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Fancy foams from common surfactant

Foams formed by the dispersion of gas bubbles in a fluid are interesting materials. They are well organized over several length-scales, starting at the molecules at the gas-liquid interfaces to the bubbles in the foam. This gives foam its properties (mechanical, acoustic, etc) that make it such an attractive material and foams with novel functionalities are continuously developed for both industrial processes and household products. Foams are used in applications ranging from medical imagery, to ceramics, oil extraction, and decontamination processes.

Despite the possibilities offered by foams, it is not easy to make foams that are stable for long periods of time. A team of researchers at the LPS (Laboratoire de Physique des Solides) of Université Paris-Sud has shown that it is possible to make ultrastable foams that can be destroyed on demand by simple heating.

Ultrastable foams are made very simply by adding salt (NaCl or KCl) to sodium dodecyl sulfate. The addition of high concentrations of salt leads to the precipitation of the surfactant on the bubble surfaces and as crystals in the interstices between the bubbles. As a consequence, the ageing of the foams is stopped to make them stable indefinitely, or until they are heated above the melting temperature of the crystals. The use of KCl is shown to be much more effective than that of NaCl because potassium dodecyl sulfate has a higher melting temperature and faster rates of crystallization. The crystalline structures have been investigated inside the foam using small angle neutron scattering in collaboration with colleagues from Laboratoire Léon Brillouin and ECE Paris.
These foams could see many uses in the near future due to their elegant simplicity, which makes for affordable foams that can be both ultrastable and thermostimulable.

Reference :
L. Zhang, A. Mikhailovskaia, P. Yazhgur, F. Muller, F. Cousin, D. Langevin, N. Wang, A. Salonen,
Precipitating Sodium Dodecyl Sulfate to Create Ultrastable and Stimulable Foams
Angewandte Chemie 55, 9533-9536 (2015).

Contact : Anniina Salonen