Talk:Ferrofluid

I think someone combined two sections that should not be together:

They are used in loudspeakers to sink heat between the voice coil and the magnet assembly, and to damp the movement of the cone. They reside in what would normally be the air gap around the voice coil, held in place by the speaker's magnet. Using electromagnets and sensors, the fluid's viscosity can be controlled dynamically. This allows hundreds of watts of mechanical power to be controlled with a few watts of electrical power, which is much more efficient than other methods of vibration control, such as piezoelectric crystals.

to my understanding, ferrofluid does not change viscosity under different magnetic fields, and is not used in that way to damp speakers. i think MR fluid is used to damp car shocks in that way, but it's not the same kind of damping. - Omegatron 02:49, Jul 8, 2004 (UTC)

Defn:

A ferrofluid is a stable colloidal suspension of ferromagnetic mono-domain particles in a liquid carrier. To avoid agglomeration due to attractive dipole-dipole or Van der Vaals forces each particle is coated by long-chain molecules or by an electrostatic layer (see figure). Due to the smallness of the particles (diameter ~ 10nm) the properties of ferrofluids are substantially affected by thermal Brownian motion. When exposed to a magnetic field, a ferrofluid behaves like a paramagnetic gas of high permeability (Rosensweig).

--Light current 07:58, 4 February 2006 (UTC)

Add

Just added link to MRC page.

Take your pic

I have provided a number of images which I believe to be higher quality and more informative than the ones currently used on the article. Feel free to make use of them. --Gmaxwell 01:19, 13 July 2006 (UTC)

Whoa! — Omegatron 02:33, 13 July 2006 (UTC)

lets use all of them haha they are beautifulthuglas^T|C 20:48, 25 February 2007 (UTC)

Copied

Part of the article has been copied by [1] without respectng GFDL. Cruccone 23:37, 11 November 2006 (UTC)

I don't speak Slovak. Using Babel, I've asked a Wikipedian who does to speak to the author of the website. --Eyrian 23:52, 11 November 2006 (UTC)

Diagram

We need something like [2] [3] [4] [5] — Omegatron 05:35, 2 January 2007 (UTC)

How to section

Can I remove the tag? It's really not a big deal. — Omegatron 05:36, 2 January 2007 (UTC)

Possible vandalism alert

Slashdot recently linked to an article that prominently linked to this page on Wikipedia so keep your eye out for vandals. --froth^{T C} 07:43, 4 January 2007 (UTC)

Clarification needed

This is very confusing to me. First it is stated:

Ferrofluids are composed of nanoscale ferromagnetic particles

Later we read:

Ferrofluids have numerous optical applications due to their refractive properties; that is, each grain, a micromagnet, reflects light

When I link to the micromagnet hyperlink, I am taken to the article on magnets. So the second quote is saying that ferrofluids are composed of particles, each of which is a magnet. That is, each particle exhibits a magnetic moment (I guess is the way you say it) without an external magnetic field being applied. But if that is true, why is the first quote "Ferrofluids are composed of nanoscale ferromagnetic particles" and not "Ferrofluids are composed of nanoscale magnetic particles"? —The preceding unsigned comment was added by 4.238.240.56 (talk) 08:51, 18 February 2007 (UTC).

More correct would be this "Ferrofluids are composed of nanoscale ferro- or ferrimagnetic particles"Abiermans (talk) 21:45, 12 December 2007 (UTC)

History

How/When/Why was Ferrofluid developed and by whom? Answer that question and this will be a better entry --CPQD 00:45, 25 February 2007 (UTC)

Idea

This is just an idea, but someone might want to increase the size of the pictures on the topic page, by a little bit.

Tell me if you want me to do it. --•Tbone55•^{(Talk) (Contribs) (UBX) (autographbook)} 20:44, 25 February 2007 (UTC)

I agree - its a nice image. Id do it but id probably delete wikipedia or something. I nominate you :P thuglas^T|C 20:46, 25 February 2007 (UTC)

What if you Froze a ferrofluid whilst the magnet was present?

Would this make the particles freeze in their new alignment? making the fluid a ferromagnet as long as it was frozen? I'd guess so, cos it would be like the heat and beat method of making iron ferromagnets. Does anyone know for sure? Tom Michael - Mostly Zen (talk) 22:39, 25 February 2007 (UTC)

- Nothing would happen during "normal" freezing. You have to understand that "freezing" is just fixing the particles in place. It does nothing to stabilize the field of the particle. They are so small that they will fluctuate happily even when frozen. Otoh, if your cryostatically freeze them (i.e. going down to Liquid He temperatures), you might get below the superparamagnetic limit of the particles. In that case, they would act as an ferromagnet. 134.105.82.206 11:15, 4 June 2007 (UTC)

