Everybody learns in elementary science class that when you take a solid, and continuously apply increasing heat, it will eventually melt into a liquid, and then evaporate into a gas. When you cool said gas, it will condense into a liquid, followed by hardening into a solid. Simple.
But
researchers in France have found a liquid which has little respect for the "laws" (more aptly "suggestions") of physics. When this organic liquid solution is heated to temperatures ranging from 45 to 75 degrees C, it solidifies. When allowed to cool, it melts again.
The cause lies in the molecules' reaction to the increased energy... the hydrogen bonds, which tend to break and re-form easily at room temperature, become stronger when heat energy is applied... the stronger bonds then form a structure, and a solid results. Removing the heat energy weakens the hydrogen bonds again, and it "melts" back into a liquid.
It sounds like the "solid" form is gel-like in consistency, which may limit the useful applications of this material, but it's still spiffy.