Liquid-crystalline polymorphism of 4-heptyloxybenzylidene-4′- alkyloxyanilines and their phase equilibrium with 4-octyloxyphenyl 4-nitrobenzoate

Article abstract of DOI:10.1016/j.tca.2012.01.008

This paper describes the synthesis and liquid-crystalline properties of the homologous series of 4-heptyloxybenzylidene-4′-alkyloxyanilines (7-n). Six of them are presented for the first time. Based on the polarization microscopy (POM and TOA methods) and the calorimetric (DSC) measurements following polymorphism has been detected: nematic, smectic C and smectic I mesophases. The presence of these mesophases was confirmed by the miscibility method, using 4-octyloxyphenyl 4-nitrobenzoate and terephtal-bis (4-butyloaniline) as a mesophase references. Extraordinary results have been found in the mixtures of the investigated compounds with 4-octyloxyphenyl 4-nitrobenzoate; Induced smectic A has been observed, which is connected with very strong intermolecular interactions. Additionally destabilization of nematic and smectic C phases was visible.

Full text of DOI:10.1016/j.tca.2012.01.008

Thermochimica Acta 531 (2012) 75–82
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Liquid-crystalline polymorphism of 4-heptyloxybenzylidene-4ꢀ-alkyloxyanilines
and their phase equilibrium with 4-octyloxyphenyl 4-nitrobenzoate
Joanna Godzwon, Monika J. Sienkowska, Zbigniew Galewski∗
Institute of Technology and Life Sciences, Lower Silesian Research Centre, Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper describes the synthesis and liquid-crystalline properties of the homologous series of 4-
heptyloxybenzylidene-4ꢀ-alkyloxyanilines (7-n). Six of them are presented for the first time. Based on
the polarization microscopy (POM and TOA methods) and the calorimetric (DSC) measurements follow-
ing polymorphism has been detected: nematic, smectic C and smectic I mesophases. The presence of
these mesophases was confirmed by the miscibility method, using 4-octyloxyphenyl 4-nitrobenzoate
and terephtal-bis (4-butyloaniline) as a mesophase references.
Received 13 September 2011
Received in revised form
13 December 2011
Accepted 5 January 2012
Available online 14 January 2012
Extraordinary results have been found in the mixtures of the investigated compounds with 4-
octyloxyphenyl 4-nitrobenzoate; Induced smectic A has been observed, which is connected with very
strong intermolecular interactions. Additionally destabilization of nematic and smectic C phases was
visible.
Keywords:
Liquid crystals
DSC
POM
© 2012 Elsevier B.V. All rights reserved.
Nematic
Smectics
Schiff bases
Phase diagrams
Phase transitions
1. Introduction
on the temperatures of phase transitions and the type of
mesophase were discussed. Recently we have published detailed
Schiff bases are a popular type of liquid-crystalline compounds,
due to a not very complicated synthesis and rich polymor-
phism. Since the 1970s the series of 4-alkyloxybenzylidene-4ꢀ-
alkylanilines, showing very rich polymorphism, were extensively
investigated. This class of compounds is especially important,
because many of them are acclaimed as the mesophase standards.
Demus observed the presence of the six different mesophases in
the 4-pentyloxybenzylide-4ꢀ-decylaniline (hexamorphism GBICAN
type) [1].
Similar properties were expected in the group of 4-
alkyloxybenzylidene-4ꢀ-alkyloxyanilines, which were investigated
since the 1960s. However, only derivatives with short alkyl chains
were synthesized and mesophases were inaccurately assigned.
In 2002 we published a preliminary article describing a group of
11 homologous series (121 derivatives) of 4-alkyloxybenzylidene-
4ꢀ-alkyloxyanilines [2]. Solely on the basis on the observation
of texture an influence of the length of both alkyloxy chains
investigations, with the special attention devoted to the proper
recognition of the smectic phases, of the following series of Schiff
bases: 4-dodecyloxybenzylidene- [3], 4-decyloxybenzylidene- [4],
4-nonyloxybenzylidene- [5], 4-octyloxybenzylidene- [6] and 4-
hexyloxybenzylidene-4ꢀ-alkyloxyanilines [7].
This publication describes a detailed analysis of the meso-
morphic behavior of 4-heptyloxybenzylidene-4ꢀ-alkyloxyanilines
(7-n). Our results on this family of compounds we presented in
2005 on the XVI Conference on Liquid Crystals in Stare Jabłonki
and described in the conference materials [8].
Until now only five derivatives of 7-n series with short alkyl
chains (from ethyl to hexyl derivatives) were described in litera-
ture.
In 1938 Weygand and Gabler published an article, describing
for the first time ethyl derivative (n = 2), which exhibited only a
nematic phase [9]. The same authors described this compound also
in 1940 [10]. In 1979 and 1981 Schifferdecker et al. published NMR
and dielectric relaxation behavior of 7-2 [11,12].
In 1964 Dave and Patel described butyl (n = 4) derivative, for
which they found only nematic mesophase [13]. In 1967 the same
authors synthesized propyl (n = 3), butyl (n = 4) and pentyl (n = 5)
derivatives [14]. Propyl (n = 3) and butyl (n = 4) derivatives exhib-
ited only nematic phase, while pentyl (n = 5) derivative displayed
nematic and one unknown smectic phase. Ten years later, in 1976
∗
Corresponding author at: Faculty of Chemistry, University of Wrocław, Wrocław,
Poland. Tel.: +48 71 3757346; fax: +48 71 3282348.
E-mail addresses: godzwonj@gmail.com (J. Godzwon),
monika.sienkowska@usa.dupont.com (M.J. Sienkowska), zg@wchuwr.pl
(Z. Galewski).
0040-6031/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2012.01.008

