ferrofluid v2

13
Ferrofluids Joshua Tan Christian Spenninger Sun Yudong

Upload: yudong-sun

Post on 25-May-2015

1.542 views

Category:

Education


0 download

TRANSCRIPT

Page 1: Ferrofluid v2

FerrofluidsJoshua Tan

Christian Spenninger

Sun Yudong

Page 2: Ferrofluid v2

AgendaFerrofluids

IntroHow is clumping inhibited?SurfactantsEffects of magnetic fields on ferrofluids

Page 3: Ferrofluid v2

What are FerrofluidsIn short, it is a liquid that responds to magnets and

magnetic fields. 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.

The resulting magnetic suspension is called a ferrofluid.

Page 4: Ferrofluid v2

What are FerrofluidsWhen no magnetic field is present, ferrofluid behaves

and flows like a normal liquid. However, when a magnet or magnetic field is introduced,

the ferrofluid is attracted to the field. Spikes then form along the magnetic field lines when the

magnetic surface force exceeds the stabilizing effects of fluid weight and surface tension.

Page 5: Ferrofluid v2

IntroductionFerrofluids are, basically, liquids which have been

magnetised by a magnetic field. They are colloidal liquids, having microscopic particles

evenly distributed throughout it. These particles are ferromagnetic:

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.

Page 6: Ferrofluid v2

How is clumping inhibited?The magnetic particles

mentioned in the previous slide are coated with a surfactant that prevents the particles from clumping together.

The magnetic attraction of nanoparticles is weak enough that the surfactant's Van der Waals force is sufficient to prevent magnetic clumping.

Page 7: Ferrofluid v2

How is clumping inhibited?True ferrofluids are stable. This means that the solid

particles do not clump together even in extremely strong magnetic fields.

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.

Page 8: Ferrofluid v2

SurfactantsThese are some examples of surfactants:

oleic acid (found in various animal and vegetable fats)citric acidsoy lecithin

oleic acid soy lecithin

Page 9: Ferrofluid v2

Effects of magnetic fields on ferrofluidsWhen 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.

Page 10: Ferrofluid v2

ConditionsFerrofluids 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.

Page 11: Ferrofluid v2

FerrofluidsThe particles in a ferrofluid primarily consist of

nanoparticles which are suspended by Brownian motion and generally will not settle under normal conditions.

Page 12: Ferrofluid v2

ResistanceFerrofluids also change their resistance according to the

following equation:

With ρ as the resistance in MΩ,V as the Vollema Value, different for each ferrofluid,B as the strength of the magnetic field in mT,and p as the Pietrow constant, currently measured at

0.09912.

Page 13: Ferrofluid v2