Editor's Summary

3 July 2008

Emulsions and pastes: The importance of being thin

The spreading of a paste or emulsion on a surface is a familiar everyday process — for example, the application of skin cream. Yet the underlying physics is complex. If too 'liquid' or too 'solid', the cream will not do the job. The properties of these materials lie somewhere between those of solids and liquids, and the relationship between the stresses and strains in the resulting flows are not trivial. Now Goyon et al. show that these thin films exhibit behaviour very different from that of the material in its bulk form, because of the influence of film thickness and the roughness of the surface on which they are flowing. For example, a thin creamy film may spread much more easily than predicted from its bulk flow properties. Such behaviour should be relevant in contexts ranging from the industrial processing of food and cosmetics to the geophysical hazards associated with debris flows.

Letter: Spatial cooperativity in soft glassy flows

J. Goyon, A. Colin, G. Ovarlez, A. Ajdari & L. Bocquet

doi:10.1038/nature07026

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