Commercial Ferrofluid

Introduction

A magnetic liquid, also known as a ferrofluid, may seem like a space-age concept. That’s because it is—the idea was conceived by NASA in the 1960s to control the flow of liquid fuels in space! Ferrofluid consists of nano-sized magnetic particles suspended in a liquid. This activity provides some exciting ways to demonstrate the unique properties of ferrofluid.

Concepts

• Nanotechnology
• Magnetic properties
• Colloids vs. solutions

Experiment Overview

The purpose of this activity is to demonstrate the unique physical properties of ferrofluid and how its magnetic nanoparticles respond to a magnetic field.

Materials

Safety Precautions

Ferrofluid is a skin and eye irritant and will stain skin and fabric. Use caution when handling the neodymium magnet. These magnets are very strong; keep away from computers and other electronics. They may chip or shatter if dropped. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding.Ferrofluid used in the demonstrations as written may be returned to the bottle and stored for future use. Materials coated in ferrofluid may be wiped clean with paper towels and the paper towels thrown away in the regular trash according to Flinn Suggested Disposal Method #26a.

Prelab Preparation

(Before handling ferrofluid, please read the Tips section.)

1. Place a penny in the bottom of each of two small disposable Petri dishes. 
2. Place a neodymium magnet in a resealable plastic bag under one Petri dish. 
3. Using a disposable pipet, carefully add enough ferrofluid so the ferrofluid forms a dome with spikes over the magnet. Note: Do not add too much ferrofluid or the dome of fluid will mound up too high and not show any spikes. 
4. Keeping the magnet in place under the Petri dish, place the cover on the dish and seal around the circumference of the dish with masking tape. Press the tape firmly against the dish for a good seal. 
5. Carefully remove the magnet from underneath the dish. Note: Once the ferrofluid has been added to the dish it is important to keep the dish level. Ferrofluid will coat the inside surface, and if it comes in contact with the cover of the dish, observations will be difficult, if not impossible. If this happens, let the covered dish stand with a magnet centered underneath until the ferrofluid flows back to the bottom of the dish. This may take up to 10 minutes before the dish is transparent enough to see through and from 30 minutes up to an hour until more detailed observations may be made.
6. In the second Petri dish, measure and add 3 g of iron filings and enough tap water to match the level of ferrofluid in the first dish. Note: Iron filings will not rust as quickly in tap water compared to deionized water. 
7. Place the cover on the second Petri dish and tape to seal.

Procedure

Activity 1—Compare and Contrast Macro- and Nano-sized Iron Particles

1. Show students the two prepared Petri dishes and instruct students to record observations about the contents of each dish. (See Sample Data.)
2. Gently shake the dishes from side to side so students can observe how the contents move. Students should include observations about the relative densities of the penny and the rest of the contents in each dish.
3. While holding the Petri dish with iron filings in one hand and a neodymium magnet inside a plastic bag in the other hand, slowly and carefully bring the magnet up from below the dish to the center of the bottom of the dish, away from the penny. Instruct students to record observations about any differences they see.
4. Repeat step 3 with the ferrofluid Petri dish. Note: BE VERY CAREFUL that the magnet stays under the Petri dish and away from the outer edge of the dish. Bringing the magnet too close to the side of the dish may cause the ferrofluid to leak out.
5. Repeat step 3 with the first Petri dish and move the magnet around so it moves from next to the penny to under the penny. Instruct students to record observations.
6. Repeat step 5 with the ferrofluid Petri dish.

Activity 2—Ferrofluid Sculptures

1. Obtain a clean, small disposable Petri dish, a small steel bolt, and a steel wing nut to fit the bolt.
2. Thread the wing nut onto the end of the bolt just enough so the nut remains on the bolt.
3. Place a neodymium magnet in a resealable plastic bag and set it flat on the demonstration table.
4. Center the Petri dish on top of the magnet.
5. Place the nut and bolt assembly in the center of the Petri dish over the magnet (see Figure 1).

6. Have students watch as you slowly and carefully dispense ferrofluid drop-wise onto the wing nut and bolt until 1–2 mL have been dispensed.
7. Instruct students to record their observations. Note: Students close to the demonstration table should wear chemical splash goggles.

