# Talk:Ferrofluid

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## Major revisions needed

This page is need of some heavy editing since it contains a lot of errors. I was about to start, when I realized it was more work than I asked for. The structure of the article is quite bad and there is a lot of duplicate sentences and plain fact errors. Also most of the chemistry in the article is way off. Hematite is an antiferromagnetic phase and can not be used to form ferrofluids. The physics and chemistry of ferrofluids and magnetorheological fluids are a firmly established research fields and ferrofluids deserves a decent wikipedia entry. I will try to do what I can to tidy up/edit this page in the coming weeks and add some of the great references in on the topic astrolux (talk) 19:40, 5 July 2010 (UTC) —Preceding unsigned comment added by Astrolux (talkcontribs) 19:36, 5 July 2010 (UTC)

## CSI: NY

I watched the 4th season's 15th episode "DOA for a Day". in the episode, ferrofluid is identified because it is "sensitive to sound". While I strongly beleive this is inaccurate, can anyone specifically discount this. —Preceding unsigned comment added by 65.101.183.104 (talk) 01:39, 20 October 2008 (UTC)

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)

Actually a ferrofluids viscosity does change under the influence of a magnetic field. It is easy to see why. At zero field the particles are free to move as they like. When a magnetic field is applied this is no longer the case since the particles are forced to align in a specific direction. The stronger the field, the less free the particles are to freely move, which translates to a viscosity change.Abiermans (talk) 10:04, 19 December 2007 (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)

Also, ferrofluids DOES damp the electric coil in a loudspeaker in a way, so that unwanted resonances taking place in that coil are damped. It translates into overall improvement of the sound quality. References : http://mrsec.wisc.edu/Edetc/background/ferrofluid/index.html http://www.popsci.com/diy/article/2009-09/making-ferrofluids-work-you - Narayanarora —Preceding undated comment added 10:08, 6 January 2012 (UTC).

## 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 beautifulthuglasT|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. --⁪frothT 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

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)

This may answer your optical applications questions: http://www.nanomagnetics.us - Look at the image gallery and John Shearers microscope images from the research link.Pinestone —Preceding unsigned comment added by Pinestone (talkcontribs) 12:01, 11 March 2008 (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. --(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 thuglasT|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)

Hi Electricmic Well, the surfactants are nanoscale particles but I don't think there are nano-sphere surfactants because you need a polar(non polar) head and non-polar(polar) tail construction. Not entirely sure how to accomplisch that when you have a sphere.Abiermans (talk) 19:05, 17 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)

My first guess would be that these interactions are governed by van der Waals forces.Abiermans (talk) 19:05, 17 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 (talkcontribs) 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)

I guess it would be handy to add a link in the text mentioning superparamagnetism. Although it is present on the page way on the bottom?Abiermans (talk) 18:57, 17 December 2007 (UTC)

I rewrote the paramagnetism page but I am not quite sure how to include this. I think there is a big problem in nomenclature here. Maybe the macroscopic response of a ferrofluid can be called (super)paramagnetic, but can the material be called that? Surely within each single domain the thing is ferromagnetically ordered! I think the statement ferrofluids display paramagnetism is incorrect. Ferrofluids display superparamagnetism and then explain that the latter requires ferro-ordering at the domain level, I'd think.

Jcwf (talk) 01:14, 1 January 2008 (UTC)

## Needs Fix

All nano-particles are sub-microscopic. Someone chnge this please, it's redundant. —Preceding unsigned comment added by 24.86.253.202 (talk) 20:21, 15 December 2007 (UTC)

I removed the term sub-microscopic.Abiermans (talk) 19:06, 17 December 2007 (UTC)

## the shape and nature

someone explain why this occurrence is so......uniform in appearance please. —Preceding unsigned comment added by Murakumo-Elite (talkcontribs) 08:29, 29 January 2008 (UTC)

From what little I know, the peculiar shapes are caused by the liquid's reaction to the magnetic field lines. 71.113.22.132 (talk) 06:21, 2 March 2008 (UTC)

## Human Reaction

I think a small section should be added to describe the result of human consumption or physical contact with ferrofluid. 70.190.40.163 (talk) 04:57, 22 July 2008 (UTC)

Yeah, it's good idea (I can't write about it because I don't know reactions of human body for psychical contact with this amazing substance as is ferrofluid)
83.23.204.72 (talk) 21:06, 21 October 2008 (UTC)
I reverted your template asking for "psychical"[sic] reactions. It's enough to request it here on the talk page... no need to slap an ugly tag at the top of the article. Binksternet (talk) 23:01, 21 October 2008 (UTC)

## Surfactants again

Oleic acid does not usually act as a surfactant unless it is saponified. So is oleic acid correct, or should it read "saponified oleic acid?" Rees11 (talk) 16:23, 22 March 2009 (UTC)

