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Crystal structures of bubbles
08 February 2006
Researchers have used household detergent to create, for the first time, arrays of bubbles that mirror the atomic arrays found in crystals.
Stefan Hutzler and colleagues at Trinity College, Dublin, Ireland, have observed periodic arrays of bubbles in wet foams. The three-dimensional ordered structures were made of bubbles around 200 micrometres in diameter formed by introducing nitrogen through a nozzle into a solution containing ordinary washing-up liquid. The structures were one million times bigger than atomic arrays found in crystals and at least five layers thick.
Hutzler estimated that, with the size of bubbles they have, foams of up to 25 layers can be made. His team saw defects in the structures like those in solid-state crystals, such as vacancies, stacking faults and surface terraces. Of 48 samples studied, the group found that, instead of face-centred cubic packing and hexagonal close packing occurring equally, the former outweighed the latter by roughly three to two.
Hutzler's team plan to look into these foams using methods such as cryomicroscopy and synchrotron tomography. However, for Hutzler, the key question remains: when there is so much order in this macroscopic system, why do particles of comparable size not display this kind of order?
Neil D Withers
A van der Net, W Drenckhan, D Weaire and S Hutzler, Soft Matter, 2006, 2, 129 (DOI: 10.1039/b515537a)