190
9 Molecular Flexibility and Material Properties
10
15
20
25
350
400
450
500
n
T
/ K
IL
cub*
SmC
Crystal
SmA
16 18 20
350
400
450
500
n *
IL
Cubic
SmA
SmC
Crystal
a)
b)
Ia3d
–
Ia3d
–
Fig. 9.9 Phase diagrams of a neat ANBC(n) against the chain length n [29] and b ANBC(16)–ntetradecane mixture against the effective chain length n ∗ [68]. The cub* phase is chiral but its space
group is unknown. The symmetry of the Cubic phase in the mixture (b) is not determined, resulting
in the coverage for both the I a3d and cub* phases of the neat series. Adapted from [33]
grams are mostly the same if drawn against n
∗ . In both phase diagrams, the addition
of alkane induces, around n
∗
∼ 7.5, a new phase, which was undoubtedly the SmA
phase for the n-heptane system [71]. These behaviors show that the chains serve
as a solvent in the liquid crystalline phases. The layer spacing (repeat distance) of
the mixture linearly depends on n
∗ and lie on the extrapolated dependence of neat
nCBs (n = 8, 9). The smooth variation of the layer spacing means that the QB picture holds not only for the general phase behavior but also for the structural aspect
(molecular aggregation). Since intermolecular interaction and segregation are evident in the crystalline state [73, 74], the above understanding of the SmA phase
results in the following view. The melting process of nCB in the phase sequence,
ordered crystal–SmA phase–N phase–isotropic liquid, is regarded as a shift of major
interaction from lyotropic (amphiphilic) to thermotropic one. Namely, the melting
of 8CB and 9CB to the isotropic liquid via SmA and N liquid crystals is a process
involving the thermotropic–lyotropic crossover.
The QB picture even offers the reason why the averaged chain length has been utilized as an essential parameter to characterize the liquid crystalline systems. Indeed,
in the study of the critical behavior of nCB mixtures, the averaged chain length, n
∗ ,
has been used to control their critical behavior [75]. Depending on n
∗ , the SmA –
N transition changes from the second-order to the first-order. The point where the
change happens is a triclitical point (Sect. 2.2.4). Although the range of n
∗ is narrow
in the research of in this context, n
∗ in a much broader range gives a unified phase
diagram, which interestingly includes the reentrant N phase that has finally been
discovered in this famous series after a long history of the research [19, 20].
9 Molecular Flexibility and Material Properties
10
15
20
25
350
400
450
500
n
T
/ K
IL
cub*
SmC
Crystal
SmA
16 18 20
350
400
450
500
n *
IL
Cubic
SmA
SmC
Crystal
a)
b)
Ia3d
–
Ia3d
–
Fig. 9.9 Phase diagrams of a neat ANBC(n) against the chain length n [29] and b ANBC(16)–ntetradecane mixture against the effective chain length n ∗ [68]. The cub* phase is chiral but its space
group is unknown. The symmetry of the Cubic phase in the mixture (b) is not determined, resulting
in the coverage for both the I a3d and cub* phases of the neat series. Adapted from [33]
grams are mostly the same if drawn against n
∗ . In both phase diagrams, the addition
of alkane induces, around n
∗
∼ 7.5, a new phase, which was undoubtedly the SmA
phase for the n-heptane system [71]. These behaviors show that the chains serve
as a solvent in the liquid crystalline phases. The layer spacing (repeat distance) of
the mixture linearly depends on n
∗ and lie on the extrapolated dependence of neat
nCBs (n = 8, 9). The smooth variation of the layer spacing means that the QB picture holds not only for the general phase behavior but also for the structural aspect
(molecular aggregation). Since intermolecular interaction and segregation are evident in the crystalline state [73, 74], the above understanding of the SmA phase
results in the following view. The melting process of nCB in the phase sequence,
ordered crystal–SmA phase–N phase–isotropic liquid, is regarded as a shift of major
interaction from lyotropic (amphiphilic) to thermotropic one. Namely, the melting
of 8CB and 9CB to the isotropic liquid via SmA and N liquid crystals is a process
involving the thermotropic–lyotropic crossover.
The QB picture even offers the reason why the averaged chain length has been utilized as an essential parameter to characterize the liquid crystalline systems. Indeed,
in the study of the critical behavior of nCB mixtures, the averaged chain length, n
∗ ,
has been used to control their critical behavior [75]. Depending on n
∗ , the SmA –
N transition changes from the second-order to the first-order. The point where the
change happens is a triclitical point (Sect. 2.2.4). Although the range of n
∗ is narrow
in the research of in this context, n
∗ in a much broader range gives a unified phase
diagram, which interestingly includes the reentrant N phase that has finally been
discovered in this famous series after a long history of the research [19, 20].