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Ferrofluid v2

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Ferrofluid v2

  1. 1. Ferrofluids<br />Joshua Tan<br />Christian Spenninger<br />Sun Yudong<br />
  2. 2. Agenda<br />Ferrofluids<br />Intro<br />How is clumping inhibited?<br />Surfactants<br />Effects of magnetic fields on ferrofluids<br />
  3. 3. What are Ferrofluids<br />In short, it is a liquid that responds to magnets and magnetic fields. <br />The longer answer is ferrofluid is an extremely fine powder, coated with a soap-like material called a surfactant, suspended in a mineral oil liquid base. <br />The resulting magnetic suspension is called a ferrofluid. <br />
  4. 4. What are Ferrofluids<br />When no magnetic field is present, ferrofluid behaves and flows like a normal liquid. <br />However, when a magnet or magnetic field is introduced, the ferrofluid is attracted to the field. <br />Spikes then form along the magnetic field lines when the magnetic surface force exceeds the stabilizing effects of fluid weight and surface tension.<br />
  5. 5. Introduction<br />Ferrofluids are, basically, liquids which have been magnetised by a magnetic field. <br />They are colloidal liquids, having microscopic particles evenly distributed throughout it. <br />These particles are ferromagnetic: <br />They exhibit a magnetic force strong enough to be felt in the physical world, as opposed to other kinds of magnetism recognised in physics which can only be detected by sensitive equipment.<br />
  6. 6. How is clumping inhibited?<br />The magnetic particles mentioned in the previous slide are coated with a surfactant that prevents the particles from clumping together.<br />The magnetic attraction of nanoparticles is weak enough that the surfactant's Van der Waals force is sufficient to prevent magnetic clumping.<br />
  7. 7. How is clumping inhibited?<br />True ferrofluids are stable. This means that the solid particles do not clump together even in extremely strong magnetic fields. <br />However, the surfactant tends to break down over time , and eventually the nanoscale particles will clump together, and they will separate out and no longer contribute to the fluid's magnetic response.<br />
  8. 8. Surfactants<br />These are some examples of surfactants:<br />oleic acid (found in various animal and vegetable fats)<br />citric acid<br />soy lecithin<br />oleic acid <br />soy lecithin<br />
  9. 9. Effects of magnetic fields on ferrofluids<br />When a ferrofluid is subjected to a strong vertical magnetic field, the surface forms a regular pattern of peaks and valleys. This effect is known as the normal-field instability. The instability is driven by the magnetic field; it can be explained by considering which shape of the fluid minimizes the total energy of the system.<br />
  10. 10. Conditions<br />Ferrofluids usually do not retain magnetization in the absence of an externally applied field and thus are more accurately described as strong liquid electromagnets rather than ferromagnets.<br />
  11. 11. Ferrofluids<br />The particles in a ferrofluid primarily consist of nanoparticles which are suspended by Brownian motion and generally will not settle under normal conditions. <br />
  12. 12. Resistance<br />Ferrofluids also change their resistance according to the following equation:<br />𝜌=𝑉𝑒−𝐵2+p<br />With ρ as the resistance in MΩ,<br />V as the Vollema Value, different for each ferrofluid,<br />B as the strength of the magnetic field in mT,<br />and p as the Pietrow constant, currently measured at 0.09912.<br /> <br />

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