Mesomorphic and structural properties of liquid crystal possessing a chiral lactate unit

Article abstract of DOI:10.1016/j.molstruc.2012.01.017

The mesomorphic and structural properties of the chiral lactic acid derivative 4′-(1-(octyloxy)-1-oxopropan-2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate have been studied. The compound shows the blue phase (BPII), the cholesteric (N), the TGB_A and the paraelectric SmA phases over a broad temperature range. Polarising optical microscopy, differential scanning calorimetry, optical transmission, X-ray diffraction and dielectric spectroscopy studies have been performed. In the SmA phase the layer spacing (d) values are found to be slightly temperature dependent and suggest that there is no bi-layer association present in the mesophase. In the TGB_A phase, the d values show strong temperature dependence near SmA-TGB_A phase transition, indicating pre-transitional effect. The temperature dependence of scattered X-ray intensities indicate the appearance of long range smectic ordering at the N-TGB_A phase transition. Near the TGB_A-SmA phase boundary strong SmA fluctuations predominate. This behaviour is also observed from the temperature dependence of the d values. The transverse correlation lengths, ξ_⊥, diverge near the N-TGB_A phase transition indicating second order phase transition.

Full text of DOI:10.1016/j.molstruc.2012.01.017

Journal of Molecular Structure 1013 (2012) 119–125
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Mesomorphic and structural properties of liquid crystal possessing a chiral
lactate unit
c
c
Banani Das a, Anamika Pramanik b, Malay Kumar Das b, , Alexej Bubnov , Vera Hamplová ,
⇑
ˇ
Miroslav Kašpar c
a Department of Physics, Siliguri Institute of Technology, Siliguri, Darjeeling 734 009, West Bengal, India
b Department of Physics, University of North Bengal, Siliguri, Darjeeling 734 013, West Bengal, India
c Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Prague, Czech Republic
a r t i c l e i n f o
a b s t r a c t
The mesomorphic and structural properties of the chiral lactic acid derivative 40-(1-(octyloxy)-1-oxopro-
pan-2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate have been studied. The compound shows the blue
phase (BPII), the cholesteric (Nꢀ), the TGBA and the paraelectric SmAꢀ phases over a broad temperature
range. Polarising optical microscopy, differential scanning calorimetry, optical transmission, X-ray dif-
fraction and dielectric spectroscopy studies have been performed. In the SmAꢀ phase the layer spacing
(d) values are found to be slightly temperature dependent and suggest that there is no bi-layer associa-
tion present in the mesophase. In the TGBA phase, the d values show strong temperature dependence near
SmAꢀ–TGBA phase transition, indicating pre-transitional effect. The temperature dependence of scattered
X-ray intensities indicate the appearance of long range smectic ordering at the Nꢀ–TGBA phase transition.
Near the TGBA–SmAꢀ phase boundary strong SmAꢀ fluctuations predominate. This behaviour is also
observed from the temperature dependence of the d values. The transverse correlation lengths, n\,
diverge near the Nꢀ–TGBA phase transition indicating second order phase transition.
Article history:
Received 28 October 2011
Received in revised form 15 January 2012
Accepted 17 January 2012
Available online 28 January 2012
Keywords:
Liquid crystals
Phase transition
TGBA phase
X-ray diffraction
Differential scanning calorimetry
Dielectric properties
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
differing in number of the lactate groups as chiral centres have
been attracting attention as they show a rich variety of the polar
Liquid crystalline (LC) materials exhibiting a great variety of
structures are strongly susceptible to external fields as well as
surface interactions, and provide multiple functionality. Thermo-
dynamically liquid crystalline materials are located between the
three-dimensionally ordered solid state (crystal) and the isotropic
liquid. For particular molecules assembled in specific architectures,
permanent dipole moment can appear thus forming structures
with a polar order, namely paraelectric, ferroelectric or antiferro-
electric phases [1]. Such materials can be utilised as a self-assem-
bling media combining the necessary order and fluidity on a
molecular (nano-scale) level [2,3].
While designing chiral liquid crystalline materials, the type of
chiral fragment used in the molecule plays a very important role
in determining its mesomorphic behaviour. In 1988 Taniguchi
et al. [4] synthesized and studied series of compounds with phe-
nyl-40-alkoxybiphenyl-4-carboxylate as a molecular core and one
lactate group as a chiral centre. These compounds possess a broad
range of the paraelectric smectic Aꢀ (SmAꢀ) and ferroelectric smec-
tic Cꢀ (SmCꢀ) phases. During the last years, lactic acid derivatives
liquid crystalline mesophases [5–12]. Use of the lactic unit as a
precursor of chiral centre have two advantages with respect to
other types of chiral centres: (i) they minimise the cost, as the price
ratio to the most commonly used chiral precursor material (S)-2-
octanol is at least 1:100 and (ii) lactic acid-based LCs usually show
no aging and are highly stable, thermally as well as chemically.
