[Peter123]

I'm trying to determine what compound, if any, expands once it's temperature reachs around 100 degrees F.

I need somethng that can go in a flexible tube with a hollow core of about 1 inch. There will be a liquid traveling through the core, and I need the compound to expand once the liquid reaches the neighborhood of 100 to 105 degrees so that the flow is interupted. It doesn't have to a 100% closure, some seepage will be acceptable and the pressure in minimal.

Any suggestions would be appreciated.

[Borek]

I would go for a small baloon filled with gas that will expand with temperature. Perhaps a rigid tube with a baloon at one end, to make changes more pronounced.

Most compounds you may think off will behave very similar.

[invisiblegs]

It sounds like you are trying to make a thermostat valve similar to the one in the engine of a car.  The way you are describing it, you seem to want an on/off reaction at a specific temperature.  With your proposed setup, you may look into using a chemical that has a boiling point very close to your cutoff temperature.  This will make it so that the balloon/tube is very small at lower temperatures, but once the liquid inside vaporizes, it will greatly increase in volume.  A common chemical that comes to mind that might work is diethyl ether.  It has a boiling point of 34.6 deg C or 94.3 deg F.  However, if you decide to use ether, be very careful because it is flamable and extremely volatile.

[ARGOS++]

Dear Peter123;

In case of a boiling solvent a little bit more secure option could be:
     Di-Chloro-Methane (DCM)    with Bp:  40°C  =  104°F     or
     n-Pentane                         with Bp:  36°C  =    97°F

At least DCM has a quite narrower (14% - 22%v/v) “Explosion Limit” as Diethyl-Ether (1.7% - 48%v/v) and also a very high “Autoignition Temperature” of  661°C and NO “Flashpoint”.
Flashpoint of Diethyl-Ether = -40°C !!!! and a “Autoignition Temperature” of  170°C

Good Luck!
                    ARGOS⁺⁺