[Gipo]

Hi guys, this is my first post here, and sorry if my heading does not explain more, but I will try to clarify here.

I am looking for a substance that is non-corrosive, non-toxic(to humans) has a fluid-like constancy (similar to cooking oil) and will expand upon application of heat to at least 50% of it's original state. I would require it to expand once the substance is in direct contact with the human body (imagine it's in a balloon and the balloon swells if you held it in your hands too long)
I don't know if this is a tall order or not, just hoping that there might be an answer to this riddle that has been plaguing me for years now.

[ATMyller]

Paraffin would work rather well, if the temperature range is wide enough for reaching such high thermal expansion.

[Dan]

So you need something that will expand by at least 50% when warmed in your hand? Paraffin will definitely not do that.

I'm not sure this is possible over such a small temperature range. I was thinking about a liquid that boils at around 30°C (e.g. isopentane), but even then as it expands the pressure build up in whatever it is contained in will quickly condense it if you are stretching the walls of the container (e.g. balloon). Also, I'm not sure isopentane is compatible with many rubbers/plastics...

[fledarmus]

For liquids and solids, the volume doesn't change very much with changes in temperature. Even gases aren't going to change by 50% for a, what, maybe 10°C change in temperature?

I'm thinking along Dan's lines - you are probably looking at a phase change, most likely from liquid to gas. Look for a liquid that has a boiling point somewhere between 25°C (approx room temp) and 37°C (approx body temp).

[curiouscat]

I'm thinking along Dan's lines - you are probably looking at a phase change, most likely from liquid to gas. Look for a liquid that has a boiling point somewhere between 25°C (approx room temp) and 37°C (approx body temp).

Might Methyl Formate work?

Alternatively, one of these (but they seem more icky to handle)

Diethyl Ether
1,4 Pentadiene
Methyl IsoPropyl Ether

The pressure could be kept constant via a piston-like arrangement. Not sure if it is practical.

[Gipo]

Ah, I didn't think it would be that easy. well, maybe forget the 50%, I suppose that was aiming too high. I think the better question would be what substance and how much expansion could i get maximum. I could probably work with any type of expansion, although the smaller the amount, the harder my job will be. I definitely do not want a phase change, I want it to remain liquid and pressurize against the walls of it's container ( imagine a balloon in a mesh frame, and when holding it in your hands, the balloon pushes out to the frames to fill the entire space) I suppose the question is now how big the frame will be. Anything under 10% is going to make my job almost impossible, and i'd take anything over that, even by a fraction 
I sort of want it to stop expanding around 40c so a small reaction from small temp range would be ideal.
Again, I know I ask alot, sorry I don't know more about these types of things   

[curiouscat]

Can you elaborate more about the application?

I am confused as to why you are ruling out phase change. It sounds ideal for your baloon in a mesh sort of application. The expansion pre BP would be very small; at BP huge and then again quite small. At the BP a 100% volume expansion should be easy.

You can get it to expand at a pretty precise temp. or even over a range of temp. if you use a mixture. Doesn't matter if it is liquid or gas they both exert pressure on your balloon walls. Worst case add some inert gas if you want your balloon to feel gas-like pre-expansion.

[fledarmus]

10% is possible - the liquids that are used in thermometers have approximately that range of density change. See for example the table labeled "Density of Ethanol at Various Temperatures" on this page - http://en.wikipedia.org/wiki/Ethanol_(data_page). Toluene is another compound that has been used, but it appears to show less change. The density-temperature tables are presented here http://www.springerlink.com/content/3k86716173817l8n/. Isoamyl acetate and kerosene have also been used in thermometers.