Materials Science

The (S)lowdown on Crystallization

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Science  08 Apr 2011:
Vol. 332, Issue 6026, pp. 151
DOI: 10.1126/science.332.6026.151-b

One way to resolve the many steps that occur during crystallization is to use small droplets of solution, in part to avoid heterogeneous nucleation by impurities. Stephens et al. created picoliter droplets by using self-assembled monolayers (SAMs) that contained hydrophilic (carboxylic acid terminated) islands inside hydrophobic (fluorous terminated) layers. These islands supported hemispherical droplets, with radii varying from 4 to 10 µm (0.04 to 2 pl in volume), that were supersaturated with calcium carbonate. Bulk precipitation created many rhombohedral crystals, but in 90% of the droplets, a single smaller tetrahedral crystal formed. Redissolution of these tetrahedral crystals in undersaturated solution, or further growth from bulk solution, initiated recrystallization into rhombohedral crystals. The SAMs appear to slow down crystallization and capture the tetrahedron as an early intermediate crystal form.

J. Am. Chem. Soc. 133, 10.1021/ja200309m (2011).

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