Is there any fluid that sinks when heated?
Frank Znidarsic
Doubt it since it would hint at suppressed vibrational modes - OTOH - there
is one candidate that I know of - a complex sugar molecule that turns solid
on heating, and then reverts to liquid on cooling. It is the only one that
does this. However, I do not know if the solid is denser or not. It probably
is not denser, despite the fact most solids are denser, or they would have
mentioned it in the study.
http://www.phschool.com/science/science_news/articles/to_freeze_add_heat.htm
l
There are a few common elements or molecules that are less dense as solids,
and will float on their liquid counterpart:
* gallium - 5.91 (solid) vs 6.095 (liquid)
* bismuth - 9.78 (solid) vs 10.05 (liquid)
* germanium - 5.323 (solid) vs 5.60 (liquid)
* silicon - 2.3290 (solid) vs 2.57 (liquid)
* water - 0.917 (solid) vs 0.998 (liquid)
>From the study above: "We report a reversible liquid-solid transition upon
heating of a simple solution composed of a-cyclodextrine (alpha-CD), water,
and 4-methylpyridine. These solutions are homogeneous and transparent at
ambient temperature and solidify when heated to temperatures between 45° and
75°. Quasielastic and elastic neutron scattering show that molecular motions
are slowed down in the solid and that crystalline order is established. The
solution "freezes on heating." This process is fully reversible, on cooling
the solid melts. A rearrangement of hydrogen bonds is postulated to be
responsible for the observed phenomenon."<<attachment: winmail.dat>>