Lactate based chiral moiety has provided many materials with a
very rich variety of the liquid crystalline mesophases [13–19].
Several new liquid crystalline materials containing one, two or
three chiral centres and having one or two lactate groups attached
to the molecular core by the ether linkage group have been synthe-
sized and studied [20,21].
However, several basic questions are still open, especially those
concerning the interactions between the molecular core and ali-
phatic chains, relation between the chemical structure, mesophase
behaviour and the physical properties of the polar mesophases.
Therefore, the investigation of the structure–property relationship
for lactic acid derivatives possessing liquid crystalline behaviour is
still of great significance for further progress, both for the under-
standing of the basic properties as well as for their practical use
in potential applications. The understanding of the mesophase
nano-scale organisation will enable generalisation of relation
⇑
Corresponding author. Tel.: +91 3532582605; fax: +91 3532699001.
E-mail address: mkdnbu@yahoo.com (M.K. Das).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.01.017

120
B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
between molecular structure and macroscopic properties of liquid
crystalline materials. Molecules with pronounced features related
to the macroscopic properties could then be synthesised.
In order to contribute towards better understanding of struc-
ture – property relationship, the mesomorphic and structural
properties of the chiral lactic acid derivative, namely 40-(1-(octyl-
oxy)-1-oxopropan-2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate,
possessing liquid crystalline behaviour have been studied by polar-
ising optical microscopy, differential scanning calorimetry, optical
transmission, X-ray diffraction and dielectric spectroscopy.
(dd, 4H, ortho to –Ar); 7.23 (d, 2H, ortho to –OCO–); 6.99 (d, 2H,
ortho to –OCH2); 6.87 (d, 2H, ortho to –OH); 5.00 (brs, 1H, OH);
4.05 (t, 2H, CH2O); 1.20–1.80 (m, 16H, CH2); 0.90 (t, 3H, CH3).
1H NMR of final product (300 MHz, CDCl3): 8.15 (d, 2H, ortho to
–COO); 7.56 and 7.50 (dd, 4H, ortho to –Ar); 7.24 (d, 2H, ortho to –
OCO–); 6.96 (dd, 4H, ortho to –O); 4.80 (q, 1H, CHꢀ); 4.17 (m, 2H,
COOCH2); 4.03 (t, 2H, CH2OAr); 1.80 (m, 4H, CH2CH2O); 1.62 (d,
3H, CH3Cꢀ); 1.20–1.60 (m, 24H, CH2); 0.87 (m, 6H, CH3).
Chemical formula of the final product indicating the carbon
atom numbers and the chemical shift (d) obtained from 13C NMR
spectroscopy (300 MHz, CDCl3) are presented in Table 1.
2. Experimental
2.2. Mesomorphic properties
2.1. Material under the study
The sequence of phases and phase transition temperatures were
identified by observing the textures and their changes under the
polarising optical microscope. The LINKAM LTS E350 heating stage
with TMS-93 temperature programmer was used for temperature
control, which enabled temperature stabilisation within 0.1 K. In
addition, free – standing films were also prepared, in which the
liquid crystalline material was mechanically spread over a circular
hole (diameter 3 mm) in a metallic plate. The phase transition tem-
peratures were checked by Differential Scanning Calorimetry (Pyris
Diamond Perkin-Elmer 7) on cooling/heating runs at a rate of
5 K minꢂ1 in a nitrogen atmosphere. The sample (5 mg) was her-
metically sealed in an aluminium pan and placed in a nitrogen
atmosphere. The temperature was calibrated on extrapolated
onsets of the melting points of water, indium and zinc. The enthal-
General synthetic procedure for chiral lactic acid derivative is
presented in Fig. 1. The synthesis started from 4-n-decyloxybenzoic
acid. The compound on reaction with an excess of thionylchloride
and
4,40-biphenol
yielded
4-(40-hydroxybiphenyl)4-n-dec-
yloxybenzoate. Optically active octyl lactate was prepared from
commercial (S)-(+)-lactic acid by azeotropical esterification with
octylalcohol. DEAD (diethyl azodicarboxylate) supported coupling
in the presence of triphenylphosphine in tetrahydrofurane followed
by column chromatography gave the final compound. However, the
detailed synthetic procedure for the 40-(1-(octyloxy)-1-oxopropan-
2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate (material under the
study) has been described in details in our earlier publication [20].
