Chemistry

Synthesizing Siliceous Spiny Shells

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Science  10 Jan 2003:
Vol. 299, Issue 5604, pp. 167
DOI: 10.1126/science.299.5604.167c

Unicellular organisms such as diatoms and radiolaria make intricately patterned shells or tests, consisting mainly of amorphous silica. It has been suggested that these structures form through repeated phase separation events at decreasing length scales. To study this process, Volkmer et al. have developed a simple biomimetic model system.

A surfactant-stabilized oil droplet is microinjected into an aqueous solution. Organic additives in the oil droplet induce spontaneous emulsification: the surface of the droplet develops protruding spines, which grow and then separate from the original droplet to form smaller droplets until the parent droplet disappears. When the oil droplet also contains a metal (silicon or titanium) oxide precursor that can hydrolyze at the oil-water interface, a mineralized shell results. The concentration of the metal oxide precursor can be varied so that the spines are preserved. The star-shaped morphology bears some resemblance to that of the radiolaria, which have silica shells with fine radial spines. — JFU

Angew. Chem. Int. Ed. 42, 58 (2003).

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