Hands-on Activity Magic Magnetic Fluid

Learning Objectives

After this activity, students should be able to:

• Explain magnetism theory.
• Relate differences in large scale magnetic materials and nano-magnetic materials.
• Describe the unique behavior of ferrofluids under magnetic fields.
• Describe applications and uses for ferrofluids.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 1 container of red liquid food coloring
• 25 ml test tube, with threaded lid
• 1 0.5" diameter x 0.250" thick rare-Earth Neodymium Disc Magnet (available at: https://www.magcraft.com/disc-magnets)
• glass stirring rod or wooden Popsicle stick
• 4" x 6" clear plastic dish
• latex glove
• Liquid Magnets Worksheet, one per student

To share with the entire class:

• 250 ml beaker
• 1 bottle MICR toner powder refill (HP C4127 #27, 500 g bottle available at: https://www.inkowl.com/laser/micr-refill-kits/hp/1-micr-toner-refill-for-use-in-hp-c4127-27-c4129-29-c8061-61/P3305/) NOTE: refill bottle lasts for multiple liquid magnet activities.
• 1 bottle vegetable cooking oil
• computer with Internet access and projector to show students an online video clip

Worksheets and Attachments

Pre-Req Knowledge

Students should have been introduced to basic magnetism principles, including, but not limited to: theory of magnetic domains, Curie temperature, magnetic poles, ferromagnetism, paramagnetism and diamagnetic materials. It is also helpful if students have knowledge of basic chemistry principles, such as: colloids or suspensions, surface tension, and surfactants.

Introduction/Motivation

(Introduce the pop culture television show, Fringe, to students. Ask if they have heard of the TV series and read the Fringe Summary supplemental information sheet to students to facilitate the introduction. Add to this sheet a great summary of the Fringe plot and season at the show's Wikipedia page at https://en.wikipedia.org/wiki/Fringe_(TV_series))

(Show students a portion [at least 10 minutes] of episode #317, "The Day We Died," in which the Fringe team discovers that a murder victim's blood is magnetic. The episode is available for $1.99 at: https://www.youtube.com/watch?v=H8SH5Odx7kA&list=ELFg8HF_XnBEU&index=22.)

(After watching the video, ask students the following questions investigating their knowledge of magnetism and how a liquid can be magnetic:)

• Is magnetic blood or magnetic fluid science fiction or science fact? Have students vote; tally the answers for science fiction or science fact. Do not give any particular answer but proceed to the next question.
• How can a liquid be magnetic? Encourage student participation and critical thinking---to think outside of the box and come up with supplemental ideas: Curie point, traditional magnetic materials, melting points etc.
• What are ferrofluids? Let students discuss briefly, then provide a short explanation of ferrofluid ingredients and functionality. For this explanation, visual aids might be useful. (NOTE: Ferrofluids applications are listed in the Background section.)

(Conclude the introduction with general description of the activity, as described in the activity Summary.

Procedure

Background

Most materials fall into three categories of magnetic materials: Paramagnetic (Al, Cr, K, Mg, Mn, Na), diamagnetic (Cu, Bi, C, Ag, Au, Pb, Zn) and ferromagnetic (Fe, Ni, Co, Gd, Dy, Nd). Paramagnetic materials contain permanent dipole moments (induced force x charge separation distance), which align under an external magnetic field but are counteracted by thermal vibrations resulting in a weak magnetic attraction. Under conditions of extremely high magnetic fields and low temperature, paramagnetic materials may behave similar to ferromagnetic materials. Diamagnetic materials do not have any permanent dipole moments, but induced dipole moments align opposite to the external magnetic field. Under these conditions, the net field is lower than the external field.

Amongst these categories, ferromagnetic materials exhibit the largest magnetic permeability. As the name suggests, ferrofluids are composed of ferromagnetic particles, surfactant (laundry detergent, dish soap), and carrier fluid (kerosene, vegetable oil, mineral oil). Ferromagnetic particles are used because of their large magnetic permeability compared to other classifications of magnets. Essentially, the resultant magnetic field is orders of magnitude larger than the induced magnetic field. This becomes important when manipulating ferrofluids under moderate and controlled magnetic fields.

