[ioftd]

I am looking for a liquid that needs to have some pretty specific characteristics.  It needs to be clear, have a specific gravity of at least 1.15 to 1.2, have a low surface tension and be relatively safe and non-toxic to be working around.  Right now I am using pure glycerin, but the relatively high surface tension has been a problem. Perhaps a certain sulfactant would reduce the surface tension without changing the other properties of the glycerin?

I am basically using the glycerin to support another liquid and then pulling an object vertically through both liquids. My problem is that the surface tension at the interface between the liquids causes the glycerin to be pulled up into the other liquid, then suddenly that tension will break and the upper liquid will flow back in an uncontrolled way.  I want to eliminate or at least reduce the tension that is causing the glycerin to be pulled upwards along with the object.  Like I said I'm open to some kind of additive to the glycerin or a completely different chemical, but I am introducing this stuff to a studio full of people and lacking most lab safety equipment so it has to be safe and non-volatile.  I've found a few other chemicals that seem to fit the bill but they always seem to be highly corrosive or toxic or flammable.

I have little-to-no background in chemistry or physical science but have been trying to do some research for this project so I may be misusing or misunderstanding some of these concepts and terms, so please correct me if I'm off base.
Thanks!
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[Arkcon]

I don't think its so much the surface tension, at the interface, as much as simply something that a viscous solution will do when pulled through another solution that's less viscous.  By the way, what is the other liquid?  I was going to suggest a sucrose solution, as something you can create with any viscosity and specific gravity you want.  However, you'll want the liquids to not dissolve in each other.

[ioftd]

The liquid that I am trying to float on top is an acrylic monomer.  It doesn't dissolve in water, so water based solutions will work. I have not tried a sucrose solution but I did use a 22% salt water solution and it was actually much worse than the glycerin as far as pulling up into the acrylic resin.  I have been going by the average distance the bottom liquid pulls into the upper liquid before the tension breaks and for the glycerin its 1-2mm while the salt water was 3-5mm.  This is what lead me to believe it was a problem with surface energy.

My latest test is to mix in hand soap to the glycerin and salt water mixtures as a sulfactant, but it takes some time for the solution to become clear after the soap clouds it up, so I haven't yet been able to test it.

Do you think a sucrose solution would be better somehow?  My understanding is that you can mix a denser concentration of sucrose than with salt, as salt water becomes saturated at 25% which may be advantageous.

I have also been looking into using vibration to help break that tension, my first test was taking the rumble motor out of an xbox controller but it doesn't seem to have much effect.  I am looking into ultrasonic vibration, but since ultrasonic is often used to emulsify liquids (which I definitely don't want) I'm hesitant to spend money on that equipment.

Thanks for your help, any direction you or anyone else can give me is greatly appreciated.

[sophotect]

Sodium silicate is inexpensive & readily available at ceramics shops. Specific gravity ~1.25 - 1.4, water soluble.

You could try spraying or injecting a very thin layer of dilute mild acid like vinegar or citric acid on top of the silicate to form a thin, breakable layer of silicic acid that may help protect against flow back from the acrylic layer. I haven't actually tried this but I have played around with silicates & ceramics chemicals a bit, it seems reasonably possible.

Another thing that might work is a polyvinyl alcohol film between layers, which would dissolve in water within minutes. PVA is temperamental though, I have never been able to get above 2% concentration without plenty of work & copious swearing.

I have sunk about 900$ into ultrasonics so far, originally for a ceramic drilling app but its performance was worse than a Dremel.
It does vibrate aqueous liquids somewhat energetically but the horn design & milling is application specific & a significant portion of the cost. The next thing I am going to try it with is vibration of sealed pressurized silicate solutions in an attempt to reduce crystallization times.