The Science of Superfluids

In a typical chemistry class, if you were asked how many states were there, you would answer three- liquids, solids, and gases. However, in reality, there are much more states, such as plasma and Bose-Einstein condensates. However, there is one state that I found really cool- the state of superfluids.

So how do superfluids occur? We can first begin off with the discovery of superfluids, by two scientists who were cooling liquid helium to near absolute zero. Technically, in an ordinary element, if cooled to near absolute zero, it would become a Bose-Einstein condensate, in which particles overlap each other. However, helium is special in that because it is a noble gas, the attractions between particles are so weak that it has the ability to stay a liquid even when cooled near absolute zero. Obviously, this gives the liquid some really special properties- just check out this video below:

As you can see, superfluids has freaky properties. It can dribble through molecular cracks, climb up over the sides of a container, and remain motionless when a container is spun. So how is this possible? Well, let’s see what defines a superfluid.  A superfluid is any type of fluid that has zero viscosity. Viscosity is the resistance to flow in a fluid, and this resistance is caused by the internal collison/friction between molecules of that fluid. For example, honey has a higher viscosity than water; it is more “thick” and less flow-able. This is due to the internal resistance in honey. All liquids have at least some of this resistance; that is except for superfluids.

So, why do superfluids not have this resistance while other liquids do? It has to do with the temperature. Remember, superfluids have a near-absolute zero temperature. In a typical element, this would result in a solid Bose-Einstein condensate, but for certain elements like helium, they have the special ability to remain a liquid. This does not mean that it doesn’t have Bose-Einstein condensate properties; in other words, superfluids are in a sense liquid Bose-Einstein condensates. A characteristic of these condensates is that all the particles overlap each other to become on super big particle. In a way, there are no such things as particles anymore, but rather just one big thing. This property also occurs in superfluids, which again, are like liquid condensates. So if one “particle” moves, than all the other particles moves too. It’s as if the liquid moves as one. And if this is so, then think about it- there is no internal resistance and thus no viscosity.

This would then explain the superfluid property of staying motionless when the container is spun. If one particle is not moving, then all the other particles are also not moving because the fluid acts as one. (Also, another similar property is if the fluid is spinning, it will keep on spinning forever, because what causes fluids to stop spinning is the internal collisions between particles.) But then how about the property of being able to crawl up the walls of a container? To begin, all liquids have a certain amount of attraction to the sides of a container due to attraction between particles. The liquid in a sense coats the inner surface of the solid container. However, the liquid’s internal friction limits how far the coating may spread. The more friction, the less coating. But with a frictionless superfluid, the coating in a sense goes unlimited, such that it will go over the edges of the container and even defy gravity (gravity on earth is relatively weak, by the way).

For the property of superfluids being able to seep through molecular cracks, however, I do not have an explanation for that. If you do, then I would really like to know so just contact me on the Contacts Page. All in all, superfluids are wonderful scientific things to study. Here are some links that can reinforce your knowledge of superfluids (below). You should check out more superfluid Youtube videos, too.

Scientific American- Strange But True: Superfluid Helium Can Climb Walls                                                                                                                                                                                                          Very Hot, Very Cold, Superfluids Demonstrate the Strangeness of Atoms                                                                                                                                                                                                           Exploring the Superfluid Core of a Neutron Star                                                                                                                                                                                                                                             Wikipedia- Superfluidity

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