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J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
Table 1
Elemental analysis of 4-heptyloxybenzylidene-4ꢀ-alkyloxyanilines (7-n).
n
Calculated elemental composition in %
Found elemental composition in %
C
H
N
C
H
N
1
2
3
4
5
6
7
8
9
77.54
77.88
78.19
78.47
78.74
78.99
79.22
79.43
79.63
79.82
80.17
8.31
4.31
4.13
3.97
3.82
3.67
3.54
3.43
3.31
3.20
3.10
2.92
77.55
77.82
78.2
8.39
4.37
4.31
4.12
3.90
3.54
3.68
3.60
3.47
3.39
3.27
3.01
8.55
8.78
8.99
9.19
9.37
9.54
9.69
9.84
9.98
10.23
8.77
8.83
8.90
9.12
9.31
9.48
9.61
9.74
10.13
10.33
78.38
78.72
78.89
79.07
79.49
79.70
79.61
80.01
10
12
Malthête et al. described more precisely pentyl (n = 5) derivative,
in which nematic and smectic A phase were recognized [15].
From 1981 to 1986 Gandolfo, Grasso and Fasone described
calorimetric properties of five derivatives of 7-n in series of eight
publications [16–23]. In ethyl (n = 2) and propyl (n = 3) derivatives
only nematic phase was detected. The next derivatives, butyl (n = 4),
pentyl and hexyl (n = 6) (n = 5), except nematic phase, have one
more unknown smectic phase.
description of the set-up and experimental procedures are pub-
lished elsewhere [29].
In phase diagram investigations only mixtures of exact compo-
sition were prepared and studied. Very small samples were used
(∼10 mg). A very precise balance was used (Mettler AT20 with an
accuracy 2 × 10−6 g). All mesophases identified by POM were addi-
tionally confirmed by the Sackmann–Demus miscibility method
[26].
In 2006 Ajeetha et al. [24] described the synthesis, textu-
ral characterization, DSC measurements and dilatometry studies
of 4-heptyloxybenzylidene-4ꢀ-pentyloxyaniline (7-5). In the same
compound dilatometric properties were investigated in 2010 by
Madhavi Latha et al. [25].
3. Results and discussion
3.1. Liquid-crystalline properties
This publication describes the liquid-crystalline properties of
the homologous series of 11 derivatives of 7-n. Six compounds are
presented here for the first time (n = 1, 7, 8, 9, 10, 12). The main
aim of this work is to give a detailed description of the liquid-
crystalline polymorphism of these compounds, confirmed by the
Sackmann–Demus miscibility method [26]. The influence of the
alkyl chain length on the mesophase sequence and the change of
entropy of the phase transition is broadly discussed.
All phase transition parameters were obtained from the DSC
calorimetry measurements and the polarization microscopy (POM
and TOA). Both methods showed the same phase transition temper-
atures in the cooling and heating modes. Differences exist only for
the recrystallization due to the strong supercooling effects. Typical
DSC and TOA traces of decyl (n = 10) derivative are shown in Fig. 1.
The heating mode shows three signals. The first one at 92.6 ◦C is
connected with melting, which is indicated by the large value of
2. Experimental
2.1. Synthesis
HO
NO2
The synthesis of 7-n is outlined in Scheme 1. The details of this
synthesis have been presented elsewhere [27,28]. All final products
were purified by column chromatography, using silica gel (Fluka
60) and chloroform as eluent, followed by a recrystallization from
ethanol and heptane. The purity of all compounds was confirmed
by elemental analysis (Table 1) with the error limit less than 0.3%.
CnH2n+1Br
K2CO3
cyclohexanone
H2n+1CnO
NO2
HO
CHO
2.2. Equipment
C2H5OH
NH2NH2·H2O
Raney nickel
C H Br
K2CO3
cyclohexanone
7
5
Thermal transitions were determined by a Perkin-Elmer dif-
ferential scanning calorimeter (DSC7). Typical heating and cooling
rates were 5 ◦C min−1. Indium was used as an enthalpy standard.
Textures were identified under OLYMPUS BX60 microscope
equipped with a CCD JVC camera, connected with the PC com-
puter through an ELSA graphic card and LINKAM HTM600 hot stage
device with a TMS93 temperature regulator. The RS232 connec-
tions were used for the communication between the hot stage and
PC computer, which was crucial for the thermo-optic experiments
(TOA). The TOA experiments rely on the registration of two sig-
nals at the same time: temperature from the hot stage and light
intensity in the microscope. The first signal was detained from the
temperature regulator and the second from the photodiode with
the multimeter (Black Star 4503 Intelligent Multimeter). Detailed
NH2
H2n+1CnO
C7H15
O
CHO
C2H5OH
CH3COOH (catalyst)
C7H15
O
CH=N
OCnH2n+1
Scheme 1. Synthesis of 4-heptyloxybenzylidene-4ꢀ-alkyloxyanilines (7-n).