The raw product was purified by column chromatography on
silicagel (Kieselgel 60) using a mixture of dichloromethane and
ethanol (99:1) as an eluent. Recrystallization was made twice from
ethanol producing white powder. The chemical purity of the mate-
rial was checked by high pressure liquid chromatography (HPLC),
which was carried out using a silica gel column (Bioshere Si 100-
py change [DH] was calibrated on enthalpies of melting of water,
indium and zinc.
2.3. Optical transmission
5
l
m, 4 ꢁ 250, Watrex) with a mixture of 99.9% of toluene and
Optical transmission method [22] on samples with planar and
homeotropic alignment was also used for identification of the
liquid crystalline phases. A linearly polarised He–Ne laser beam
(k = 632.8 nm) was used as a light source and directed onto a
homogeneously (or homeotropically) aligned Indium Tin Oxide
(ITO) coated liquid crystalline cell (purchased from AWAT Co.
Ltd., Warsaw, Poland) placed between two crossed linear polariz-
ers. The temperature of the cell in a brass thermostat was con-
trolled by Eurotherm PID 2216e temperature controller, which
enabled temperature stabilisation within 0.2 K. The light trans-
mittance was measured by a photodiode detector and recorded
0.1% of methanol as an eluent, and the eluting products were de-
tected by a UV–VIS detector (k = 290 nm). The chemical purity of
the synthesised compound was found to be 99.6% under these
conditions.
Structures of the intermediates and the final liquid crystalline
material were checked by the Nuclear Magnetic Resonance (NMR)
spectroscopy. A 300 MHz Varian spectrometer with tetramethylsil-
ane as internal standard was used for 1H and 13C NMR studies.
1H NMR of 4-(40-hydroxybiphenyl)4-n-decyloxybenzoate
(300 MHz, CDCl3): 8.16 (d, 2H, ortho to –COO); 7.55 and 7.43
O
O
OH
HO
OH
SOCl2
O
O
O
OH
DEAD
Ph3P
THF
O
HO
*
O
O
O
O
O
O
*
O
Fig. 1. Schematic illustration of synthetic procedure for 40-(1-(octyloxy)-1-oxopropan-2-yloxy) biphenyl-4-yl 4-(decyloxy)benzoate.

B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
121
Table 1
Chemical shift d (ppm) for 40-(1-(octyloxy)-1-oxopropan-2-yloxy)biphenyl-4-yl 4-(decyloxy)benzoate from 13C NMR.
Carbon no.
d (ppm)
Carbon no.
d (ppm)
1
10
11
12
13
14
15
16
17
18
14.27
68.57
19
20
21
22
23
24
25
26
27
34
138.51
134.12
127.95
115.60
163.80
18.83
72.97
172.47
65.65
157.46
114.54
132.50
121.81
165.21
150.40
122.22
128.42
14.31
digitally by a Keithley 2000 multimeter. The transmitted light
intensity was measured as a function of temperature. From the
temperature dependence of the transmitted light intensity, we
could identify the phase transition temperatures, especially those
transitions, which could not be detected by DSC. Such method
has been successfully used in our investigations of other liquid
crystalline molecules like hockey-stick shaped mesogens [23,24].
checked and the related enthalpies have been measured using
DSC. The respective thermogram on heating and cooling runs is
presented in Fig. 3. Phase transition temperatures are shown in
Table 2. On cooling from the isotropic (Iso) phase the studied LC
material exhibited the blue phase (BPII), the cholesteric phase,
the twist grain boundary smectic A (TGBA) phase and the paraelec-
tric SmAꢀ phase.
In Fig. 4, several characteristic microphotographs of the meso-
phase textures of the sample in planar alignment (a–e) and free
standing film (f) are presented. In particular, a very characteristic
platelet texture of the blue phase (Fig. 4a), oily streaks texture of
the cholesteric phase (Fig. 4c) and filament texture of the TGBA–
SmAꢀ phase transition (Fig. 4f) helped to unambiguously detect
the type of mesophases. Due to quite low enthalpies of the Iso–
BPII, Nꢀ–TGBA and TGBA–SmAꢀ phase transitions, the respective
transitions were hardly detectable by DSC but were well defined
by polarising optical microscopy. Again, the optical transmission
studies were quite helpful for the identification of some of the
phase transitions which were not clearly detected from DSC
measurements.
