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Liquid Crystals: A Bridge Between Science and Technology As volunteers for ALCOM Education Outreach, the education program of the National Science Foundation's Science and Technology Center for Advanced Liquid Crystalline Optical Materials (ALCOM), we take advantage of the spectacular optical and electrooptical properties of liquid crystals to teach basic principles of optics to students from kindergarten to beginning college. Normally, students are taught predominantly about the three phases of matter—solid, liquid, and gas—but plasma and liquid crystals are often overlooked or omitted entirely. Some students are already aware of the existence of liquid crystals because they are familiar with the acronym LCD (liquid crystal display) which they associate with computer games, laptop computers, small televisions, and appliances that use LCDs to display information. Our science education program uses LCDs to teach basic scientific principles and to demonstrate the bond between science and technology. Understanding the underlying physical principles of the LCD requires basic concepts from physics, chemistry, and engineering, so liquid crystals are ideal materials to show the link between the various scientific disciplines. The main components of our program include hands-on workshops for students, four-week summer workshops for high school • i> n- • teachers, and a newsletter that i ~ •.11 li il uted to physics educators (pred nily high school physics teacher • n.r.h -n wide. For the students, perhaps iln .!••• I exciting part of the program is t! ••' • I •• • i •• • to fabricate their own LCDs froi 11 -• •.•!• I• The twisted nematic display nn>-l . ••mmonly used in digital wristwai •!•••• 11 culators, and small electronic •!•• i-• incorporates two polarizers, tw-- [•••• i il ly treated conducting glass sul* ii.ilr i nematic liquid crystal, spacers '•• »-••••-»l the thickness of the display, ami • | glue. The students construct llu n ••••• n displays with a little guidance ••inI ••im "subliminal" messages of basic -11111111 importance. They can then test I In 11 •': • plays, applying an electric field to see if a
MRS BULLETIN/JUNE 1994
display switches from transparent to black and observing the transmission of a flashlight (or laser) shining through the cell. The students also demonstrate the rotation of polarization of light; by heating their display into the liquid phase and viewing it between crossed polarizers as it cools to the liquid crystal phase, they can optically observe a phase transition. Many students relate the concept of polarization to their sunglasses. The next display the students construct, known as the polymer-dispersed liquid crystal display (PDLC), operates on the principle of electrically controlled light scattering. Micrometer-sized liquid crystal droplets are dispersed in a polymer matrix sandwiched between conducting glass plates. The PDLC display switches from opaque white to crystal
At the conduslwtf the workshops, the students get down and any 10 motto the long, thm nature of most Hquki
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