heated this sample of a liquid crystal called PCH past 70 °C, the molecules
changed from a liquid crystalline phase, in which they assembled into a series
of ordered helices, to a so-called isotropic liquid phase that has little
molecular order. The twist in each helix is imparted by a small amount of the
chiral molecule pregnenolone. As the helices effectively melted and unraveled in
the increasingly high temperatures, the liquid changed its shape and appearance
as seen here. Vance Williams’s group at Simon Fraser University used optical
microscopy (at 10× magnification) and cross-polarized light conditions to study
this sample of chiral liquid crystals, which can be used in thermometers and
even mood rings. Because the pregnenolone molecules are chiral and
enantiomerically pure, cross-polarized light creates a range of colors when it
shines through the sample.
The disappearing spoon, a classic magic trick, takes advantage of a
basic physical property of the element gallium: The pure metal melts at 29.7 °C.
For the trick, an illusionist casts a spoon from gallium, an easy feat on a
stovetop. The spoon looks, sounds, and feels like a normal metal spoon at room
temperature. But when stirring hot tea or water at just under 100 °C, the spoon
quickly melts and pools at the bottom of the glass. Performers often use a
special cup with a hidden chamber at the bottom; the now-liquid gallium flows
out of sight of the audience, completing the illusion.
Gallium is available to the general public from a wide range of online