Lecture 22: Nucleation in First Order (Abrupt) Phase Transitions
Today we discuss nucleation in first order (abrupt) phase transitions. The ice crystals in our supercooled bottle of water formed through nucleation -- tiny ice crystals grew larger over time. The arctic cod is a supercooled fish, living in water too salty to freeze even though it's at -1.9 degrees Celsius! The reason the fish doesn't freeze solid is due to antifreeze glycoproteins, which inhibit the growth of nucleated ice crystals. We calculate the energy barriers to nucleation at the liquid-gas transiton, and find that a nucleated liquid bubble in the gas phase must be large enough before it will turn the whole substance liquid. If it's too small, the bubble is unstable and converts back into gas.
We also discuss: Slushy ice -- where is that on our phase diagram? Surface tension and faceting in crystals. Plant-eating bacteria which secrete enzymes that encourage ice nucleation on plants. And quite a bit about how snowflakes form.
Much of today is from Jim Sethna's statistical mechanics book, and the part about snowflakes and ice formation is from research at my alma mater, Caltech, as presented at www.snowcrystals.com.