Hey everyone! For this Macademics post I decided to talk about this cool thing called the Leidenfrost Effect.
This is a phenomenon that causes water droplets to float and roll off of hot surfaces. You may have noticed this while you were cooking or if you've ever poured liquid nitrogen on the floor that the droplets skid across a hot surface. It's pretty cool with liquid nitrogen so if you're in a lab that has left over liquid nitrogen from an experiment, dump it on the floor and see what happens, or find a YouTube video - either way works.
How does this happen?
Here's the chemistry. Initially when a surface is below 100 degrees C, the water/liquid acts normally, flattens out and slowly evaporates. As the temperature increases, you hear a hiss and it evaporates quickly. This is probably something you see and hear all the time if you've been cooking for a long time. Once the temperate reaches passed the Leidenfrost point (a temperature significantly hotter than the liquid's boiling point), the fun stuff happens. Here, as the liquid reaches the surface an insulatated vapor layer is produced that keeps it from boiling rapidly and the droplet sits on top. These droplets bunch up into small balls and jump around. But like with all things this has a limit. The higher and higher you increase the temperature after this point, this effect isn't seen anymore and the droplets evaporate super quick. So try to catch this effect next time you're in the kitchen.
This effect has been used to help develop high sensitivity mass spectrometry under ambient conditions (room temperature and normal pressure). If the droplets are levitating, the molecules aren't released and the droplet is highly concentrated. When ionization occurs, all of the molecules are released in a short amount of time, giving a more sensitive detection method. That's important so we can be able to detect lower concentrations of molecules in smaller volumes.
Here's a link to a video so you guys can see this effect in action.
See you all next month for another Macademics post!
-The Chemist
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