Dielectric and optical studies in smectic C of a novel hydrogen bonded liquid crystal homologous series

Article abstract of DOI:10.1080/15421406.2012.687673

A novel hydrogen bonded liquid crystalline series comprising of p-n alkyloxy benzoic acids is isolated. This series include seven complexes in which hydrogen bond is formed between undecyloxy benzoic acid and various homologues of benzoic acid varying from pentyl to dodecyloxy carbon number. All the homologues of the present series show rich mesomorphism exhibiting orthogonal and tilted phases. The formation of the hydrogen bond is confirmed by Fourier transform infrared spectroscopy studies. Transition temperatures and corresponding enthalpy values along with enantiotropic and monotropic transitions are elucidated from differential scanning calorimetry thermograms. Polarizing optical microscopy revealed various phases in the form of textures. An interesting observation is the identification of a new smectic ordering labeled as smectic X which is sandwiched between traditional nematic and convectional smectic C phases. Dielectric relaxations in smectic C phase of three homologues have been analyzed and the activation energy is calculated from respective Arrhenius plots. Taylor and Francis Group, LLC.

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Dielectric and Optical Studies in Smectic
C of A Novel Hydrogen Bonded Liquid
Crystal Homologous Series
N. Pongali Sathya Prabu a & M. L. N Madhu Mohan a
a Liquid Crystal Research Laboratory (LCRL), Bannari Amman
Institute of Technology, Sathyamangalam, Tamil Nadu, India
Version of record first published: 30 Jul 2012.
To cite this article: N. Pongali Sathya Prabu & M. L. N Madhu Mohan (2012): Dielectric and Optical
Studies in Smectic C of A Novel Hydrogen Bonded Liquid Crystal Homologous Series, Molecular Crystals
and Liquid Crystals, 562:1, 177-190
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Mol. Cryst. Liq. Cryst., Vol. 562: pp. 177–190, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.687673
Dielectric and Optical Studies in Smectic C
of A Novel Hydrogen Bonded Liquid Crystal
Homologous Series
N. PONGALI SATHYA PRABU AND M. L. N MADHU
MOHAN∗
Liquid Crystal Research Laboratory (LCRL), Bannari Amman Institute
of Technology, Sathyamangalam, Tamil Nadu, India
A novel hydrogen bonded liquid crystalline series comprising of p-n alkyloxy benzoic
acids is isolated. This series include seven complexes in which hydrogen bond is formed
between undecyloxy benzoic acid and various homologues of benzoic acid varying from
pentyl to dodecyloxy carbon number. All the homologues of the present series show rich
mesomorphism exhibiting orthogonal and tilted phases. The formation of the hydrogen
bond is confirmed by Fourier transform infrared spectroscopy studies. Transition tem-
peratures and corresponding enthalpy values along with enantiotropic and monotropic
transitions are elucidated from differential scanning calorimetry thermograms. Polar-
izing optical microscopy revealed various phases in the form of textures. An interesting
observation is the identification of a new smectic ordering labeled as smectic X which
is sandwiched between traditional nematic and convectional smectic C phases. Dielec-
tric relaxations in smectic C phase of three homologues have been analyzed and the
activation energy is calculated from respective Arrhenius plots.
Keywords Arrhenius plots; dielectric relaxations; DSC; smectic X; tilted phases
1. Introduction
Liquid crystals exhibiting the intermediate phases during their phase transitions have both
the properties of conventional solid and isotropic liquid which makes these systems unique
and gives rise to many interesting properties leading to the engineering application aspects
[1]. Molecular orientation and the self-assembly systems form the basic requirements for
exhibiting these interesting properties. Hydrogen bonding is one of the principal inter-
molecular forces which helps in construction of such supra molecular structures and is
the key interactions for the chemical and biological processes in nature [2–10]. Recently,
a number of supra molecular mesogenic materials have been obtained by molecular self-
assembly through intermolecular hydrogen bonding [11–21]. For molecular aggregates,
hydrogen bonding plays an important role in the association of the molecules. Kato and his
group prepared a variety of liquid crystals induced by this intermolecular hydrogen bonding
between pyridyl moieties which are proton acceptors and carboxylic acid groups which are
∗Address correspondence to M. L. N Madhu Mohan, Liquid Crystal Research Laboratory
(LCRL), Bannari Amman Institute of Technology, Sathyamangalam 638 401, Tamil Nadu, India.
Tel.: +91 9442437480; Fax: +91 4295 223775. E-mail: mln.madhu@gmail.com
177

