Ferrofluid
dark matter
Ferrofluid is an opaque colloidal material composed of nanoscale ferromagnetic particles coated with an anti-clumping surfactant and suspended in a carrier fluid. The iron particles in ferrofluid are so small that they never settle and remain suspended due to Brownian motion. Ferrofluid becomes magnetized in the presence of a magnetic field and its form accommodates a minimal energy state, often appearing as a spiky, yet cohesive black fluid.
With the behaviors of ferrofluid offering a range of possibilities, it is unsurprising that ferrofluids are currently used in a variety of applications. They create seals around spinning drive shafts in hard disks. They are used as semi-active dampers in mechanical and aerospace applications. They can be used as tunable optical filters and in heat dissipation apparatuses. Ferrofluids are often used in designed objects for their novel behaviors - with products ranging from desk toys to ferrofluid timepieces. Due to laws of electromagnetism, it is even possible to use ferrofluids to translate mechanical vibrations into electrical current.
Ferrofluids may hold value in architectural applications as well. While it is a messy, oil-based liquid and it generally takes on an amorphous, low-resolution form, we imagine its passive response to a magnetic field can be leveraged as a low-energy way to control light transmission.
Innovations such as dichromic smart glass modulate glass transparency and opacity on demand, but there are enormous financial and energy costs associated with this technology. Controlling ferrofluid at an architectural scale would likely require massive amounts of ferrofluid, enormous electric power and many bulky electromagnets. While further research is required, it is likely that the field strength at this scale could interfere with metal objects in the room - from ceiling fans to pacemakers. We believe there may be a low-cost, energy-efficient solution that lies somewhere in between - something that embraces the scale of permanent rare earth magnets and something that exists as an array of smaller scale modules.
Because glass has a polar chemical structure and tends to have an imperfect surface, it is important that ferrofluid displays are well-coated in a polar solution, evenly protecting the glass from the nonpolar ferrofluid. Without a polar solvent, iron nanoparticles in the ferrofluid will stick on the glass surface and stain the display.
Roche Labs prepared several vials of ferrofluid for testing - each with between 6 and 20 mL of ferrofluid in 125 mL bottles (roughly 3” x 1.5” cylindrical bottles) filled with a polar solvent. In our lab tests, we soaked the bottles with salt water for several days before adding the ferrofluid. We also made samples using 70% isopropyl alcohol, in which the ferrofluid exhibited a slightly different minimal energy form. While these solvents significantly mitigated surface stains, we have yet to explore potentially more effective solvents. Concept Zero uses a proprietary solution in their impeccable ferrofluid displays and offers guidance on steps to replicate their product.
As can be seen in the image to the left, when the vials are oriented horizontally, the ferrofluid covers the bottom of the vial and significantly impedes light transmission. When a Neodymium rare earth magnet is placed at the end of the vial, the ferrofluid collects around the magnet and light penetrates through the glass container. It should be noted that the cylindrical geometry of the vial influences the light transmitted at a specific angle. This characteristic of glass containers can be designed to high specification in an end product to achieve a desired illusion. Isolating and controlling smaller quantities of ferrofluid within a designed glass enclosure could allow for an amplified light transmission modulation effect.
Our testing also revealed how a 25 Kg pull force electromagnet compares to a rare earth magnet. The magnetic field produced is far weaker than that of the Neodymium magnet. In fact, it is not even strong enough to draw all of the ferrofluid to one end of the horizontally-oriented vial. One surprising result was achieved - when the vials of ferrofluid in salt water are shaken, the ferrofluid disperses into tiny suspended droplets that effectively make the vial opaque. When a magnet is introduced, the droplets consolidate around the magnet. This effect can be seen well in the footage above.
These tests offer much insight into potential opportunities for scaling this behavior. First, we noticed the significant disparity in magnetic field strength between a 25 Kg electromagnet and a small rare earth magnet. The electromagnet, while digitally controllable, offers a significantly weaker magnetic field. Second, we note that magnetic fields do not get locally stronger when additional magnets are coupled. A single ⅜” thick ½” diameter rare earth magnet is strong enough to pull the ferrofluid to one side of the vials in our samples. Lastly, we see a marked difference in ferrofluidic behavior when isopropyl alcohol is used as a suspension fluid compared to saltwater. The ferrofluid in the isopropyl alcohol disperses and rests in a flat pool on the bottom of the vial, while in salt water some samples tend to remain in a cohesive blob form. The alcohol also creates a more pure, spiked geometry when the magnet is introduced. However, the alcohol also quickly becomes discolored. We have yet to determine if this is a breakdown in the ferromagnetic particles or the anti-clumping surfactant.
We suggest that other solvents and different ratios of ferrofluid to solvent be explored. In terms of practical applications, the behavior exhibited in this experiment offers a passive mechanism of modulating light transmission through a container. It can be imagined that this apparatus exists as a matrix of ferrofluid vials. These vials, typically opaque due to ferrofluid collecting on the bottom, are actuated by an armature of small rare earth magnets that, when lowered into position, draws ferrofluid to one end of each of the vials, illuminating the space beneath this canopy.
PI Sam Golini
Production William Kavanagh
Management and Media Gioia Connell