Chemistry Reference
In-Depth Information
opaque liquid, and then finally a white solid crystal. Reinitzer was puz-
zled about what he observed: why were there two melting points between
the crystal (solid) and clear (liquid) states. He sent the sample together
with his observation to German physicist Otto Lehmann who later made
detailed observations by means of the polarizing microscope equipped with
a heat stage. He at last concluded that cholesteryl nanonoate in the tem-
perature range of 145
.
5
◦
C and 178
.
5
◦
C must be in a new state of matter.
After a few years of hesitation, he finally named this state of matter, the
liquid crystal
(Lehmann, 1900). Later somebody proposed that the term
“mesogenic state” might be an appropriate nomenclature for the new state,
because it may avoid possible confusion. In spite of this problem, people
have seemed to prefer the term liquid crystal due to its vivid description
and the term liquid crystal has since been widely adopted, while the term
mesogen or mesogenic is now used for a compound that is able to show
the liquid crystal state. Contemporary knowledge tells us that cholesteryl
nanonate actually exhibits two liquid crystal phases in the temperature
range of 178
.
5
◦
C and 145
.
5
◦
C. As the temperature decreases, the first blue
color is that of the blue phase of the liquid crystal, and the second violet-
blue color results from the cholesteric phase of the liquid crystal. More than
twenty liquid crystal phases have since been discovered. The blue phase and
cholesteric phase are two of them.
One enlightenment that can be drawn from the discovery of the liquid
crystal is that despite the fact that Reinitzer and Lehmann pursued dif-
ferent fields and were in different countries, the cooperation between them
inaugurated a new field of science — the liquid crystal. Actually the whole
development of the field of the liquid crystal has demonstrated this type of
cooperation.
As early as 1850, a German scientist discovered, in fact, the possibility
of the liquid crystal when he found that natural fats exhibited two melting
points. With increasing temperature, the substance starts to become cloudy
at around 52
◦
C and is completely opaque at 58
◦
C, and then becomes clear
at 62
.
5
◦
C. This observation should be the earliest record of the “discovery”
of the liquid crystal. At around the same time, the cholesterol derivative
exhibited a striking color when it cooled from the isotropic liquid state.
Unfortunately, these phenomena were not given enough attention or cor-
rectly explained. The researchers themselves did not realize that they were
approaching the entrance of a new field of science. Therefore, the discovery
of the liquid crystal should be attributed to Reinitzer and Lehmann.
