Ferrofluid

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Physics, Chemistry,

Engineering:

Nanoparticles, Superparamagnetism
Grade Range: Elementary School,

Middle School, High School

Format: Hands-on

Students of all ages will enjoy playing with the vial of ferrfluid, and the topic matter is broad enough to be applicable at all grade levels. Be sure that students don't shake or drop the vial!

Contents

Materials

  • Ferrofluid with Magnet
  • Optional: Million Dot Book
  • Optional: Ruler or Meter Stick

Safety Precautions

Please read the General Safety section of the Demonstration Safety page before performing this demonstration.

Demonstration

  1. Allow students to come up and play with the ferrofluid. This is a show-and-tell type of demonstration, so ask them questions about the ferrofluid while they play with it, and provide explanations after taking any answers. The Million Dot Book and the ruler or meter stick can be helpful for explaining the concept of a nanoparticle. Some good questions to ask the students are:
    • What do they think the black liquid is made of?
    • How small are the magnetic particles in the liquid?
    • Why does the liquid spike up? Why doesn't it ball up instead?

Why This Works

Ferrofluids are fluids that become strongly magnetized when exposed to a magnetic field. These fluids have iron or iron-rich nanoparticles suspended in a solution that prevents them from clumping together. Nanoparticles are particles that are between one and ten billionths of a meter in diameter. You can fit about three atoms into a single nanometer, so a nanoparticle will only have three to thirty atoms in it. The Million Dot Book can help students visualize how small a nanoparticle is. The book contains one million dots in it, so each dot only makes up one millionth of the book. If we had one thousand of the Million Dot Books, then they would have one billion dots between them, each dot representing only one billionth of all the dots. The ruler or meter stick also help: a single millimeter contains one million nanometers, so students can try to visualize cutting a single millimeter into one million pieces.

Ferrofluids are strongly magnetized when exposed to a magnetic field, and become paramagnetic while within a magnetic field. Paramagnetism is when a material becomes magnetic when placed in a magnetic field, and it is attracted to the magnetic field. When taken out of the magnetic field, the material will no longer be magnetic. Paramagnetism differs from ferromagnetism because a paramagnet cannot stay magnetic outside of a magnetic field, whereas a ferromagnet can continue to be magnetic when removed from a magnetic field. Ferrofluid, however, is unique due to how strongly it becomes paramagnetic. A ferrofluid can mimic the strength of the magnetic field it is exposed to, making the entire ferrofluid as strong as the original source. This effect is known as Superparamagnetism.

Ferrofluids are commonly used in electronics to provide cushioning from friction and to keep dust and dirt out of seals on spinning parts. This is due to two different properties with ferrofluids: their behavior as a non-newtonian fluid, and the normal field instability they show with their spikes. A Non-Newtonian Fluid is a fluid that can behave as a solid when under certain circumstances. Ferrofluids, when under a strong magnetic field, will behave like a solid when undisturbed and act as a liquid when agitated. Normal Field Instability refers to how the ferrofluid's magnetic field arranges itself within a magnetic fluid. When the field is trying to travel upwards, it has to fight against gravity and the surface tension of the liquid. By creating the spikes, the ferrofluid can maximize the magnetic field into the spikes and allow gravity and surface tension to take over in the valleys between them. The effects work together when a ferrofluid is being used as a sealant; The undisturbed fluid on the outside will spike up and behave as a solid, preventing dirt and dust from getting inside, while the fluid beneath the surface is free to move, and reduces friction between the moving parts.

Additional Information

  • Nanoparticles are smaller than the microparticles used in an MRI. Microparticles are one millionth of a meter, and nanoparticles are one billionth of a meter.
  • This demonstration pairs well with Oobleck and the Meissner Effect
  • This demonstration pairs well with the demonstrations used in the Quantum Mechanics Show.
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