User:Brian P. Josey/Notebook/2010/02/05
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Looking Through the Scope
We tried some 3 micron magnetic beads in the microscope today. When you look at them through the microscope, they are reddish-brown in color, and are little circles. We found that through the scope, you can get them move towards a magnet, where the clump together in a large group, but are still a little repulsive to each other. This is because they have their magnetic domains lined up in the same direction, but this effect was not profound.
When the water began to dry, it left behind structures of beads that looked interesting. Koch called it "coffee-ring physics." They did resemble coffee rings left on a table. As the water was drying out, you could track the meniscus line across the slide, because a line of beads developed that outlined the boundary between the wet and dry spots. The wet spots would have beads spread out randomly, while the dry spot was dark, and had the "coffee-ring" structures.
Beads in a tube
I was also playing with a sample of magnetic beads in a clear tube. After they had been sitting in the refrigerator for a long time, all of the beads settled to the bottom of the tube. When I mixed the tube up, the beads returned to solution, and made the previously clear liquid brown in color. A magnet would move the beads around inside the tube, and given enough time, a magnet next to the tube would change the brown solution to clear, with the metallic beads clumped as close to the magnet as possible.