2.4. Dielectric spectroscopy
The temperature dependence of the real part of complex per-
mittivity (eꢀ e0–ie00) was measured on cooling using a Schlumber-
=
ger 1260 impedance analyzer at a frequency of 160 Hz. Planar
sample of thickness 12
measurement.
lm was used for dielectric spectroscopy
2.5. X-ray diffraction
X-ray diffraction measurements were done on the samples
filled into Mark capillary tubes of 0.7 mm diameter, in the presence
of a magnetic field (1 T). The temperature of the sample was regu-
lated by a temperature controlled heating stage. The X-ray patterns
were recorded on a 2D area detector (HI – Star, Siemens AG) using
3.2. Optical transmission study
Ni-filtered Cu K
a radiation (wavelength k = 1.5418 Å). From the
Fig. 5 shows the temperature dependence of the transmitted
X-ray diffraction studies the smectic layer spacing (d) in the TGBA
and SmAꢀ phases (or apparent molecular length (l) in the case of
blue phase and the cholesteric (Nꢀ) phase) and the average inter-
molecular distance between the long axes of neighbouring parallel
molecules (D) were calculated from the position of the small angle
(h = 0.2–4.5°) and wide angle diffraction peaks, respectively for all
the phases.
The MOPAC/AM1 model was used to ascertain the length of LC
molecules corresponding to the state with minimum energy. In
Fig. 2, picture of molecule with the axis corresponding to the small-
est principal moment of inertia is presented. Taking into account
the most extended conformer (length of the molecule in the direc-
tion of the long molecular axis), the length of molecule is calcu-
lated to be 43 Å.
intensity from planar as well as on homeotropic cells (8.9 lm
thickness) placed between two crossed linear polarizers. Interest-
ingly, the Nꢀ–TGBA and TGBA–SmAꢀ phase transition temperatures,
which were not clearly detectable from DSC measurements, could
be identified clearly. However, the Iso–BPII, BPII–Nꢀ phase transi-
tions, which were visible in DSC measurement (Fig. 3) were not
clearly identifiable in the optical transmission method. Hence,
the conclusion regarding the existence of the different mesophases
is based on observations from all the three used methods, namely
the study of textures and their changes under polarising optical
microscope, DSC runs and optical transmission studies.
3.3. X-ray diffraction
Fig. 6(a–c) shows the X-ray diffraction photographs of the una-
ligned sample obtained in the BPII, TGBA and SmAꢀ phases at 86 °C,
70 °C and 50 °C respectively. From the X-ray diffraction patterns it
is clear that it was not possible to align the compound with a mag-
netic field of about 1 T. The pattern obtained immediately below
the clearing temperature (Fig. 6a) i.e. in the BPII show the presence
of diffuse rings both in the small and wide angle regions typical for
the non-oriented samples. The absence of sharp inner ring
3. Results and discussion
3.1. Texture and DSC studies
The phase sequences of the materials were determined from
characteristic textures and their changes observed under a polaris-
ing optical microscope. Phase transition temperatures have been

122
B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
Fig. 2. Conformation of the molecule after energy minimisation using MOPAC/AM1 method.
phase (the type of the mesophase has been determined from typ-
38
36
34
32
30
28
ical textures obtained on free standing films), the d values initially
increase slowly (31.7 Å) with decrease in temperature. However,
we observe a rapid increase in d (37.7 Å) as the TGBA–SmAꢀ phase
transition is approached. In fact, its value coincides with the SmAꢀ
layer spacing. Thus within the TGBA phase, the ratio d/l ꢄ 0.74–0.88
which is typical of monolayers and also is a signature of the SmA
nature of the blocks of the TGBA phase. The effective molecular
length (l) in case of the BPII and Nꢀ phases increases with decrease
in temperature. The increase in l values in going from the Nꢀ to
TGBA phase has also been reported by Shankar Rao et al. [25].
The intermolecular distance, i.e. the average lateral distance be-
tween the long axes of molecules, D, decreases with decrease in
temperature, as expected.
Iso
TGBA
N*
SmA*
BPII
Cryst
30
40
50
60
70
80
90
T / oC
Fig. 3. DSC thermograms on heating and cooling cycles taken at a rate 5 K minꢂ1
.