J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
77
Table 2
Phase transition parameters of 4-heptyloxybenzylidene-4ꢀ-alkyloxyanilines (7-n).
n
Melting
Recrystallization SmI
SmI
SmC
N
Iso
1
2
3
4
5
6
7
8
9
108.2 [47.23]
101.6 [40.88]
101.7 [29.55]
100.2 [42.08]
94.4 [30.21]
103.7 [31.33]
105.9 [37.10]
98.2 [36.00]
96.4 [52.20]
92.6 [48.68]
98.1 [55.21]
83.7 [37.23]
85.7 [36.65]
89.6 [22.54]
92.5 [19.37]
93.5 [16.65]
102.3 [26.13]
103.8 [36.59]
92.7 [31.12]
91.0 [18.53]
86.5 [21.44]
87.3 [30.25]
•
•
•
•
•
•
•
•
•
•
•
•
(101.4)[0.58]
120.6 [0.84]
109.2 [0.89]
116.6 [1.24]
111.8 [1.26]
115.8 [1.47]
113.2 [1.40]
114.7 [2.15]
112.8 [2.46]
112.9 [2.77]
110.0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
(97.2)[1.96]
99.7 [3.18]
104.5 [2.50]
106.3 [2.79]
108.4 [2.61]
109.4 [2.71]
110.3 [1.99]
109.0 [7.83]a
•
•
•
•
•
•
•
(95.8) [–]
(92.6) [1.48]
(91.2) [1.50]
(89.0) [1.71]
10
12
Enthalpy of the phase transition in kJ mol−1 are in square brackets and monotropic phase transition temperatures are in round brackets.
a
Total enthalpy value of two phase transitions.
125
120
isotropic
115
110
105
100
95
Nematic
SmC
Nematic
SmI
SmC
melting
melting
90
SmI
freezing
85
80
90
100
110
80
Temperature [ºC ]
2
4
6
8
10
12
Alkyl chain length-n
Fig. 1. DSC and TOA spectra of decyl (n = 10) derivative with heating and cooling
modes.
Fig. 2. Influence of the alkyl chain length on the mesophase sequence.
a
b
160
25
140
20
melting
120
Iso-N + N-SmC
15
100
80
10
5
N-SmC
60
Iso-N
freezing
40
SmC-SmI
10
0
0
2
4
6
8
10
12
0
2
4
6
8
12
Alkyl chain length-n
Alkyl chain length-n
Fig. 3. Influence of the alkyl chain length on the change of entropy of phase transitions.

