Pierre-Gilles de Gennes Quotes
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The essential property of insoluble bilayers is that they optimise their area at fixed surfactant number.
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Surfactants allow us to protect a water surface and to generate these beautiful soap bubbles, which are the delight of our children.
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Usually a fiber, after being dipped in a liquid, shows a string of droplets, and thus, for some time, people thought that most common fibers were non-wettable.
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The final lines are not mine: they come from an experiment on soft matter, after Boudin… An English translation might run like this:
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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.
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What do we mean by soft matter? Americans prefer to call it 'complex fluids.' This is a rather ugly name, which tends to discourage the young students.
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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.
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I have emphasized experiments more than theory. Of course, we need some theory when thinking of soft matter.