Typical ferromagnetic materials consist of iron-, nickel- and cobalt-based metals and occasional rare Earth materials such as neodymium and chromium and iron oxide compounds, such as magnetite (Fe₃O₄). Ferromagnetism is caused by a long-range atomic scale ordering that causes unpaired electrons to align parallel with each other in a domain. These domains, or regions (~1 mm linear dimension), of magnetic alignment are randomly oriented and confined within the bulk material leading to a net magnetic field of zero. However, under an external magnetic field, these domains align causing an amplification of the applied magnetic field. These domains created under atomic scale long-range ordering may span over large numbers of atoms. However, to make a ferromagnetic material fluid for our purposes would require melting the metal. Under such conditions, typical ferromagnetic alloys have melting points in excess of the point when ferromagnetic properties transition to paramagnetic. This transition is denoted as the Curie point of temperature.

For materials engineers, these principles become important when developing magnetic fluids. The challenge is making a fluid magnetic without exceeding the materials Curie point. Engineers have developed paramagnetic salt solutions for magnetic fluids. These fluids exhibited less than adequate magnetic permeability because of reduced interaction with external magnetic fields. However, as explained above, low temperature and excess magnetic fields lead to near ferromagnetic interactions, but limit applicable use because of these restrictions. In general, paramagnetic materials have a magnetic permeability far less than a ferromagnetic material. Under these conditions ferromagnetic nanomaterials become increasingly important.

To meet such a challenge, engineers have developed ferromagnetic nanoparticles. These particles are approximately 10 nm in diameter but small enough to be suspended in various carrier fluids (kerosene, vegetable oil or mineral oil). Such suspension could be considered colloidal, meaning fine particles remain suspended in a liquid where settling does not occur over a long period of time. Additionally, the size of each nanoparticle is on the order of a few atoms in diameter. This creates a single magnetic domain particle—meaning, each nanoparticle is its own permanent magnet suspended in the carrier fluid. With a suitable surfactant to prevent particle agglomeration, the suspension can then be manipulated under a controlled moderate magnetic field.

These magnetic fluids have received considerable attention over the last few decades with applications geared towards rotary shaft sealing and audible speaker cooling systems. More recently, researchers are applying ferrofluids to cancer treatment and drug delivery systems. Cancer treatment has been proposed through methods utilizing the heating effect of alternating magnetic fields and the energy lost from such cycling. For drug delivery systems, magnetic drugs with a suitable surfactant are injected into the blood stream and manipulated with external magnetic fields for localizing treatment. These medical treatment advancements are only limited by the ability to create nontoxic, biologically compatible, magnetic particles.

Today, you are acting as materials engineers, creating your own ferrofluids. You are challenged to make magnetic fluids that you can manipulate. You'll use your observation skills and newly found knowledge of ferrofluids to complete the worksheet.

Before the Activity

• Placed all lab supplies in a location that is easily accessible to students.
• Mix ferrofluid according to the instructions below, and distribute equal portions to each group. Provide a glass stirring rod or Popsicle stick for students to use if ingredients begin to separate. (Alternatively, if time permits, have students measure and mix their own ferrofluids.)
• Make copies of the Liquid Magnets Worksheet, one per student.

Ferrofluid Recipe

1. Pour 50 ml of MICR toner into a 250 ml beaker.
2. Add 30 ml of vegetable oil in the same 250 ml beaker.
3. Use a glass rod or wooden stick to stir the mixture until it has a light, smooth texture.
4. Carefully, pour 10-15 ml of fluid in a 25 ml test tube and secure the lid.

With the Students

1. Divide the class into groups of three or four students each.
2. Review with students the supplies available to them for the activity (however, do not give them the supplies yet, so as to not distract them during delivery of instructions).

Part 1: Concepts

1. In their groups, have students complete the concept questions on the Liquid Magnets Worksheet.
2. Once groups have completed the questions, proceed to Part 2.

Part 2: Magnetic Fluid (Blood) Manipulation

1. Direct students to place the magnet under the center of the clear plastic dish and pour a small amount of fluid from your test tube in the dish, covering the area that the magnet occupies beneath and outside the dish.
2. Add two drops of red food coloring and mix using the magnet outside the dish. This completes magnetic blood fabrication.
3. Have students use their hands to manipulate the magnet and fluid, outside the dish, making squares, triangles and circles. Direct students to remove the magnet from under the plastic dish and observe how the fluid behaves. Fairly quickly, place the magnet back under the dish, and observe how the fluid (blood) behaves.
4. Have students place the magnet, outside the dish, under the fluid as above and begin touching fluid with a latex glove. Ask them if they can spin their fluid (blood)? (The purpose of this challenge is to show students how the fluid, when under a magnetic field, becomes more viscous, contrasting with typical fluid properties.)
5. Direct student groups to complete their worksheets.
6. Have students clean up their plastic dishes by wiping the magnetic fluid with paper towels, making sure no fluid residue is present in the dish.
7. Ask students to clean up their "lab" areas and any remaining activity supplies.