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J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
130
120
110
100
90
130
130
120
110
100
90
a
b
c
isotropic phase
isotropic phase
isotropic phase
120
110
Nematic
Nematic
Nematic
SmA
SmA
100
90
80
70
60
50
SmA
SmC
SmC
SmC
80
80
melting
melting
70
70
Nematic
Nematic
melting
Nematic
60
60
50
0,0
50
0,0
0,2
0,4
0,6
0,8
1,0
0,2
0,4
0,6
0,8
1,0
7-4
0,0
0,2
0,4
0,6
0,8
1,0
x7-4
x7-6
x7-5
7-5
I
7-6
I
I
130
120
110
100
90
d
e
f
125
130
120
110
100
90
isotropic phase
isotropic phase
isotropic phase
120
115
110
105
100
95
Nematic
Nematic
Nematic
SmA
SmC
SmA
SmC
SmA
SmC
90
SmI
85
80
80
80
SmI
75
Nematic
Nematic
70
70
melting
melting
Nematic
melting
70
65
60
60
60
55
0,0
50
0,0
50
0,0
0,2
0,4
0,6
0,8
1,0
0,2
0,4
0,6
0,8
1,0
0,2
0,4
0,6
0,8
1,0
7-8
7-9
x7-7
x7-9
I
x7-8
I
I
7-7
g
h
125
125
isotropic phase
isotropic phase
120
115
110
105
100
95
120
115
110
105
100
95
Nematic
Nematic
SmC
SmA
SmA
SmC
90
90
85
85
SmI
80
80
SmI
75
75
melting
Nematic
70
70
melting
Nematic
65
65
60
60
55
0,0
55
0,0
0,2
0,4
0,6
0,8
1,0
0,2
0,4
0,6
0,8
1,0
7-10
7-12
x7-10
x7-12
I
I
Fig. 4. Phases diagrams of butyl (n = 4), pentyl (n = 5), hexyl (n = 6), heptyl (n = 7), octyl (n = 8), nonyl (n = 9), decyl (n = 10) and dodecyl (n = 12) derivatives with 4-octyloxyphenyl
4-nitrobenzoate (I).

J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
79
Fig. 5. Textures of mixture of butyl (n = 4) derivative with 4-octyloxyphenyl 4-nitrobenzoate.
the heating effect, 48.68 kJ mol−1. At the 110.3 ◦C and 112.9 ◦C two
DSC peaks are observed, which are identified as a phase transitions
into nematic and isotropic phases. Exactly the same thermal signals
have been observed in the thermo-optic scan. All phase transi-
tions are observed at the same temperatures as before. The cooling
modes for both DSC and TOA methods show richer polymorphism.
Iso-N and N-SmC phase transitions are detected at the same tem-
peratures as in the heating mode. Additionally SmC–SmI phase
transition can be detected by both methods. Smectic I appears at
91.2 ◦C, below the melting temperature. At 86.5 ◦C DSC scan shows
by very narrow and high peak, that the crystallization process takes
place. All details about phase transition parameters are shown in
Table 2.
In the investigated family three mesophases were detected:
nematic, smectic C and smectic I. Full phase situation is presented
in Fig. 2, which visualized the influence of the alkyl chain length.
Characteristic is the odd-even effect for the isotropization temper-
ature, with unusually low temperature for methyl (n = 1) derivative.
All derivatives show the presence of nematic phase. The smectic C
mesophase is visible from butyl (n = 4) derivative. Four members
of the investigated family, with the longest alkyl chains (n = 8, 9,
10, 12), have additionally smectic I mesophase. Most probably this
mesophase would be observed also in hexyl (n = 6) and heptyl (n = 7)
derivatives, but their significantly high melting and freezing tem-
peratures exclude this possibility. The melting temperature has also
very interesting dependence. Heptyl (n = 7) derivative, that features
both alkyl substituents of the same length, has the highest value.
The high “melting” points of the 6 and 7 homologs no doubt come
from the more efficient crystal packing of these homologs due to
their more “symmetric” nature. The molecular order in the SmC
phase must therefore be similar to that in the crystal to account
for the observed small change in the entropy going from solid
to mesophase. Such behavior exists in other similar homologous
series [3–7].
3.2. Entropic effects
Phase transitions between mesophases are associated with the
changes in molecular ordering. This can be illustrated by the
change of entropy values (Fig. 3). Fig. 3a and b shows the depen-
dence of the change of entropy of phase transitions from the
alkyl chain length. This dependency is especially significant for
the melting (Fig. 3a). Methyl (n = 1) derivative has the change of
entropy value of 123.9 J mol−1 K−1. The decrease of this param-
eter to 82.2 J mol−1 K−1 for pentyl (n = 5) derivative is caused by
the increase of the alkyl chain length. Next, almost monotoni-
cally increase of this parameter with alkyl chain length up to
148.7 J mol−1 K−1 for dodecyl (n = 12) derivative is observed. This
curve shows a small odd-even effect. The change of entropies of
freezing shows similar properties. However, the change of entropy
values for propyl (n = 3), butyl (n = 4), pentyl (n = 5), nonyl (n = 9),
decyl (n = 10) and dodecyl (n = 12) derivatives are much lower
compared to melting. It may be connected with solid state poly-
morphism.
The phase transitions with the smallest change of entropy are
shown in Fig. 3b. Typical is the influence of the alkyl chain length
on the change of entropy value of phase transition Iso-N. This
parameter increases from 1.5 J mol−1 K−1 for methyl (n = 1) deriva-
tive to 7.2 J mol−1 K−1 for dodecyl (n = 10) derivative. For the first
seven derivatives regular odd-even effect is observed. The change of
entropy values of phase transition N(Iso)-SmC are higher (Fig. 3b).
For this transition the odd-even effect is also observed. Dode-
cyl (n = 12) derivative shows extraordinary high entropic effect of
isotropization. This change of entropy is about four times bigger
than change of entropy value for derivatives with short alkyl chain.
For these phase transitions there is no additivity of entropic effect:
ꢀSIso-N + ꢀSN-SmC =/ ꢀSIso-SmC