178
N. Pongali Sathya Prabu and M. L. N Madhu Mohan
proton donors [4]. Many liquid crystal systems like molecular liquid crystals [22–26], poly-
mer liquid crystals [27–31], ferroelectric liquid crystals [32,33], and even room temperature
liquid crystals have been prepared [8]. Single bond [34–36], double bond [37–40], and even
multiple bond [41,42] hydrogen-bonded liquid crystals are synthesized and reported.
The central theme of the aimed research work involves in design, synthesis, and char-
acterization of eight homologous series of hydrogen bonded liquid crystals (HBLC) formed
between p-n-alkyloxy benzoic acid (nBAO) and p-n-alkyloxy benzoic acids (mBAO) re-
ferred as nBAO+mBAO, where m varies from 5 to 12. These eight series can be re-
ferred as 5BAO+mBAO, 6BAO+mBAO, 7BAO+mBAO, 8BAO+mBAO, 9BAO+mBAO,
10BAO+mBAO, 11BAO+mBAO, and 12BAO+mBAO which give rise to 56 different
hydrogen-bonded complexes. In this paper, systematic study of the mesogenic properties
exhibited by seven complexes of 11BAO+mBAO homologous series are discussed. These
system forms the complimentary bond as they themselves behaves as donors and acceptors.
2. Experimental
Optical textural observations were made with a Nikon polarizing optical microscope (POM)
equipped with Nikon digital CCD camera system with 5 megapixels and 2560 × 1920 pixel
resolutions (Nikon, Tokyo, Japan). The liquid crystalline textures were analyzed and stored
with the aid of ACT-2U imaging software system. The temperature control of the liquid
crystal cell was equipped by Instec HCS402-STC 200 temperature controller (Instec, Boul-
der, Colorado) to a temperature resolution of 0.1◦C. This unit was interfaced to computer
by IEEE–STC 200 to control and monitor the temperature. The liquid crystal sample was
filled by capillary action in its isotropic state into a commercially available (Instec, USA)
polyamide buffed cell with 4 µm spacer. Optical extinction technique [40] was used for
determination of tilt angle. Transition temperatures and corresponding enthalpy values were
obtained by differential scanning calorimetry (DSC) (Shimadzu DSC-60, Kyoto, Japan).
Fourier transform infrared spectroscopy (FTIR) spectra was recorded (ABB FTIR MB3000,
Quebec, Canada)) and analyzed with the MB3000 software. The p-n-undecyloxy benzoic
acid (11BAO) and p-n-alkyloxy benzoic acids (mBAO, where m = 5 to 12) were supplied
by Sigma Aldrich (Steinheim, Germany) and all the solvents were of high-performance
liquid chromatography (HPLC) grade.
2.1 Synthesis of HBLC
All the inter hydrogen-bonded complexes examined in the present study are prepared by
mixing in 1:1 molar ratio undecyloxy benzoic acid with various alkyloxy benzoic acids in
dimethyl formamide (DMF) and reprecipitating after the evaporation as described in the
reported literature [43–45]. Molecular structure of the present homologous series of p-n-
undecyloxy benzoic acid (11BAO) with p-n-alkyloxy benzoic acids (mBAO, Where m =
5 to 12) is depicted in the Fig. 1 where m represents the alkyloxy carbon number.
OH
O
O
C11H23
O
C
OCnH2n+1
C
OH
Figure 1. Molecular structure of undecyloxy benzoic acid and alkyloxy benzoic acid hydrogen
bonded complexes.