Vertical arrows indicate the Iso–BPII, BPII–Nꢀ, Nꢀ–TGBA and TGBA–SmAꢀ phase
The temperature dependence of the intensity of the inner ring
(with nearly same exposure time) is presented in Fig. 10. It is ob-
served that the X-ray intensity is nearly constant in the Nꢀ phase.
However, the intensity values appear to show a discontinuous in-
crease at the transition from Nꢀ to TGBA phase. Within the TGBA
phase the X-ray intensity increases with decrease in temperature
and this increase is quite rapid as the TGBA–SmAꢀ phase transition
is approached. It may be mentioned here, that, the reason for the
appearance of the TGBA phase is that a direct cholesteric–smectic
phase transition cannot occur in a continuous way since the chole-
steric twist of the director is not compatible with the smectic lay-
ering. Thus we observe a definite increase in the scattered X-ray
intensities at the onset of the TGBA phase at the Nꢀ–TGBA phase
boundary signifying the appearance of long range order in layering
within this phase. Again, as observed from Fig. 10, there is a signif-
icant increase in the intensity values near the TGBA–SmAꢀ phase
transition. SmAꢀ fluctuations dominate in this region as the twist
of the smectic blocks within the TGBA phase gradually unwinds
and smectic A like ordering appears. This behaviour again verifies
the existence of the TGBA phase. Similar behaviour is also observed
in the d values as mentioned in the previous paragraph.
transitions subsequently on heating (?) and cooling ( ).
indicates that this mesophase is rather fluid like. We have also ob-
tained a similar pattern in the Nꢀ phase which is expected. Below
78 °C we observe relatively sharp inner ring and a diffuse outer
ring in the X-ray diffraction pattern (Fig. 6b) and the intensity of
the inner ring increases with decreasing temperature. The pattern
represents the unoriented TGBA phase as observed from polarising
optical microscopy. The intense peak in the small angle region cor-
responds to the smectic layer thickness in the TGBA phase. On fur-
ther cooling (Fig. 6c) the outer diffraction pattern remains the
same but the inner ring becomes distinctly sharper and hence this
pattern suggests the appearance of the non-oriented SmAꢀ phase.
Fig. 7 shows the X-ray diffraction intensity profiles obtained
from a linear scan of the diffraction patterns of the non-oriented
sample in different mesophases. The intensity profile reveals the
presence of relatively sharp reflections at small angles (2h ꢃ 3–
4°) in the TGBA and SmAꢀ phase, clearly indicating the layered
structure, in comparison to the diffuse ring obtained in the case
of the BPII and Nꢀ phases. The diffuse outer scattering at wide an-
gles (2h ꢃ 18–24°) corresponds to the average intermolecular dis-
tance D between the long axes of neighbouring parallel molecules.
The values of the effective molecular length (l) in case of the
BPII and Nꢀ phases and the smectic layer thickness (d) in the TGBA
and SmAꢀ phases as well as the intermolecular distance between
the long axes of the neighbouring molecules D, at different temper-
atures were determined. The temperature dependence of the l or d
values and intermolecular distance D are presented in Figs. 8 and 9
respectively. Interestingly, the layer spacing of the SmAꢀ phase is
found to have a slight temperature dependence with the d values
changing from 37.5 Å at the TGBA–SmAꢀ phase transition to 39 Å
within the phase. The increase in layer spacing values of the SmAꢀ
phase on cooling is perhaps due to stretching of the aliphatic
chains of the molecule. Within the temperature range of the TGBA
The longitudinal (n||) as well as the transverse in-plane (n\)
correlation length in different mesophases have been determined
from a linear scan of the inner and outer diffraction peaks. The
intensity profile I(q) was then fitted to a Lorentzian form with a
quadratic background viz.,
a1
IðqÞ ¼
þ a3q2 þ a4q þ a5
ð1Þ
2
a2 þ ðq ꢂ q0Þ
where q is the magnitude of the scattering vector. Here a1, a2, qo, a3,
a4 and a5 are the fitting parameters, which were adjusted to obtain
the best fit. The transverse correlation length is defined as
n = 2
vant temperature region. As expected, the correlation lengths for
p
(a2)ꢂ1/2. Fig. 11 shows the results for n\ and n|| over the rele-
Table 2
Sequence of phases, phase transition temperatures (°C), transition enthalpies [
heating) for the studied compound. (‘‘d’’ the phase exists).
D
H (J/g)] (measured on cooling with DSC (5 K minꢂ1)) and melting point m.p. (°C) (measured on
m.p.