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J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
a
b
200
180
160
140
120
100
200
isotropic phase
isotropic phase
180
160
140
120
100
SmC
SmC
SmA
SmI
SmA
SmI
Nematic
Nematic
SmF
G
SmF
G
glass
glass
SmI
SmI
0,8
0,0
0,2
0,4
0,6
1,0
0,0
0,2
0,4
0,6
0,8
1,0
7-8
II
x7-8
7-9
II
x7-9
200
c
d
200
isotropic phase
isotropic phase
180
160
140
120
100
180
160
140
120
100
SmC
SmI
SmC
SmA
SmA
SmI
SmF
Nematic
Nematic
SmF
G
G
glass
glass
SmI
0,8
SmI
0,0
0,2
0,4
0,6
0,8
1,0
0,0
0,2
0,4
0,6
1,0
7-10
II
x7-10
7-12
II
x7-12
Fig. 6. Phases diagrams of octyl (n = 8), nonyl (n = 9), decyl (n = 10) and dodecyl (n = 12) derivatives with terephtal-bis-(4-butylaniline) (II).
and investigated compounds exist in the similar temperature
Phase transition SmC–SmI has a similar change of entropy as
range.
phase transition Iso-N (Fig. 3b). It is difficult to define whether the
change of entropy of this phase transition depends on the alkyl
chain length. The SmC–SmI phase transition is detected only in last
three derivatives and the change of entropy of this transition is
Presented diagrams (Fig. 4) show strongly nonlinear properties.
Induced smectic A is observed. It is probably connected with the
specific interaction of nitro or ester group of standard I with the
investigated azometine. Temperature range of existence of smectic
A mesophase in the mixture is significantly greater than in the pure
compounds.
about ∼4 J mol−1 K−1
.
All diagrams have the same type of topology, therefore influence
of the alkyl chain length is not significant.
3.3. Phase diagrams
These phase diagrams can be explained as the creation of solid
solutions (or more precisely mesomorphic solutions) with the max-
imum of clearing temperature, where “solidus” and “liquidus” lines
intersect. But from the molecular point of view this behavior can
also be explained as the some kind of the strong intermolecular
interaction.
For the proper mesophase identification Sackmann–Demus
miscibility method was applied [8]. Fig. 4 shows phase dia-
grams of butyl (n = 4), pentyl (n = 5), hexyl (n = 6), heptyl
(n = 7), octyl (n = 8), nonyl (n = 9), decyl (n = 10) and dodecyl
(n = 12) derivatives with 4-octyloxyphenyl 4-nitrobenzoate (I),
as a standard of mesophases N and SmA [30]. The standard

