Fun with ferripaste
When is the last time you got your hands dirty with a backyard science experiment? I decided I was long overdue and wanted to try my very best to make a ferrofluid-esque material. Credit for this experimental recipe goes to the YouTube channel Brainiac75, and this video where the host walks through his scientific process of developing his creation, which he calls ferripaste.
Ferro fluid may be a term you are familiar with. Maybe you’ve seen people making fantastic shapes with it on YouTube. The incredible ability this substance has to seemingly defy gravity with its spikes comes from microscopic magnetic particles, and fluid dynamic properties of the liquid.
The Ferro fluid is a liquid and will behave like a liquid until a magnet enters the scene. The magnetic metal particles are very small, generally particles in a colloidal liquid are between 10 and 100 nanometers. While the surfactant in the fluid prevents the metal atoms from binding to each other, the Ferro fluid is experiencing a large surface tension which allows it to hold its shape. There’s also the ever-present force of gravity pulling the larger particles down, and Van der Waals forces contributing to the liquid cohesion. So when you move a magnet near the Ferro fluid, you will see the liquid bunch up into spikes, revealing the shape of the magnetic field it is experiencing.
Ferrofluid was originally developed to be incorporated into rocket fuel that could be directed without the influence of gravity. That was not meant to be, as Ferro fluids have contaminants that cannot be introduced into a rocket engine. Instead, Ferro fluids are being used for their great ability to create magnetic seals when coupled with a magnet. You can find Ferro fluids in spinning drive shafts where they function as liquid O-rings and eliminate much of the friction a mechanical seal might experience. They are also used in speakers. Traditionally, solid dampers would provide suspension for moving voice coils, but when replaced with Ferro fluids, the system vibration is reduced along with energy consumption.
Other non-fluid materials can have properties that are affected by a magnetic field, like magnetorheological elastomers. MechSE Professor Katie Matlack is currently conducting research involving these materials that have potential to be used by the U.S. Air Force.
In stark contrast, my experiment was absolutely not funded by the Air Force Office of Scientific Research like Professor Matlack. In fact, this was a comparatively low-budget endeavor when we think about the price of commercial ferrofluids that can cost upward of $100 per container.
I’m not sure if this is a surprise to anyone at this point, but you can find pretty much any item you can dream up on the internet. To make this experiment happen, I bought Synthetic Black Iron Oxide, also called magnetite (Fe3O4), and one surprisingly strong neodymium magnet off of Amazon. I thought my parents would have some fun doing this experiment with me, so we made it a family thing and my dad contributed to the materials list with SAE 10W30 Motor Oil, which acted as both the carrier fluid and surfactant for our creation.
[Quick aside on the naming scheme of engine oil. In case you ever wondered what the numbers mean, they correspond to the SAE Viscosity Grade, which ranges from 0 to 50. The first number in the oil naming scheme refers to the viscosity of the oil at cold start of the vehicle, and the second number refers to the viscosity of the oil at a running temperature of 100°C. A lower number means the motor oil is less resistant to shear force, and will be thinner.]
Back to the experiment. In his video, Brainiac75 had a scientific process where he measured the amount of magnetite and motor oil he mixed together. Most ferrofluids are composed of about 5% magnetic particles, 10% surfactant and 85% carrier fluid. In all honesty, my parents and I didn’t have a gram weigh scale handy, and instead opted to carefully eyeball the ratios.
That said, I’m happy with the results! You can see the ferrofluid-like spikes that formed when we put the magnet on the outside of the container, and the gifs show that the fluid really did move around as we moved the magnet. However, this creation is much more viscous than the ferrofluids you may be familiar with. Also, because we used magnetite as our particle, which is a ferrite, this goop is ferrimagnetic instead of ferromagnetic. All in all, my review that no one asked for is 10/10, and I would absolutely play with ferripaste again.