## Please note: incorrect reference

Magnetic viewing film is NOT in any way related to ferrofluid, and the reference should be removed. "It is a translucent thin flexible sheet, coated with micro-capsules containing nickel flakes suspended in oil" Nickel flakes are not nano-scale matter and is misleading and confusing for the reader.~~Pinestone 10:48, Sept 24, 2009 (EST)~~

You seem to have misunderstood the purpose of See also sections: They're purely for navigation purposes, not content. Readers of this article might reasonably be expected to have an interest in reading one or more of the articles listed there; therefore, someone listed the article in See also. No direct connection is implied or expected as a result. WhatamIdoing (talk) 03:41, 30 September 2009 (UTC)
If you want to adjust a disputed point in an article, an assertion is not sufficient. Please provide references to substantiate your point. WLU (t) (c) Wikipedia's rules:simple/complex 10:26, 30 September 2009 (UTC)

## Curie temp

The sentence below sounded wrong to me so I will change it. Shouldn't the Curie temperature of a ferrofluid be independent of the carrier liquid and surfactant?

"However, ferrofluids lose their magnetic properties at sufficiently high temperatures, known as the curie temperature. The specific temperature required varies depending on the specific compounds used for the nano-particles, surfactant, and carrier fluid." Electricmic (talk) 05:06, 22 October 2009 (UTC)

## Brownian Motion

I think Brownian Motion is a red-herring in this discussion. Even if there were no such thing as Brownian Motion the steric repulsion of the micels would keep the nanoparticles in suspension. Also, a strong magnet pulls the magnetite with forces far greater than the gravitational weight of each particle. "Weight" is another red-herringin this discussion. Who will word-smith a better paragraph than what we currently have (below)? "These surfactants prevent the nanoparticles from clumping together, ensuring that the particles do not form aggregates that become too heavy to be held in suspension by Brownian motion. The magnetic particles in an ideal ferrofluid do not settle out, even when exposed to a strong magnetic, or gravitational field." Electricmic (talk) 13:10, 22 October 2009 (UTC)

## Jennifer's Body

It was in the movie Jennifer's Body (2009), when Jennifer just became a daemon and vomited a blacky 'evil'. —Preceding unsigned comment added by 151.72.35.57 (talk) 09:10, 30 January 2011 (UTC)

Are you claiming that this is a reference to ferro-fluids in modern culture or something? (Ferrofluids are often black and move oddly in the presence of magnetic fields). I kinda doubt it - and it certainly doesn't rise to the level of needing to be mentioned in this article. SteveBaker (talk) 14:58, 30 January 2011 (UTC)

## History Section

Could someone please add a History Section to this article, better explaining the HISTORY of Ferrofluid? Thanks! Don't forget the sources. — Preceding unsigned comment added by Doubledragons (talkcontribs) 17:58, 9 March 2012 (UTC)

Some (admittedly brief) investigating only yields that ferrofluid was "discovered in the 1960s at the NASA Research Center, where scientists were investigating different possible methods of controlling liquids in space." I can't find the names of any researchers involved, any records of the experiment(s), the exact year, or anything else. This small amount of information seems difficult to incorporate into the article without more details. MosmordeanCreed (talk) 03:09, 8 May 2013 (UTC)

## Removing equation on resistance of a ferrofluid

I am going to remove the equation on the resistance of a ferrofluid. For your reference, the equation as it is currently is shown below:

Ferrofluids also change their resistance according to the following equation[citation needed]:

$\rho = Ve^{-B^{2}} + p$

With:

• $\rho$ as the resistance in M$\Omega$
• V as the Vollema Value, different for each ferrofluid,
• B as the strength of the magnetic field in mT,
• p as the Pietrow constant, currently measured at 0.09912
—Ferrofluids Wikipedia Article 25 April 2014 , https://en.wikipedia.org/wiki/Ferrofluid

There are a lot of problems with this formula. Most pressing is that I can't find a legitimate scientific reference for an equation for the resistance (or probably more accurately the resistivity) of a ferrofluid, and I can find no data on the Vollema Value or Pietrow constant that isn't clearly copied word-for-word from this article.

Another issue is that this equation is extremely poorly mathematically expressed. The argument of an exponential should be dimensionless, yet in this formula it clearly has dimensions of mT^2. The Vollema Value is very undefined, though I assume it is a value in mega-ohms. However, the Pietrow constant as far as can be identified from the article, appears to be a dimensionless number, which is nonsense! You can't add two dimensionless numbers (or mega-ohms and a dimensionless number) and get mega-ohms!

Because all these issues with this formula are so egregious, and since it appears that this formula has already been blindly propagated to other sources on the web and has been misleading high school students: http://www.slideshare.net/sunjerry019/ferrofluid-v2-9117602, http://www.thescienceforum.com/physics/25051-vollema-value.html, I am going to delete it. If someone finds it necessary to re-introduce this formula (cleaned up), they can use the quotation above as a reference. Tevye guy (talk) 10:04, 25 April 2014 (UTC)