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Five-dimensional imaging of freezing emulsions with solute effects

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Science  20 Apr 2018:
Vol. 360, Issue 6386, pp. 303-306
DOI: 10.1126/science.aar4503

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Images frozen in time

Freezing processes involving multiple phases are common, as seen in the zone refining used to remove impurities from a crystal through the heating of a narrow region. However, it is difficult to visualize the processes as they happen. Dedovets et al. studied the freezing of an oil-in-water emulsion and the interaction of the oil droplets with the leading edge of the freezing water. In situ visualization of the freezing front was achieved through confocal microscopy of samples on a moving sample holder. The authors tracked the effects of solution concentration on the droplet positions and observed premelting at the interface of the droplets by using fluorescence markers.

Science, this issue p. 303

Abstract

The interaction of objects with a moving solidification front is a common feature of many industrial and natural processes such as metal processing, the growth of single crystals, the cryopreservation of cells, or the formation of sea ice. Interaction of solidification fronts with objects leads to different outcomes, from total rejection of the objects to their complete engulfment. We imaged the freezing of emulsions in five dimensions (space, time, and solute concentration) with confocal microscopy. We showed that the solute induces long-range interactions that determine the solidification microstructure. The local increase of solute concentration enhances premelting, which controls the engulfment of droplets by the front and the evolution of grain boundaries. Freezing emulsions may be a good analog of many solidification systems where objects interact with a solidification interface.

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