Chemistry Reference
In-Depth Information
1.4. POLYMORPHISM OF LIQUID CRYSTALS
MBBA, 4-methoxybenzylidene-4'-butylaniline was the first compound
which showed the liquid crystal phase at room temperature. The chemical
formulae of MBBA is as follows
MBBA shows only the nematic liquid crystal phase (denoted as N phase),
its phase sequence being
I
47
N
20
←→
←→
K
where I denotes the isotropic liquid phase, and K the crystal phase. The
figures are the transition temperatures in degrees Celsius between adjacent
phases. We will apply this expression when dealing with the phase sequences
hereafter.
A few liquid crystals have a more complicated phase behavior, showing
more than one liquid crystal phase. The series of terephthalylidene-bis-
alkylanilines (TBnA) is particularly interesting in presenting an unusually
broad polymorphism. For example, TPBA
has a phase sequence as follows
I
233
N
212
S
A
179
S
C
149
140
←→
61
←→
←→
←→
←→
←→
S
F
S
G
S
H
←→
K
,
where S
A
,
S
C
,
S
F
,
S
G
and S
H
denote the smectic A, smectic C, smectic F,
smectic G and smectic H phases.
Molecules with non-symmetric carbon atoms may exhibit a chiral
structure,
e.g.
, the compound (8SI) of chemical formulae
shows a phase sequence as follows
S
C
∗
←→
S
I
∗
←→
S
J
∗
←→
S
G
∗
←→
I
←→
Ch
←→
S
A
←→
K
,
