When I pour dry lentils into a water bowl, I notice many of them form little clusters, with an air bubble in the center.
Why does this happen? I'm guessing something about static electricity. But not sure bubbles or lentils have charge...
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when a dry lentil first encounters water, the water initially does not wet the surface of the lentil well- that is, the lentil is happier in contact with air rather than with water. This means if there's an air bubble adjacent to a lentil in water, the lentil segregates itself by sticking to the bubble- and hence, the lentils will cluster themselves around that bubble.
Now if you leave lentils in contact with water long enough, eventually the lentil surface will begin to absorb water and then, when the water in the vicinity "looks" at that lentil, it "sees" not the lentil skin but instead a layer of water molecules that have soaked into the skin, which looks just like more water. The lentil then lets go of the bubble and the lentil becomes completely wet.
The dynamics of this process are well-described by something called interfacial surface energy. Try a search on that for more details.
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