Which Liquid Becomes Solid On Heating?

It is possible for a super-cooled liquid to turn solid when it is heated, and polymerisation also involves a process where liquid turns solid on heating, although in this case the process is not reversible.

The only liquid which turns into solid after heating and then returns to a liquid when cooled down again is a solution of 4-methylpyridine, 4MP, water and a-cyclodextrine, aCD.

• Cyclodextrines

Cyclodextrines are so-called cyclic structures containing certain hydroxyl end groups, which are able to form hydrogen bonds either with 4MP or water molecules.

• The process

It is possible to dissolve up to a total of 300g of aCD in one liter of 4MP, resulting in a homogenous, transparent solution. If this solution is then heated to between 40 degrees C, 104 degrees F, and 75 degrees C, 167 degrees F, it turns into a milky-white solid. As the aCD concentration increases, the temperature at which the solution becomes solid decreases.

• Sol-Gel System

Studies have shown that the solid phase of the solution is a so-called sol-gel system. In this system, the creation of hydrogen bonds linking the aCd and 4MP results in an ordered and rigid structure. When the temperature is lowered, these hydrogen bonds break and then reform in the aCD, resulting in the solution reverting back to being a liquid.

• Molecular Dynamics (MD) Simulations

MD simulations have provided confirmation of a distortion of the cyclodextrine ring as the solution is heated close to the temperature of solidification. It appears that the a CD hydrogen bonds break, resulting in the hydroxyl groups rotating outwards, allowing the formation of a network of bonds between different molecules.

Other cyclodextrine and pyridine systems apparently also turn solid on heating and further studies on sol-gel systems are in the process.

Egg yolk

I think every proteineous liquids become solid on heating like Albumen. As far as I know. But let me know if any other is there.

Sea water when we heat it turns into salt....