Dielectric and Optical Studies in Smectic C
3. Results and Discussion
179
All the hydrogen-bonded complexes isolated under the present investigation are white
crystalline solids and are stable at room temperature (30◦C). They are insoluble in water
and sparingly soluble in common organic solvents such as methanol, ethanol, benzene, and
dichloro methane. However, they show a high degree of solubility in coordinating solvents
like dimethyl sulfoxide (DMSO), DMF, and pyridine. All these mesogens melt at specific
temperatures below ∼88.4◦C (Table 1). They show high thermal and chemical stability
when subjected to repeated thermal scans performed during POM and DSC studies.
3.1 Phase Identification
The observed phase variants, transition temperatures, and corresponding enthalpy values
obtained by DSC in the cooling and heating cycles for the 11BAO+mBAO complexes are
presented in Table 1. These data are in concurrence with POM data.
3.2 Phases Exhibited by 11BAO+nBAO Homologous Series
The mesogens of the p-n-undecyloxy benzoic acid (11BAO) with p-n-alkyloxy benzoic
acids (mBAO, where m = 5 to 12) designated as 11BAO+mBAO homologous series are
found to exhibit characteristic textures [46], viz., nematic (N) (droplets texture, Plate 1),
smectic X (worm like texture, Plate 2), smectic C (schlieren texture, Plate 3), and smectic
F (chequered board texture, Plate 4), respectively. The general phase sequence of various
homologues of 11BAO+mBAO series in cooling and heating runs can be shown as:
Iso ꢀ N → Sm X → Sm C ꢀ Crystal (11BAO+5BAO)
Iso ꢀ N ꢀ Sm C ꢀ Crystal (11BAO + 6BAO, 7BAO and 8BAO)
Iso ꢀ N → Sm C ꢀ Sm F ꢀ Crystal (11BAO+9BAO)
Iso ꢀ N ꢀ Sm C ꢀ Crystal (11BAO+10BAO)
Iso ꢀ N → Sm X ꢀ Sm C ꢀ Crystal (11BAO+12BAO)
Monotropic and enantiotropic transitions are depicted as single and double arrows,
respectively.
3.3 FTIR Study
FTIR spectra for all the HBLC complexes are recorded in the solid state (KBr) at room
temperature. As a representative case, Fig. 2 illustrates the FTIR spectra of 11BAO+12BAO
in solid state at room temperature which is discussed elaborately. It is reported [47,48] that
in the alkyloxy benzoic acids, carboxylic acid exists in monomeric form and the stretching
vibration of C O is observed at 1760 cm−1. Further it is known [48] that when a hydrogen
bond is formed between carboxylic acids it results in lowering of the carbonyl frequency
which has been detected in the present hydrogen-bonded complexes. A noteworthy feature
in the spectrum of the 11BAO+12BAO is the appearance of sharp peak at 1674 cm−1
which clearly suggests the dimmer formation in particular the carbonyl group vibration
[49–51]. A carboxylic acid existing in monomeric form in dilute solution absorbs at about
1760cm−1 because of the electron withdrawing effect. However, acids in concentration
solution or in solid state tend to dimerize through hydrogen bonding. It is reported [48]
that this dimerization weakens the C O bond and lowers the stretching force constant K,

180

Dielectric and Optical Studies in Smectic C
181
Plates 1–4. 1. Nematic droplets texture of nematic phase obtained in 11BAO+7BAO com-
plex recorded at 125.4◦C. 2. Worm-like texture of smectic X phase obtained in 11BAO+5BAO
complex recorded at 120.4◦C. 3. Schlieren texture of smectic C phase obtained in 11BAO+
8BAO complex recorded at 105.9◦C. 4. Chequered board texture of smectic F obtained in 11BAO+
9BAO complex recorded at 110.7◦C. (All plates are recorded under crossed polarizer’s with 5 ×
magnification)
resulting in a lowering of the carbonyl frequency of saturated acids to ∼1710 cm−1. This
result concurs with the reported data of Kato et al. [47]. Hence, in the present complexes
the formation of H bonding is established by FTIR. A similar trend of result is followed in
all the synthesized hydrogen-bonded complexes.
3.4 DSC Studies
DSC thermograms are recorded in heating and cooling cycle. The sample is heated with
a scan rate of 10◦C min–1 and held at its isotropic temperature for 2 min so as to attain
thermal stability. The cooling run is performed with the same scan rate of 10◦C min–1.
The respective equilibrium transition temperatures and corresponding enthalpy values of
the mesogens of the homologous series are listed separately in Table 1. POM studies also
concur with the DSC transition temperatures. The entire DSC exothermic thermograms of
the synthesized 11BAO+mBAO complexes are depicted in Fig. 3. It is plotted for the DSC