If you freeze a ferrofluid all the individual particles will be fixed in space position wise as someone mentioned. 'How' you freeze the ferrofluid is irellevant. There are two ways in which a ferrofluid looses any net magnetization after an applied field is removed. One way is physical rotation of the individual particles, this results in complete randomness and no net field. The other way is rotation of the magnetic moment inside each individual particle. While you can prevent the first mechanism by freezing, you can't stop the second mechanism from taking place, no matter how cold you make it. Also, don't forget that the particles are not touching each other in a (frozen) ferrofluid. A frozen ferrofluid therefor can have a net magnetization but this field will not last if the external field is removed, you can't make a permanent magnet by freezing a ferrofluid in a magnetic field and then turning the external field off. Someone correct me if I am wrong please.Abiermans (talk) 21:58, 12 December 2007 (UTC)

Role of surfactant in a ferrofluid

These surfactants serve to decrease the rate of ferroparticle settling, of which a high rate is an unfavorable characteristic of ferrofluids. The ideal ferrofluid would never settle in the absence of real-world friction. Surfactant-aided prolonged settling is typically achieved in one of two ways. In the case of the addition of soy lecithin, the surfactant particles are nanospheres and prolong the onset of settling via Brownian motion. In the case of oleic acid and other micelle surfactants, the effective diameter of each ferroparticle is increased by the attachment of micelle molecules to each ferroparticle, thereby increasing particle diameter and making fluid remixing (particle redispersion) occur far faster and with less effort.

I think the information above is not correct. Making a stable ferrofluid requires solving of two problems. The first problem is settling of the particles in a magnetic or gravitational field. This problem is solved by making the magnetic particles very small, typically 10nm or smaller so that they can be kept in suspension by Brownian motion. The second problem is clumping together of the magnetic single domain particles, these particles are magnets afterall. That problem is solved by coating the particles with a surfactant. Steric repulsion prevents the particles from agglomorating. The surfactant addition has nothing to do with settling in the way it is described. This should be changed in the article. I am not sure I am comfortable editing the article.Abiermans (talk) 22:21, 12 December 2007 (UTC)

Dear Abiermans, I think you have a valid point about surfactants preventing agglomeration of ferro-particles and so, I think that section should be changed a bit. Before deleting some of the text that emphasized Brownian motion, I considered that a large surface area ball of miceles around a ferroparticle would get bumped around more frequently and this could help to keep the particle in suspension. Or perhaps the impacts would all get averaged out: more impacts but from opposing/self canceling directions? I don't know enough about Brownian motion to know. I considered surfactant action in terms of micels and I thought I understood the whole story, but, I don't understand how nanospheres of soy lecithin could prevent agglomeration of ferroparticles. I made some changes to this section, feel free to re-edit if you think I've missed something.

Best regards, ElectricmicElectricmic (talk) 06:51, 13 December 2007 (UTC)

Hi Electricmic Thanks for the reply, I have taken the liberty of editing the article a bit. I rewrote part of the section on the surfactants and added the fact that ferrofluids contain either ferromagnetic OR ferrimagnetic particles. Let me know if the current version is acceptable.Abiermans (talk) 23:20, 14 December 2007 (UTC)

Hey AbermansWow! That's great. Very clearly stated. The very next paragraph still has a reference to nano-sphere surfactants. "Whether or not the surfactant is nanosphere-based or micelle-based, " I still don't understand the nanoshpere based surfacant's function in maintaining colloidal stability. Also, this sentence is now a bit out of sorts as it references a previous sentence that has been removed. I'd like to delete it but I don't understand the issue enough to be confident that I'd be improving the article. Thanks for your contributions.Electricmic (talk) 07:48, 15 December 2007 (UTC)

Does anyone know how the non polar surfactant tail interacts with the carrier liquid? Is this considered a bond or just a weak attraction? What is the method of attraction between the non polar side of the surfactant and the carrier liquid?Electricmic (talk) 08:04, 15 December 2007 (UTC)

paramagnetism versus superparamagnetism

In fact, ferrofluids display paramagnetism, and are often referred as being "superparamagnetic" due to their large magnetic susceptibility.

Ferrofluids are not referred to as "superparamagnetic" because their magnetic susceptibility is large. They are "superparamagnetic" because they exhibit paramagnetic behavior even when at temperatures below the Curie or the Néel temperature. At least this is my understanding of ferrofluid behavior. —Preceding unsigned comment added by Abiermans (talk • contribs) 23:28, 14 December 2007 (UTC)

The page on paramagnetism makes no reference to super-paramagnetism. It would be great to have it described in the paramagnetism page.Electricmic (talk) 07:53, 15 December 2007 (UTC)

Needs Fix

All nano-particles are sub-microscopic. Someone chnge this please, it's redundant.