Teacher Tips

• Ferrofluid can be messy. Please read the following handling tips: 
  —Always wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron when working with ferrofluid.
  —Covering the work surface with newspaper or paper towels during preparation and cleanup is recommended.
  —When dispensing ferrofluid, gently squeeze the pipet bulb and aim carefully so the ferrofluid does not splatter.
  —Keep any magnets inside a plastic bag to protect them from coming in contact with the ferrofluid.
  —Keeping a strong magnet in a resealable bag under the Petri dish during preparation will help contain the ferrofluid in the center of the dish, preventing it from coating the sides or top of the dish. Remove the magnet when necessary for student observations.
  —Use caution when bringing a magnet close to a dish containing ferrofluid. Ferrofluid may “leap” from the dish if the magnetic field is too close. Always bring a magnet to the dish from below and keep it centered under the dish.
  —Excess ferrofluid may be returned to the bottle and reused. Cap the bottle tightly to prevent evaporation.
  —Remember to wear appropriate personal protective equipment during cleanup. Remove objects from ferrofluid with non-magnetic forceps and throw away or wipe clean with paper towels.

• Use a projection camera, such as Flinn Catalog No. AP7641, so all students may easily see the demonstrations at the same time.
• Iron filings made from a non-rusting alloy are available from Flinn Scientific, Catalog No. I0059. Note: Even non-rusting iron filings will eventually rust if stored in water. After completing Activity 1, absorb the water in the Petri dish with paper towels and spread the filings out on a clean paper towel to dry.
• Repeat Activity 1 without the penny and experiment with other magnet shapes. Magnetic rings and flat, flexible vinyl refrigerator magnets make interesting patterns with the ferrofluid. Place the magnetic side of a vinyl magnet against the bottom of the Petri dish and place a stronger magnet under the vinyl magnet to make the magnetic lines of force more noticeable.
• Experiment with other magnetic objects such as nails, screws, staples, paper clips, etc. to create other ferrofluid sculptures. See how the shape and size of the objects as well as the amount of ferrofluid affect the magnetic patterns.
• Solutions and colloids differ in the size of the particles that are dispersed in the liquid phase. The following table summarizes the properties of solutions, colloids, and suspensions. Notice that the particle size range for each type of mixture is just that, a range, and not an absolute or fixed value.
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• Make your own ferrofluid with Flinn Scientific Ferrofluid Nanotechnology Demonstration kit, Catalog No. AP7118.

Sample Data

Activity 1

Activity 2

As the ferrofluid is dripped onto the wing nut and bolt assembly on top of a magnet, it is attracted to the wings of the nut. Eventually spikes form on the wings. As more ferrofluid is added, the spikes along the bottom of the wings “grow” larger and eventually a drop of ferrofluid falls from the nut into the dish where it is attracted to the base of the bolt.

Discussion

Nanoscience or nanotechnology involves the preparation, characterization and uses of nano-sized particles having dimensions in the 1–100 nm range (1 nm = 1 x 10^–9 m). Nanoparticles have unique physical and chemical properties that are very different from the macroscopic properties of traditional or “bulk” solids. Many of these properties have taken on special importance in recent years as the applications of nanotechnology have been intensively studied. In particular, the electronic, magnetic, and optical properties of nanoparticles have proven to be very useful in the creation of new products using nanotechnology.

Magnetic liquids, also known as ferrofluids, are stable colloids containing nanocrystalline magnetite particles that are about 10 nm in diameter. In the absence of an external magnetic field, the ferrofluid flows and behaves like a “normal” albeit viscous liquid. When a magnet is brought near a dish or vial containing the ferrofluid, the “solid” nanoparticles are attracted to and will “follow” the magnet around the dish or vial. As the magnetite nanoparticles become more concentrated at the magnetic pole, the ferrofluid mounds up, becoming more dense and a penny “floats” on top of the dome. The ferrofluid forms interesting three-dimensional shapes or structures as the magnetic moments of the nanoparticles align themselves with the external magnetic field. Noticeable peaks or spikes in the ferrofluid correspond to the magnetic field lines (see Figure 2). When a magnetic object such as a bolt is placed in a magnetic field, the bolt becomes a temporary magnet with the strongest part of the magnetic field concentrated at the ends. Thus when ferrofluid is added to the bolt, spikes appear on the end of the bolt.

Ferrofluids are more than just an intellectual curiosity. They have innovative commercial or practical applications, including as dampeners or heat sinks in loudspeakers, as seals in high speed computer disk drives, as magnetic inks for laser printers, and even, apparently, as radar-absorbing paints that allow military aircraft to escape radar detection.

References

National Nanotechnology Infrastructure Network, www.nnin.org (accessed October 2010).