Wednesday, June 19, 2019 Text is available under the CC BY-SA 3.0 licence.

Pierre-Gilles de Gennes (1932 – 2007)

French physicist and the Nobel Prize laureate in Physics in 1991.
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Pierre-Gilles de Gennes
A dense film of a conventional surfactant is quite impermeable. On the other hand, a dense film of Janus grains always has some interstices between the grains, and allows for chemical exchange between the two sides; "the skin can breathe". This may possibly be of some practical interest.
Gennes quotes
Benjamin Franklin performed a beautiful experiment using surfactants; on a pond at Clapham Common, he poured a small amount of oleic acid, a natural surfactant which tends to form a dense film at the water-air interface. He measured the volume required to cover all the pond. Knowing the area, he then knew the height of the film, something like three nanometers in our current units. This was to my knowledge the first measurement of the size of molecules. In our days, when we are spoilt with exceedingly complex toys, such as nuclear reactors or synchrotron sources, I particularly like to describe experiments of this Franklin style to my students.
Surfactants allow us to protect a water surface, and to generate these beautiful soap bubbles, which are the delight of our children.
Le vrai point d'honneur [d'un scientifique] n'est pas d'?tre toujours dans le vrai. Il est d'oser, de proposer des idées neuves, et ensuite de les vérifier.

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