Cr
SmAꢀ
TGBA
Nꢀ
BPII
Iso
41.7
d
37.8
d
58.5
d
79.8
d
85.3
d
86.1
d
[+24.06]
[ꢂ23.87]
[ꢂ0.33]
[ꢂ0.01]
[ꢂ0.96]
[ꢂ0.01]

B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
123
Fig. 4. Microphotographs of textures observed under the polarising optical microscope: (a) platelet texture of the blue phase (BPII) at 85.5 °C; (b) the BPII–Nꢀ phase transition
at 85 °C;(c) the oily streaks texture of the cholesteric phase (Nꢀ) at 83 °C ;(d) the texture of the TGBA phase at 75 °C; (e) the TGBA–SmAꢀ phase transition at 58 °C; (f) the
filament texture of the TGBA–SmAꢀ phase transition at 58 °C (free standing film).The width of all the photos is about 350
lm.
transition point, as expected for a second order phase transition.
These observations have also been supported by enthalpy and opti-
cal transmission measurements. The longitudinal correlation
length, n||, increases rapidly at the Nꢀ–TGBA phase transition from
about 125 Å to nearly 325 Å near the TGBA–SmAꢀ phase transition.
This rise continues even in the SmAꢀ phase and reaches a value of
about 350 Å at saturation. It is necessary to mention that for all
studied phases, the correlation lengths are expected to be much
longer. Possible explanation for this discrepancy may be due to
0.025
0.020
0.015
0.010
0.005
N*
Homeotropic
Planar
the use of Ni filtered Cu K
ground radiation in addition to the Cu K
a
radiation, which contains a white back-
peak. No correction for
a
BPII
Iso
this white radiation, which broadens the diffraction peaks consid-
erably, is made here. Hence the experimental values of correlation
lengths as obtained above are somewhat smaller than the theoret-
ically expected values.
SmA*
Cr.
TGBA
30
40
50
60
70
80
90
T / oC
3.4. Dielectric spectroscopy
Fig. 5. Temperature dependence of the transmitted intensity obtained on samples
in planar alignment (open circles) and homeotropic alignment (open squares).
Temperature dependence of the real part of complex permittiv-
ity measured on cooling at a frequency of 160 Hz within the range
of all detected mesophases is shown in Fig. 12. As no polar phase
was detected for this chiral LC material, the only contribution of
the soft mode in the paraelectric SmAꢀ phase could be detected.
It results in a pronounced increase of the real part of complex
permittivity on cooling below the TGBA–SmAꢀ phase transition. A
peak at the low temperature border of the SmAꢀ phase is related
to pre-crystallisation phenomena.
the higher ordered phase are found to be much higher than those
for the lower ordered phases.
The values of the transverse correlation lengths is about 50 Å in
SmAꢀ phase. In the vicinity of the SmAꢀ–TGBA phase transition,
there is a rapid decrease of correlation length on heating from
the SmAꢀ phase to the TGBA phase. At the TGBA–Nꢀ phase transition
there appears to be a divergence of n\ near the TGBA–Nꢀ phase
In order to study the effect of the molecular structure on meso-
morphic properties, the compound studied in this work has been

124
B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
Fig. 6. X-ray diffraction photographs obtained on the unaligned sample in (a) BPII phase (85.5 °C); (b) TGBA phase (70 °C) and (c) SmAꢀ phase (50 °C).
TGBA
SmA*
N*
5.3
5.2
5.1
5.0
4.9
BPII
SmA*(55oC)
TGBA(70oC)
N*(84oC)
40
50
60
T / oC
70
80
90
BPII(85.5oC)
Fig. 9. Temperature dependence of the average intermolecular distance D.
5
10
15
2θ /deg.
20
25
10000
Fig. 7. X-ray diffraction profiles at indicated temperatures with nearly equal
SmA*
N*
exposure time.
TGBA
8000
BPII
40
6000
4000
2000
SmA*
N*
TGBA
38
BPII
36
34
32
30
28
40
50
60
T / oC
70
80
90
Fig. 10. Temperature dependence of the X-ray intensity of the inner ring (with
nearly same exposure time).
