the students that you have demonstrated how to see the colors in
white light through diffraction and polarized transmission. Making
sure that everyone is looking at you, take the large
sheet of microencapsulated liquid crystal and place it
against your face, shiny side out. [If you wear glasses, remove
a bit for the oohs and ahs to die out,
then ask... Where do the colors come from? [If
some students say the heat from your face, answer no.]
that the colors come from the white room lights reflecting off
the black paper.
the teacher passes out the Magic Patch Theme Packets, explain
that the paper has liquid crystal fluid trapped, or encapsulated,
against the shiny side. [Note: The large
demo sheet and the give-away patches are not made from the same
liquid crystal material. The patch material goes through a complete
color change with a temperature change of 71° F to73°
F. If the room is warm, you may have to open the ice pack to enable
students to cool their patches down. Ice cubes also work well.]
that each student determine if she (he) is a vampire by placing
the magic patch on the inside of her (his) wrist. [Vampires
are the living dead and give off no heat.]
if anyone can see a vein. [This
would be characterized by a blue line.] To explain selective
reflection in liquid crystals and mood rings, you
may use the set of transparencies included as follows:
Crystals in Education Transparency
are laying on the grass, disguised as liquid crystal mole cules.
In liquid crystals, the molecules show a high degree of organization
and alignment in some regular order.
Reflection in Cholesteric Liquid Crystals Transparency
we try to stack students (or liquid crystal molecules) in a series
of layers on top of each other, they tend to twist as shown on
the left of this picture. The heads of the students point in a
spiral direction as we move up through the structure, like a spring.
of the liquid crystals in the black sheet as springs. When they
are cool, the springs are relaxed with a long pitch (or twist
). [Refer to the lower right hand side of
of the colors in white light pass right through the cool liquid
crystal film and are absorbed in the black paper. The patch appears
body temperature heats up the patch, the liquid crystal springs
get tighter and they selectively reflect the red light
part of the white room lights. As the temperature climbs, yellow,
then green, and final- ly blue light is reflected. This is as
tight as this liquid crystal gets.
effect is reversible. Students may put their patches on an ice
cube or under a mug of hot cocoa to see the effect of selective
reflec- tion. Give a warning that the sheet should not be folded
or marked with a sharp object like a pencil.
Subtle Message About Smoking Transparency
that doctors may study circulation in the body with liquid crystals.
On the left side of the picture, the blue color of the man's hand
shows good blood circulation to the fingers. The picture on the
right side shows that, after smoking one cigarette, the man's fingers
reflect green because of reduced circulation. Nicotine constricts
the blood vessels.
by reminding the students that liquid crystals are found in every
thing from cell phones to watches to laptop computers to GameBoys.
What would the information age be like without the engineers and
scientists who developed liquid crystals?
by Stephen D. Jacobs, Rebecca L. Coppens and Christine Andrews-Angelo
December 24, 2001
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