Chemistry Reference
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As a cholesteric compound slowly cools from the isotropic phase, blue scat-
tering can be seen momentarily immediately prior to the phase transition to
the chiral nematic (cholesteric) phase. One of the discoverers of liquid crys-
tals, Reinitzer, did not miss this extremely subtle phenomenon [7]. However,
it took another 80 years before blue phases were recognized by the academic
world as specific liquid crystal phases. Although this long delay may have
arisen because the initial discovery was ahead of its time, the lag also re-
veals how these phases were ignored for many years. Not even a single paper
on blue phases can be found for the 34 years from 1922 to 1956. Two ma-
jor reasons for why these phases failed to catch the attention of researchers
is that the phases did not exhibit birefringence, a most typical characteris-
tic of liquid crystals, and that the stable temperature range was extremely
narrow (typically ca. 1 K). For over 80 years, and even though the unusual
phenomenon of blue phases was occasionally encountered by researchers, the
observation was ascribed to a metastable state of the chiral nematic phase,
and further investigation of the phase's true nature was never pursued.
Then, between 1970 and 1990, this misunderstanding was resolved, and
the study of blue phases abruptly became popular, particularly in the field
of physics, leading to the discovery of frustrated phases, one of the most re-
markable events in the entire history of materials science. Now, it must not
be forgotten that one factor leading to this great discovery was the develop-
ment of liquid crystal chemistry in the 1950s. While industrial applications of
liquid crystals were not predicted back then, the foundations of the synthetic
chemistry of liquid crystals had been laid. George William Gray, a British
chemist, was one of the builders of this foundation. He conducted systematic
studies of the phase transition of cholesteric compounds and discovered that
the strange phenomenon of the blue phase, as witnessed by Reinitzer, com-
monly takes place in many of the cholesteric compounds [8]. Then, in 1969,
Saupe made the most foresighted proposal in the history of blue phase stud-
ies [9]. He focused on the empirically discovered fact that the state of this
phenomenon is optically isotropic while having unusually strong optical ac-
tivity, and thus proposed an innovative model of a huge cubic crystal formed
by the three-dimensional expansion of a twisted structure of chiral molecules.
This model, although ultimately found erroneous in certain details, provided
a largely accurate description of the true nature of blue phases. The model
suggested a state in which three-dimensional order exists between a chiral ne-
matic phase with one-dimensional order and a disordered isotropic phase.
It can be easily imagined that such a hypothesis was very bold in Saupe's
time. It is thus admirable that Saupe had this profound insight in the days
when blue phases were still in the dark and the very name, “blue phases”, was
non-existent.
In 1973, Coates and Gray came up with the name, “blue phases”, to indi-
cate this unusual state, and began to treat the phase as one of the liquid crystal
phases [10]. At last, the era of widespread study of blue phases had arrived.
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