182
N. Pongali Sathya Prabu and M. L. N Madhu Mohan
Figure 2. FTIR spectra of 11BAO+12BAO complex.
cooling thermograms by assigning the temperature variation along x-axis and the corre-
sponding enthalpy value (ꢀH) along y-axis. It is inferred from the DSC thermograms (Fig. 3)
that as the alkyloxy chain length increases the orthogonal nematic ordering is quenched
by the tilted smectic ordering C which paved way for its higher thermal span. Moreover,
from the enthalpy values obtained from the cooling run of the DSC thermograms, the phase
transitions from isotropic to nematic, nematic to smectic C, and smectic C to crystal is
categorized as first-order transitions. In the complexes 11BAO+9BAO, 11BAO+10BAO,
11BAO+mBAO
DSC cooling cycle
35
30
25
20
15
10
5
N
Iso.
C
n=12
K
1
K
K
N
Iso.
K
C
n=10
n=9
1
N
N
Iso.
Iso.
C
F
K
K
1
n=8
C
K
N
Iso.
Iso.
n=7
n=6
n=5
C
K
N
C
K
N
Iso.
K
0
40
60
80
Temperature (°C)
Figure 3. DSC thermogram of 11BAO+mBAO series in cooling run.
100
120
140

Dielectric and Optical Studies in Smectic C
183
11BAO + mBAO
Isotropic
140
X
N
X
120
C
C
100
80
F
C
Crystal
60
5
6
7
8
9
10
11
12
Alkyloxy carbon number
Figure 4. Phase diagram of 11BAO+mBAO homologous series.
and 11BAO+12BAO in the cooling run of the DSC, a transition is noticed after crystal-
lization which is classified as solid-to-solid transition and labeled as K1 (crystal-to-crystal
transition).
3.5 Phase Diagram of Pure p-n-alkyloxy Benzoic Acid
The phase diagram of pure 11BAO is reported [52,53] to compose of two phases namely,
nematic and smectic C.
3.5.1 Phase Diagram of 11BAO+mBAO. Phase diagram of p-n-undecyloxy benzoic acid
and p-n-alkyloxy benzoic acids (11BAO+mBAO) homologues series is depicted in Fig. 4.
The following points can be elucidated from Fig. 4:
• The phase diagram consists of four phases, viz. nematic, smectic X, smectic C, and
smectic F.
• It is interesting to note that smectic X phase is observed in the first (11BAO+5BAO)
and last members (11BAO+12BAO) of the homologous series with a narrow thermal
span.
• Nematic and smectic C phases are observed in all the alkyloxy carbon numbers.
Quenching of the nematic phase by smectic C is observed as the carbon chain length
increases.
• A wide range of thermal span of smectic C is observed in the series.
• A new smectic ordering labeled as Sm X is observed and characterized. In an
identical homologous series, a similar phase has been characterized earlier by us
[54,55,56] using different techniques.
• It is surprising to note that smectic F, the highly oriented phase is observed only in
the 11BAO+9BAO complex.
• The over all mesogenic thermal range possessed by individual complexes of the
series has decreased with the increment in carbon number.
• Odd even effect is not observed at isotropic to nematic interface either in transition
temperatures or in corresponding enthalpy values.

