by Alex Mazursky
Difficulty: Intermediate
Duration: 1-2 hrs
Introduction
Magnetic soft materials are a fascinating class of materials that can be used in a variety of applications, from interactive devices to shape-changing robots. These materials consist of a stretchy polymer matrix and embedded magnetic particles. The polymer provides elasticity, while the magnetic particles enable the material's response to applied magnetic fields. In this tutorial, we will discuss the fabrication process for making magnetic soft materials and provide some tips for maximizing their performance. This tutorial is based around our findings from our CHI 2021 paper, MagnetIO, but can be adapted into new designs with a little creativity!
Prerequisite and background topics
Prior to starting the tutorial, you can try familiarizing yourself with the following prerequisite topics and terminology by browsing the resources linked under each item.
Democratizing magnetic soft materials fabrication (more nuance than this tutorial)
Materials and Equipment Required
Elastomer mix (e.g., a silicone like Ecoflex or Dragonskin, ~$20/lb which goes a long way for small parts)
Magnetic particles (e.g., neodymium powder, ~$15/lb)
2x Strong permanent magnets (~$15/magnet)
Mold (e.g., a 3D-printed shape to cast, CAD files shown here available on Github)
Mixing container and stirring tool
Optional: dehydrator (accelerates silicone curing)
Instructions
1. Mix the polymer and magnetic particles
Mix the silicone and magnetic particles together by hand for 10 minutes (cross-check this time with the pot life of your polymer).
2. Cast the mixture into a mold
After mixing the polymer and magnetic particles, the mixture is cast into a 3D printed mold to shape the magnet. The mold is then held between two strong permanent magnets. This strong magnetic field magnetizes and aligns the polarities of the individual particles, resulting in a composite with a strong, permanent magnetic field while remaining flexible due to the silicone holding it together. Be very careful on this step, strong magnets can rapidly attract and shatter or pinch the skin. Magnets should always be handled with care.
3. Cure the mixture in a strong magnetic field
To maximize the magnetic field strength and produce strong response to external fields, we used an NdFeB weight concentration of 80%. After the magnetic composite has cured, it may be removed from the mold. While the magnet may be stiff initially, it may be softened via stress softening, i.e., stretching, bending, etc. Note that optionally placing the mold inside a dehydrator accelerates the curing time.
(Optional) 4. Make the mechanism and assemble the interactive patch
In the case of MagnetIO, we also made a mechanism using pure silicone, which functioned as a spring for the magnet to vibrate. After both the silicone mechanism and soft magnets have cured, the interactive patch is assembled by adhering the soft magnets to the silicone mechanism.
Conclusion
In this tutorial, we have discussed the fabrication process for making magnetic soft materials, which consist of a polymer matrix and embedded magnetic particles. By following these simple steps, you can create your own!
Variations & Things to try
Aligning the particles along different directions
Try elastomers of different softness or vary the percentage of magnetic powder
Embed multiple polarities into a single material to create a complex response
Experiment with different silicone mechanism designs, such as bistable springs
Post-requisite topics & Going beyond
Read more about the use of magnetic soft materials in interactive devices and shape-changing robots.