Is there any substance that get more pliable the colder it gets?
I think it would be possible to construct an object or material that gets more rigid as it is heated, but the idea that I have is purely mechanical; it would be a sort of chain affair where the links tighten up due to thermal expansion.
It might even be possible to realise this in some form of polymer or something.
There’s a reason things are generally more pliable when they’re hot. The molecular vibration associated with heat also facilitates molecules rearranging themselves to accomodate some new position and therefore not pushing back as hard.
But I think the alloy “Stellite”, which is used to make metal cutting tools such as the sharp tool on a lathe, gets somewhat harder at a few hundred degrees than at room temperature. I gather this is quite unusual, but not sure.
If something did get more rigid with heat, it would be a parabolic (or similar) affair: It would get more rigid for a while as the heat increased, but eventually it would become progressively less rigid as it began to melt.
Heat eventually destroys every structure. Even atoms turn into ions as electrons are dissociated.
In this connection, sulphur has interesting behaviour: it’s solid at room temperature; very fluid on melting (especially around 140C); then at 155C (when the ring-shaped molecules break and become strings) the liquid gets much more viscous again.
raygirvan, Thats a pretty neat trick.
For what it’s worth, there are many substances that get more solid as they heat up, but in a non-reversible way. Egg whites are an example. And, as Derleth said, keep raising the temp and anything will break down.
Another very good example of this type of behavior are shape memory alloys (SMA). The main commercial variety of SMA is a nickel-titanium alloy, often called NiTiNOL (NIckel-TItanium-Naval Ordnance Lab). SMAs have a transition temperature where the molecular structure changes. Above the transition temperature, NiTiNOL (for example) is in an austenitic phase, where the molecular crystal lattice is in a standard cubic configuration. Below the transition temperature, NiTiNOL is in a martensitic phase, where the crystal lattice forms alternating bands where crystal cells are tilted in alternating directions. Think of the following digram as a crystal latice, with molecules at the junctions of the lines:
Austenitic Martensitic
(hi-temp) (low-temp)
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When the martensitic structure is stressed, the “slanted” crystals actually flip orientation, leading to a a number of neat properties of the material. One such property is (since less stress is required to flip the lattice than to permanently deform it) that the low-temp martensite is less stiff than the hi-temp austenite.
All sorts of NiTiNOL info at SMA Inc. Note particularly that the Young’s modulus (a measure of stiffness) in the martensite is about half that in the austenite. Note that this is not a continuous change in stiffness across temperature, but rather a single jump associated with a change in the crystal structure of the material. Many materials change crystal structure at elevated temperatures (steel for example), so it’s possible that other materials might exhibit a jump in stiffness when heated past a certain point, although few will be as extreme as NiTiNOL.
(First question I’ve answered that relates, albeit indirectly, to my dissertation. Thanks, weeks!)