[p.v.todorov]

Greetings fellow chemists. I have come here seeking help...

I've taken all the chemistry classes my school has to offer, and I've been a teaching assistant for several levels of chemistry classes for a while. This means that I prepare all the laboratory exercises for the classes and make sure things work out. However, I grew bored of the standard labs a few weeks ago. Although they demonstrate chemical concepts very well, there is very little "wow factor" to the standard lab. After I saw a video of ferrofluids in action on YouTube, I decided to make the students synthesize ferrofluids. This would not only cover pertinent concepts such as intermolecular interactions (between the surfactant and iron particles) but also allow the students to see something fascinating and perhaps lead them to have greater interest in science.



I checked out several protocols for synthesis:
http://www.sci-spot.com/Chemistry/liqimag.htm
http://my.fit.edu/~jbrenner/nanotechmanual/Ferrofluids/ferrofluids%20article.pdf
http://www.mrsec.wisc.edu/Edetc/nanolab/ffexp/

I decided to go with sci-spot because I lacked a compound used in the other two (tetramethylammonium hydroxide), however, I've found this protocol to be slightly lacking in description.



Sci-spot's protocol is easy to follow as far as the synthesis of FeCl₂ goes.

The next step after one has an FeCl₂ in HCl is to percipitate the iron as magnetite (Fe₃O₄) using ammonia, leaving this in an ammonium chloride solution. This is where I have trouble as if I use highly concentrated ammonia for this step I create chunks of magnetite (whereas my goal is to make fine magnetite particles). Using low concentrations of ammonia on the other hand produces fine particles (but produces much less magnetite).

The following step here is to surround the magnetite with oleic acid as a surfactant, however, this is done as ammonia is boiled off, and again I've noticed that the ammonia reacts with the oleic acid when it's placed in solution forming white gelatinous blobs (somewhat similar in appearance to the "skin" that whole milk forms after being heated and let cool) . I tend to remove blobs these and keep the remaining oleic acid which tends to form spots in the solution like an oil spill (they're black due to magnetite dissolved within).

The final addition of kerosene I find tends to make a solution that is too dilute (all the pictures I have of ferrofluid show a black substance, whereas mine is brown and slightly transparent). If I let it settle for few days, distinct layers are formed, and I do get a response to a strong magnetic field where the fluid level banks to one side of the beaker, but not spikes.



My questions:
1. Should I use concentrated solutions of ammonia and ferrous chloride to obtain my magnetite? I've noticed that physical agitation of the product in an erlenmeyer flask tends to reduce the particles in size (but would this be enough to reduce their size significantly so that they could be suspended effectively in solution?)
2. Tying into the above question, I've noticed that the oleic acid tends to have no visible magnetite particles in it. Does the initial size not matter as in essence the oleaete ions should surround magnetite molecules individually? (and hence using concentrated solutions wouldn't matter as initial particle size would not be close to the final size)
3. Is the precipitate produced by oleic acid in contact with ammonia normal? The protocol says that this should be ammonium oleate, a slightly soluble soap, but I assume any solids should be dissolved before the addition of kerosene...
4. Have any of you actually followed this protocol or made a ferrofluid previously? Any other comments/suggestions?

[p.v.todorov]

Sorry to have bothered, I figured out my problem today (too viscous and concentrated as opposed to me initially thinking it was not concentrated enough!) Will post more about my synthesis when I've improved the end product as right now I'm getting changes in level and shape that are more round (as opposed to the desired spikes).