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the color, however, the color alone does not reveal the true nature of such
phases. So mysterious are blue phases, in fact, that scholars had no other ba-
sis on which to name them but to refer to their color. This overly simple name
seems to reveal all the more how confused the researchers involved in the first
understanding of these phases must have been.
Early studies on blue phase were assuredly marked by one astonishing dis-
covery after another, such as the narrow stable temperature range, optical
isotropy, three-dimensional order, and frustration. These unique character-
istics, not observed in any other liquid crystal phases, have enthralled these
pioneering researchers, as is obvious from their writings.
Blue phases, once a subject of academic and basic studies only, are now
attracting the attention of researchers in a range of application-based fields.
These phases, once a headache for many scientists, are in no way easy to
understand, even for the leading engineers of today. This chapter aims to
present, as plainly as possible, the history of study on blue phases, some of
their essential nature, and the recent progress made in the field.
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WhatareBluePhases?
Blue phases are liquid crystal phases that appear between chiral nematic
phases with relatively short helical pitches and isotropic phases. Generally,
blue phases have the following characteristics:
1. Narrow temperature range (typically ca. 1 K);
2. Optical isotropy;
3. Optical activity;
4. There are three kinds of phases, blue phase I (BP I), blue phase II (BP II),
and blue phase III (BP III), in order of increasing temperature.
5. BP I has body-centered cubic symmetry, BP II has simple cubic symmetry,
and BP III has isotropic symmetry.
6. The unit lattices of BPs I and II have a lattice parameter of approximately
200 to 300 nm, with Bragg diffraction in the ultraviolet and visible region.
Understanding of the basic nature of blue phases up to the 1990s was sum-
marized in many distinguished articles [1-6].
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Discovery of Blue Phases
As is well known, Reinitzer and Lehmann discovered liquid crystals some
120 years ago, in 1888. A letter exchanged between these two pioneering re-
searches contained descriptions suggestive of blue phases even at that time.
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