Chemistry Reference
In-Depth Information
discotic liquid crystal molecules are about 1 nm in thickness and a few nm
in diameter.
1.3.3. Amphiphilic liquid crystals
Another important member of the liquid crystal family is the solution of
amphiphilic molecules. The amphiphilic molecules are tadpole-like. A polar,
hydrophilic group is at one end of the amphiphilic molecule while a non-
polar, hydrophobic group is at the other end. Two examples are shown in
Figure 1.3. Soap in solution, for example, is a liquid crystal. One end of this
molecule, -COO-Na
+
is a polar group and is soluble in water, while the
other end is a hydrocarbon paran group CH
3
(CH
2
)
14
−
, dissolved in water.
The liquid crystalline materials exhibit the liquid crystal phase in
different ways. Some of them exhibit the liquid crystal phase at a
certain range of temperatures, while some exhibit the liquid crystal
phase according to their concentration in solution. The former are called
thermotropic liquid crystals, and the latter lyotropic liquid crystals. The
-
O
+
Na
C - C
15
-H
31
O
(a)
+
-
O
CH
3
O
C-C
15
H
31
O
CH
2
C
CH
3
-N-CH
2
O-P-O
CH
O
CH
2
C-C
15
H
31
CH
2
CH
3
O
O
(b)
Figure 1.3.
Two amphiphilic liquid crystal molecules:
(a) sodium laurate;
(b)
dipalmitoylphosphatidylcholine. (From Collings, 1990.)
