1999 Summer Research Program for High School Juniors at the University of Rochester's Laboratory for Laser Energetics Page: 10 of 156
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Liquid crystals
The liquid crystalline phase is a unique mesophase in some compounds that is
between the solid. crvstaline phase and the liquid. fluid phase. These compounds possess
a unique "double melting point"-the first melting point is the transition between the
solid. crystalline phase and the liquid crystalline phase. The second melting point is the
phase transition between the liquid crystalline phase and the isotropic (or disordered
liquid) phase.
Liquid crystals have a crystalline structure like a solid, but they move as a fluid.
Liquid crystals have four different "phases"-nematic, cholesteric, smectic, and discotic.
The nematic and cholesteric phases are the primary concerns in this paper. The nematic
phase is the least ordered liquid crystalline phase. The cigar-shaped molecules only are
oriented in one plane. with their long axes parallel. In the cholesteric phase (or chiral
nematic phase) the cigar-shaped molecules are oriented along two planes; the molecules
are arranged in a planar manner in several layers, and the layers are arranged on a helical
axis (Fig. 1).
Fig. 1. Nematic liquid crystals. which are cigar shaped molecules, are oriented along one plane
(above, left). Cholesteric liquid crystals are also cigar-shaped molecules; however, they
are oriented along two planes-the molecules are aligned along their long axes, but the
different layers are arranged in a helical fashion.4
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1999 Summer Research Program for High School Juniors at the University of Rochester's Laboratory for Laser Energetics, report, October 9, 2002; Rochester, New York. (https://digital.library.unt.edu/ark:/67531/metadc715136/m1/10/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.