[Char]

Hello,

I am working with dissolving styrofoam with acetone and Ive come across a problem where I need to dilute the acetone somehow to slow the dissolving process.
After researching I thought that water would dilute the acetone just fine, but after trying it out I found that even adding the smallest bit of water to acetone slows dissolving the polystyrene dramatically.
After doing research for days (I am not educated in chemistry at all) that it has to do with the hydrogen bonds between water and acetone.

Is there another way I can dissolve styrofoam as an art student with a limited budget? Or is there anything I can mix in the acetone to dilute it that would hold the properties that dissolve polystyrene?

Thanks so much for reading. This is a creative endeavor so any ideas are appreciated. 

[Enthalpy]

Hi Char, welcome here!

True, the dissolution of styrofoam is impressively quick. I've never tried to slow it down, but you could try other common solvents, since styrofoam dissolves rather easily. Do I remember that trichloroethylene works and is as quick as acetone? You might try turpentine, white spirit, toluene or xylene, etc.

Please be careful with solvents. Many are quite volatile, so they catch fire easily, and accumulated vapours can explode - especially ether, acetone, methanol, ethanol. Some are also less than healthy, acting as narcotics or worse; at least once I saw an allergy to acetone vapour, it was impressive. In a public show this would be a worry.

Other ketones are available as solvents beyond the common acetone (=dimethylketone): ethylmethylketone, methyl isobutyl ketone, diisobutyl ketone (doesn't burn easily)
http://www.shell.com/global/products-services/solutions-for-businesses/chemicals/products/solvents/chemical-solvents/ketones.html?gclid=CIPVp-COr8gCFYrpwgodpiMJGw

[Intanjir]

I once had the opposite problem. I wasn't getting good enough dissolution of polystyrene in acetone, there was always this cloudy gelatinous goop in the center. I recall a mixture of similar parts acetone and toluene was a much more effective solvent for styrofoam than acetone alone, letting me fully dissolve it. After the solvent had dried I was left with a nice semi-transparent plug of solid polystyrene at the bottom of the beaker.

If you are interested in the theory, I used Hansen solubility parameters to figure out what mixture of solvents to try.
This pdf has many of the relevant numbers for predicting what mixtures of a couple solvents would be better or worse solvents for polystyrene.

The other ketones seem to generally have parameters closer to the parameters for polystyrene than acetone does, suggesting they may be even better solvents for polystyrene than acetone. However they will also all be larger molecules than acetone is and size can definitely slow things down even if you eventually end up dissolving more.

The problem with adding water to acetone is that it greatly increases the hydrogen bonding parameter δh and at the same time also increases the polar bonding parameter δp both of which move us away further from the parameters for polystyrene. What else might you add to acetone to move away from polystyrene that wouldn't be so dramatic?