[ttlsksky]

Hello~ I am a media art artists working in Korea. (http://illustboy.com)
Recently, create a kinetic artwork using ferrofluid.
I need to create an artificial pond with a diameter of 3 meters. So I need a lot of suspension liquid.

<Prototyping and simulation videos>
https://youtu.be/3o33upltO34
https://youtu.be/NE19B_2byGA

Unfortunately, I tried my solution failed.
- case 1: Deionized water 40% / isopropyl alcohol 40% / Propylene Glycol 20% (Stains occur on the glass )
- case 2: Deionized water 60% / Coco betaine surfactants 40% ( no stain but, This seems strange movements)
- case 3: Deionized water 35% / isopropyl alcohol 35% / Coco betaine surfactants 30% (Stains occur on the glass )
- case 4: Deionized water 60% / LES surfactants 40% ( no stain but, This seems strange movements.)
- case 5: Deionized water 60% / APG surfactants 40% ( no stain but, Decomposed into many particles)
- case 6: Windex(Glass Cleaner) 100%  ( no stain but, Decomposed into many particles)

I used glass types
- pyrex glass (Small stains occur)
- tempered glass (Small stains occur)
- soda-lime glass (Big stains occur)

I was always cleaning solution into a container before adding the alcohol.

And most it had hardened over time, the ferrofluid.

oh.. too difficult...
Please help me.

[Intanjir]

What ferrofluid are you using? Is it EFH-1?

I would guess that a stain is what happens when a thin film of your oil based ferrofluid is stuck to the surface.

I think what you want is for the ferrofluid to be immiscible with the carrier and yet for it to have significantly higher affinity for the carrier than for the glass. Yet at the same time you don't want it to have too much affinity for the carrier or else it will easily form tiny droplets rather than prefer sticking to itself. This seems like a somewhat tricky problem.

It is possible that some ideal concentrations of some surfactants might work, but I wouldn't know which. The main issue with surfactants is they will likely be active on both the glass-ferrofluid interface and the carrier-ferrofluid interface. So to some extent they will compromise the ferrofluid's aversion to the glass.

Besides surfactants you might try different liquids. You tried a mix of water, isopropyl alcohol, and propylene glycol and that still incurred stains. This is still a fairly hydrophilic liquid. PG is very hydrophilic so it may not be of much use. Have you tried just starting with mostly isopropyl and adding water until it stops making small particles? Or try the reverse, starting with mostly water and adding isopropyl until it starts making excessively small particles.

Now you listed surfactants that you tried and they all had large percentages next to them. I can only assume then that you used some kind of solution of the surfactant, though this tells us nothing about how much surfactant and what solvent it was dissolved in. Still the numbers seem very high, I suspect you may have success with the surfactants that left no stains but made for tiny particles if you just use less of them. Just dilute with water until you stop getting small particles and then see if you have staining.

There are other things to try as well. I know it is possible to destabilize small bubbles in foams by adding an antifoaming agent. I would imagine there is something similar to destabilize oil droplets in water but I don't know what such an additive would be called.   
You can also make the glass more hydrophilic. You may not be successfully totally cleaning the glass of oil residue. A high pH detergent like Ajax is good for saponifying residual oil. However you can do better than simply cleaning the glass if you also hydroxylate the surface. Unfortunately I don't know of an easy way to do this. The best you can do without an autoclave is probably to simply boil an alkaline solution in the glass, but I am not sure how effective this would be without pressure. Hydroxylating glass can also be done with very caustic piranha solutions but handling those is probably better left to professionals.

[ttlsksky]

Thank you so much Intanjir!
I need to find a solution mostly hydrophilic you said.
And the need to find a way to more strongly than the glass cleaning.
This was really helpful. I will soon post the results.

[Intanjir]

Adding water to mineral oil + isopropyl results in a very cloudy suspension that will not settle. What is probably happening is the small amount of mineral oil which dissolves in the isopropyl is forced out of solution as the water makes it too hydrophilic. The dissolved oil comes out as very nice dispersion of tiny particles. This is avoided if instead isopropyl is added to water + mineral oil. Nevertheless, instead of cloudiness the aqueous phase exhibits some Tyndall effect suggesting that it contains some nano-sized droplets of oil. I don't have any ferrofluid so I used mineral oil as a proxy. Ferrofluid is opaque so the nano-emulsion may have a more apparent effect. 

[ttlsksky]

I want to give a very big thank you, it is my not enough English language skills. Sorry.
Perhaps, is if mix alcohol with water, shake strongly different results?
I did not cloudy mixture.

Recently I've washed the glass with a purchase cleaner had good results.
https://youtu.be/6NMt5Cz1xWA
Mixing rate was 50% deionized water, 50% isopropyl alcohol.
Glass used a glass of good quality.

But it seems to go a little bit hardened over time, the ferrofluid. And
The mixture turned yellowish. (Oil degradation?)
In practice to use a different method the glass is unstable.

<The main ingredients of cleaner>
Anionic water, Hydroxides (sodium + potassium)

[Intanjir]

You never told is what kind of ferrofluid you have. Did you make it yourself? Is it purchased from some company?

You might try thinning it out a bit with some mineral oil to improve fluidity.

Whatever carrier oil the ferrofluid is in ought to be unreactive, unless some natural oil was used.
The yellow color could be from iron dissolving or suspending in the water. Adjusting the pH to be slightly alkaline 9.5ish would prevent dissolution.
If instead some of the iron is leaving the oil and suspending in the water then you may have to find a different ferrofluid.

Alternatively it may be that the ferrofluid is suspending in the water. If you dilute a bit of ferrofluid with a clear oil does it go from black to yellow?
I'm not immediately sure what you would do to combat a tendency for nanodroplets of oil to suspend other than to try a different solvent.

[ttlsksky]

I used this product.
But I do not know whether this is the type of EFH1 ferrotec company.

I saw a detailed description of the page contents were different from the ferrofluid used in the display cell(https://www.amazon.com/gp/product/B008MB1ROC/ref=s9_dcbhz_bw_d0_g328_i1_sh).

So this seems likely that other additional or other components in addition to the base liquid ferrofluid.