardens has been captured in our work.”

Reference: “Pattern selection by material aging: Modeling chemical gardens in two and three dimensions” by Bruno C. Batista, Amari Z. Morris, and Oliver Steinbock, 3 July 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2305172120

This research received support from NASA and the National Science Foundation.

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• Proceedings of the National Academy of Sciences: Pattern selection by material aging: Modeling chemical gardens in two and three dimensions
• Florida State University: Chemistry’s Chameleon: The Self-Repairing Marvels of Chemical Gardens