Vocabulary/Definitions

colloidal: A chemical system in which a continuous liquid phase exists with a solid phase suspended in the liquid.

Curie point: Temperature at which ferromagnetism is lost due to excessive thermal agitation.

diamagnetic: A substance containing no unpaired electrons and not attracted to a magnetic field.

domain: A region where unpaired electrons are aligned parallel, creating a magnetic field.

ferrofluid: Ferromagnetic particles suspended in a carrier fluid with the aid of a surfactant.

ferromagnetic: Long-range ordering phenomenon at the atomic level that cause unpaired electron spins to line up parallel with each other in a domain.

paramagnetic: Very weakly attracted by the poles of a magnet, but not retaining any permanent magnetism.

surface tension: An increased attraction of molecules at the surface of a liquid resulting from forces of attraction on fewer sides of the molecules.

surfactant: A chemical that acts as a wetting agent to lower the surface tension of a liquid and allow for spreadability.

Assessment

Pre-Activity Assessment

Investigating Questions: Ask students the questions provided in the Introduction / Motivation section. These questions are designed to initiate students' thinking of magnetic fluids. Answers are embedded in this activity write-up; however, encourage students to be creative in their answers and use their own descriptive words.

Activity Embedded Assessment

Worksheet: Use the Liquid Magnets Worksheet as a teaching aid for students to record all observations during the activity. Additionally, questions are included to stimulate students' critical thinking of this topic. Students are asked to answer questions related to magnetism with a main focus on importance of scientific observations. Require students to finish the entire worksheet in the time allotted.

Post-Activity Assessment

Take Home Research Paper: Have students research the fundamental differences between magnetic fluids and traditional bulk magnetic solids by each reviewing a minimum of two applications in which ferrofluids may be useful. Direct students to use web-based resources and/or any additional physics text or prior knowledge of magnetism to identify fundamental differences and applications. Require their research papers to include concise introductions (problem statement), fundamental content review, explanations of differences and technology application reviews. Suggest the papers be approximately two pages of double spaced text, including figures and tables. Use the following grading rubric:

Introduction:

• Are research objectives introduced in a concise manner? – 10 pts
• Are objective clear to the reader? – 10 pts

Content Review:

• Is a comprehensive overview of magnetism content provided? – 15 pts

- Key terms included, such as: Curie point, domains, poles, electrons, spins? – 5 pts

- Key terms explanation provided as necessary? – 10 pts

• Are concepts that apply to each type of magnetic solid or liquid material listed? – 5 pts

Magnetic Differences:

• Are fundamental differences between liquid and bulk solid magnets identified? – 10 pts
• Is content from online resources, library or class used to support claims for differences? – 10 pts

Technology Applications:

• Are two applications described? – 5 pts
• Are technology applications introduced and explained? – 10 pts
• Are reference material and prior knowledge used to support explanations? – 5 pts

Additional Criteria:

• Is correct grammer and sentence structure used throughout paper? – 20 pts

Possible References:

• http://mrsec.wisc.edu/Edetc/background/ferrofluid/index.html
• http://en.wikipedia.org/wiki/Ferrofluid
• http://en.wikipedia.org/wiki/Ferromagnetism

Safety Issues

• Ingredients used in this activity are harmless when exposed to skin in standard form. However, with all laboratory practices, make sure to read the appropriate material safety data sheet (MSDS) prior to conducting the activity. (NOTE: Request the MSDS through the product manufacturer or supplier.)
• All students should wear goggles and aprons when conducting this activity.
• Toner may stain skin and clothes; use latex gloves for cleanliness even though they are not necessary for safety.

Troubleshooting Tips

If magnets are not strong enough, the fluid will not show individual magnetic "spikes," but will still control the fluid. If this occurs, have students use gravity to move fluid around the dish, and direct fluid flow with the magnet outside the sides of the dish. This achieves the same educational objectives without the flare.

Additional Multimedia Support

Fringe episode #317, "The Day We Died," https://www.youtube.com/watch?v=H8SH5Odx7kA&list=ELFg8HF_XnBEU&index=22

References

Copyright

Contributors

Supporting Program

Acknowledgements

This digital library content was developed by the University of Houston's College of Engineering under National Science Foundation GK-12 grant number DGE 0840889. However, these contents do not necessarily represent the policies of the NSF and you should not assume endorsement by the federal government.