40
50
60
T / oC
70
80
90
by NO2 group laterally substituted on phenyl ring close to the chiral
centre [27]. In case of double lateral substitution, namely when the
methyl group is placed far from the chiral centre and the NO2 group
is placed close to the chiral centre, no liquid crystalline behaviour
can be detected [27]. However, the lateral substitution by the single
methyl group on phenyl ring far from the chiral centre retains the
cholesteric phase; the clearing point for that compound is about
40 K lower than that obtained for compound studied in the present
work. Liquid crystalline material containing the chiral 2-alkoxypro-
pionate unit (connected to the molecular core by ester group)
instead of the chiral lactate unit (connected to the molecular core
by ether group) possess a broad range of the cholesteric phase
and the ferroelectric SmCꢀ phase [28]. However, the clearing point
Fig. 8. Temperature dependence of the layer thickness d.
compared with compounds having slightly different molecular
structure. In particular the effect of: (i) the influence of the chains
length, (ii) lateral substitutions by various groups in different posi-
tions as well as (iii) the effect of the type of the group, which
connect the chiral molecular chain, have been investigated. If the
length of the non-chiral chain is increased, the tilted ferroelectric
SmCꢀ phase of about 20 K broad down to room temperature has
been found [21]. The lateral substitution by two methyl groups
[26] on the phenyl ring far from the chiral centre completely sup-
presses the mesomorphic properties. The same effect is reached

B. Das et al. / Journal of Molecular Structure 1013 (2012) 119–125
125
temperature dependence of the scattered X-ray intensities. Similar
behaviour is also observed in the d values obtained for this
compound.
The in-plane transverse correlation length n\ as well as the lon-
gitudinal correlation length n|| are found to be much higher for
higher ordered phase than those for the lower order phase. The
n\ values diverge near the TGBA–Nꢀ phase transition indicating
second order phase transition.
48
42
36
30
24
BPII
N*
TGBA
300
200
100
SmA*
Acknowledgements
40
50
60
T / oC
70
80
90
This work is supported by Projects: GA ASCR IAA100100911,
CSF P204/11/0723, RFASI 02.740.11.5166 and CSF 202/09/0047.
We would like to express our gratitude to Dr. U. Baumeister for ac-
cess to the 2D area X-ray detector that allows us to record the dif-
fraction patterns. We are also very thankful to Dr. M. Prehm for
assistance in recording the X-ray diffraction images.
Fig. 11. Temperature dependence of the longitudinal, n|| (open circles) and the
transverse, n\ (close squares) correlation lengths within the mesophases.
References
BPII
6
5
4
3
Cr.
[1] J.P.F. Lagerwall, F. Giesselmann, ChemPhysChem 7 (2006) 20.
[2] P. de Gennes, J. Prost, The Physics of Liquid Crystals, Clarendon Press, Oxford,
1999.
[3] S.T. Lagerwall, Ferroelectric and Antiferroelectric Liquid Crystals, Wiley-VCH
Verlag GmbH, Weinheim, 1999.
[4] H. Taniguchi, M. Ozaki, K. Yoshino, K. Satoh, N. Yamasaki, Ferroelectrics 77
(1988) 137.
[5] S.A. Pakhomov, M. Kašpar, V. Hamplová, A.M. Bubnov, H. Sverenyák, M.
Glogarová, I. Stibor, Ferroelectrics 212 (1998) 341.
[6] A. Bubnov, V. Hamplová, M. Kašpar, M. Glogarová, P. Vank, Ferroelectrics 243
(2000) 27.
[7] V. Hamplová, A. Bubnov, M. Kašpar, V. Novotná, M. Glogarová, Liq. Cryst. 30
(2003) 493.
[8] V. Hamplová, A. Bubnov, M. Kašpar, V. Novotná, D. Pociecha, M. Glogarová, Liq.
Cryst. 30 (2003) 627.
SmA*
TGBA
N*
Iso
30
40
50
60
70
80
90
T / oC
[9] V. Hamplová, A. Bubnov, M. Kašpar, V. Novotná, Y. Lhotáková, M. Glogarová,
Liq. Cryst. 30 (2003) 1463.
[10] M. Kašpar, A. Bubnov, V. Hamplová, S. Pirkl, M. Glogarová, Liq. Cryst. 31 (2004)
821.
Fig. 12. Temperature dependence of the real part of complex permittivity
measured on cooling at a frequency of 160 Hz.
[11] A. Bubnov, M. Kašpar, V. Hamplová, M. Glogarová, S. Samaritani, G. Galli, G.
Andersson, L. Komitov, Liq. Cryst. 33 (2006) 559.
[12] D. Catalano, V. Domenici, A. Marini, C.A. Veracini, A. Bubnov, M. Glogarová, J.
