posted on 2024-02-21, 03:30authored byElee A. Siev, Bruno C. Batista, Oliver Steinbock
Chemical gardens are self-organized
precipitate structures
such
as thin-walled tubes and membrane-bound cells reminiscent of biological
shapes. These usually inorganic precipitates compartmentalize the
reaction system and allow the study of materials synthesis in very
steep concentration gradients. We create such tubes by steadily injecting
a mixture of MnCl2 and CuSO4 solutions into
a large reservoir of sodium silicate solution. The growing tube is
open at its tip and ejects a stream of colloidal particles that aggregate
to form a secondary tube above the original one. This secondary tube
can coil into a tightly wound nest-like structure, freely suspended
underneath the solution–air interface. Using three-dimensional
image reconstruction, we analyze the onset of coiling and show that
the structure is helical with a helix radius that increases in the
vertical direction. The height at which the coiling begins is lowered
with each successive repeat of the growth experiment, suggesting that
coiling is induced by small variations in the density of the silicate
solution.