J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
81
Fig. 7. Textures of mixture of octyl (n = 8) derivative with terephtal-bis-(4-butylaniline).
The presence of induced smectic A is connected with the disap-
pearance nematic phase on both sides of the diagram. Additionally,
smectic C phase, existing in the investigated compounds, disap-
pears very quickly. Very often investigated diagrams contain three
mesophases at the same temperature and concentration. These
points we should interpret according to the phase rule. Short hor-
izontal line (invariant line) reduces two double lines into one
twofold. Such diagrams were very precisely described in papers of
Billard school [31]. In our figures, because of the clarity, invariant
lines have been reduced to the points.
These both phenomena very weakly depend on the alkyl chain
length of the investigated Schiff bases. However, this kind of depen-
dence is apparent in the case of reducing the area of nematic phase.
Distance between invariant lines Iso-N-SmA and N-SmA–SmC is
reduced with the alkyl chain length of the derivative.
The composition of the eutectic points is nearly the same in each
diagram.
Typical textures of all four mesophases are presented in Fig. 5.
Fig. 5a shows a typical schlieren texture, characteristic for the
nematic phase. Fig. 5b presents a fan texture, which is typi-
cal for smectic A mesophase. The orthogonal type of smectics is
confirmed by the homeotropic orientation of molecules, what is
observed as a black area in the center of the picture. Fig. 5c dis-
plays the change of the fan texture of smectic A phase into a
broken fan texture, typically observed in smectic C phase. The black
areas observed for smectic A phase are replaced by a schlieren
texture. This very specific pattern was found only in the smec-
tic C phase. The SmC–SmI phase transition is shown in Fig. 5d.
Textures of nematic, smectic A and smectic C phases are so char-
acteristic, that their interpretation is unambiguous. However, the
presence of smectic I phase has to be confirmed by the miscibility
method.
The investigated compounds do not form solid solutions with
the standard I. On the diagrams simple eutectic system is visible.

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J. Godzwon et al. / Thermochimica Acta 531 (2012) 75–82
For the smectic
I
phase identification terphtal-bis-(4-
point. The composition at this point is constant and weakly
oscillates around a value of 0.2.
2. With standard II
(d) Investigated diagrams confirm presence of the SmI in octyl,
nonyl, decyl and dodecyl derivatives.
(e) Vitreous properties of lowest mesophases in the broad
concentrations range are observed.
butylaniline) was used as a standard II [1,32,33]. The phase
diagrams, which are shown in Fig. 6, confirm the presence of
smectic C and smectic I phases in the investigated derivatives.
Temperatures of phase transitions occurring in standard II are
much higher than in the investigated compounds. Therefore, the
obtained diagrams are less readable, with narrow and long areas of
mesophases. Because of the clarity invariant lines have been also
reduced to the points. However, the areas of the smectic C and I
phases are easy recognizable.
Additionally, on the discussed diagrams nematic and smectic
A phases are separated by a narrow line. The influence of the
alkyl chain length on the stabilization of smectic A phase and the
destabilization of nematic phase are visible. Destabilization of G
mesophase is also observed. Also, characteristic for these mixtures
are vitreous transitions.
Typical textures of the investigated mixtures of 4-
heptyloxybenzylidene-4ꢀ-alkyloxyanilines with the standard
II are shown in Fig. 7. Fig. 7a presents texture of nematic phase,
which appears as a round area with schlieren texture. The round
area increases on cooling. The black area is connected with a
homeotropic orientation of molecules. Fig. 7b presents a fan-
shaped texture, which is typical for smectic A mesophase. Still the
black areas of a spontaneous homeotropic orientation of molecules
are observed. On Fig. 7c fan texture of smectic A is replaced by
broken fan texture, which is typical for smectic C mesophase. In
place of the black areas observed on Fig. 7b is now a schlieren
texture very typical for smectic C phase. The SmC–SmI phase
transition proceeded in a very characteristic way (Fig. 7d). Broken
fan texture areas of smectic C change into polygonal texture,
typical of smectic I phase. Fig. 7e and f shows textures of the
smectic F and G mesophases, which are ambiguous.
(f) The increase of the alkyl chain length has the influence on
the stabilization of smectic A phase and the destabilization
of the nematic phase. The increase of the alkyl chain length
also destabilizes the G mesophase.
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Investigated compounds have following phases: nematic
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(c) The investigated compounds do not form solid solutions
with the standard I. All mixtures show a simple eutectic