Phys. Chem. B 110 (2006) 16459.
is evidently higher than that for the material studied in the present
work; the difference is more than 40 K [28].
[13] W.-L. Tsai, S.-W. Yen, M.J. Hsie, H.-C. Lee, C.M. Fu, Liq. Cryst. 29 (2002) 251.
[14] W.L. Tsai, T.Ch. Lu, H.W. Liu, M.Y. Tsai, C.M. Fu, Liq. Cryst. 27 (2000) 1389.
[15] M. Kašpar, P. Bilková, A. Bubnov, V. Hamplová, V. Novotná, M. Glogarová, K.
4. Summary of the results and conclusions
ˇ
Knizek, D. Pociecha, Liq. Cryst. 35 (2008) 641.
[16] V. Novotná, V. Hamplová, A. Bubnov, M. Kašpar, M. Glogarová, N. Kapernaum,
S. Bezner, F. Giesselmann, J. Mater. Chem. 19 (2009) 3992.
[17] N. Podoliak, V. Novotná, M. Glogarová, V. Hamplová, M. Kašpar, A. Bubnov, N.
Kapernaum, F. Giesselmann, Phase Transitions 83 (2010) 1026.
[18] V. Novotná, V. Hamplová, M. Kašpar, N. Podoliak, A. Bubnov, M. Glogarová, D.
Nonnenmacher, F. Giesselmann, Liq. Cryst. 38 (2011) 649.
[19] A. Bubnov, V. Novotná, V. Hamplová, M. Kašpar, M. Glogarová, J. Mol. Struct.
892 (2008) 151.
The mesomorphic and structural properties of a liquid crystal-
line material with chiral lactate group possessing a blue phase,
cholesteric, TGBA and SmAꢀ phases has been studied by different
experimental techniques.
The layer spacing (d) in the SmAꢀ phase, determined from X-ray
diffraction measurements, is slightly temperature dependent.
Within the TGBA phase, the d/l ratio indicates the existence of
monolayer SmA blocks and identifies the TGB phase of this com-
pound to be composed of blocks of SmA layers.
[20] A. Bubnov, S. Pakhomov, M. Kašpar, V. Hamplová, M. Glogarová, Mol. Cryst. Liq.
Cryst. 328 (1999) 317.
[21] M. Garic´, A. Bubnov, V. Novotná, M. Kašpar, V. Hamplová, D.Z. Obadovic, M.
Glogarová, Liq. Cryst. 32 (2005) 565.
[22] G. Sarkar, M.K. Das, R. Paul, B. Das, W. Weissflog, Phase Transitions 82 (2009)
433.
[23] G. Sarkar, B. Das, M.K. Das, U. Baumaister, W. Weissflog, Mol. Cryst. Liq. Cryst.
540 (2011) 188.
Definite discontinuities in the X-ray scattering are observed at
the Nꢀ–TGBA phase boundary. The increased intensities at this
phase transition mark the onset of the long range smectic ordering
of the TGBA phase. A rapid increase in the X-ray scattering intensi-
ties is again observed at the TGBA–SmAꢀ phase transition, perhaps
due to the presence of strong Smectic Aꢀ fluctuations. Since, the
transition from the Nꢀ phase to the Sm Aꢀ phase in this compound
is facilitated via the formation of the TGBA phase, both the appear-
ance of the smectic blocks at the Nꢀ–TGBA phase transition as well
as the disappearance of the helical twist of the cholesteric director
at the TGBA–SmAꢀ phase boundary is clearly reflected from the
[24] A. Chakraborty, M.K. Das, B. Das, S. Findeisen-Tandel, M.G. Tamba, U.
Baumeister, H. Kresse, W. Weissflog, Liq. Cryst. 38 (2011) 1085.
[25] D.S. Shankar Rao, S. Krishna Prasad, V.N. Raja, C.V. Yelamaggad, S. Anitha
Nagamani, Phy. Rev. Lett. 87 (2001) 085504.
ˇ
[26] D.Z. Obadovic´, A. Vajda, M. Garic´, A. Bubnov, V. Hamplová, M. Kašpar, K. Fodor-
Csorba, J. Therm. Anal. Calorim. 82 (2005) 519.
[27] M. Kašpar, V. Hamplová, A. Bubnov, V. Novotná, unpublished results of the
group.
[28] M. Kašpar, V. Hamplová, S.A. Pakhomov, I. Stibor, H. Sverenyák, A.M. Bubnov,
M. Glogarová, P. Vank, Liq. Cryst. 22 (1997) 557.