184
N. Pongali Sathya Prabu and M. L. N Madhu Mohan
Smectic C
20
15
11BAO+5BAO
11BAO+6BAO
11BAO+7BAO
10
11BAO+8BAO
11BAO+9BAO
11BAO+10BAO
5
11BAO+12BAO
0
0
0
2
4
6
8
10
(T-T ) /°C
c
Figure 5. Temperature variation of tilt angle in smectic C phase for 11BAO+mBAO series, where
m = pentyloxy to dodecyloxy benzoic acids.
4. Optical Tilt Angle Measurement
The optical tilt angle has been experimentally measured by optical extinction method [40]
in smectic C phase for all the members of the present 11BAO+mBAO homologous series.
Figure 5 depicts such variation of optical tilt angle with temperature for 11BAO+mBAO
(where m = 5 to 12) series. In Fig. 5, the theoretical fit obtained from the mean field theory
is denoted by the solid line. It is observed from the figure that the tilt angle increases with
decreasing temperature and attains a saturation value. These large magnitudes of the tilt
angle are attributed to the direction of the soft covalent hydrogen bond interaction which
spreads along molecular long axis with finite inclination [57]. On examining Fig. 5, it
can be inferred that in the lower homologues of 11BAO+mBAO (where, m = 5 to 7) the
magnitude of saturated tilt angle is observed to be ∼14◦ while in the higher homologues
(m = 8 to 12) the magnitude of saturated tilt angle is observed to be ∼18◦. This segregation
of the complexes based on the magnitude of the tilt angle measured happens to be due to
the effective increase in the thermal span of the smectic C phase on suppressing the nematic
phase as the alkyloxy chain length is increased. Increase in the carbon number reciprocates
an increase in the saturation value of the tilt angle measurement.
Tilt angle is a primary-order parameter [58] and the temperature variation is estimated
by fitting the observed data of θ(T) to the relation
θ(T)α(TC − T)β.
(1)
The critical exponent β value estimated by fitting the data of θ(T) to the above equa-
tion (1) is found to be 0.50 to agree with the mean field prediction [1,59]. The solid lines in
the Fig. 5 depict the fitted data for various mesogens. Further, the agreement of magnitude
of β (0.5) with mean field value (0.5) infers the long-range interaction of transverse dipole
moment for the stabilization of tilted smectic C phase.
5. Dielectric Studies
Empty cell is calibrated with temperature (30◦C–200◦C) and frequency (5Hz–13 MHz) by
a known substance (benzene) to calculate the leads capacitance.

Dielectric and Optical Studies in Smectic C
185
11BAO+6BAO
0.0585
0.0580
0.0575
0.0570
Smectic C
0
91.1 C
86.2
81.2
76.2
71.4
66.4
61.4
110
112
114
'/pF
116
118
ε
Figure 6. Dispersion curves obtained for the 11BAO+6BAO complex in its smectic C phase for
various temperatures.
5.1 Dielectric Relaxations
Dielectric dispersion, i.e., frequency variation of dielectric loss exhibited by 11BAO+
6BAO, 11BAO+7BAO, and 11BAO+8BAO are studied at different temperatures in smectic
C phase in the frequency range of 5–13 MHz. An impedance analyzer (Agilent 4192A LF,
Santa Clara, California) is operated with 1VP-P oscillating signal with zero-bias field.
Relative permittivity εrꢀ (ω) and dielectric loss εꢀꢀ (ω) are calculated by the following
equations
∗εrꢀ (ω) = εrꢀ (ω) − jεꢀꢀ (ω),
εrꢀ (ω) = [CLC − Cleads]/[Cempty − Cleads],
∗εrꢀ (ω) = Tanδ (ω)∗εr (ω).
To detect the possible relaxation in the 11BAO+nBAO complexes, the mesogens are
scanned in the frequency range of 5–13 MHz at different temperatures in the smectic C
phase of the corresponding complex. In all the complexes the relaxation frequency (fr)
decreases with lowering temperature which is suggestive of an Arrhenius behavior [60–62]
as it reflects the collective response. Further, the magnitude of the dielectric loss is shifted
and is not suppressed by the temperature the slope of the log of relaxation frequency to
inverse of temperature, referred as Arrhenius plot gives the activation energy of the phase.
The high value of the activation energies in complexes is attributed to the steric hindrance
of the alkyloxy benzoic acid moiety.
The corresponding dispersion curves and Arrhenius plots for all the complexes studied
ꢀꢀ
are illustrated in Figs 6–9 and they appear to be asymmetric about ε . Such a asymmetric
max
non-Debbie’s type of off-centered dispersion is studied by Cole–Davidson theory [60–62]
given by
εꢀꢀ (ω) = {ε∞ − [(ꢀε)]/[1 + (jωτ)1−α},
where
ꢀε = (εo – ε ) = the dielectric increment (strength),
∞
ω = 2пf (where f is the frequency of AC signal),

186
N. Pongali Sathya Prabu and M. L. N Madhu Mohan
0
Smectic C
0.072
0.069
0.066
0.063
11BAO+7BAO
C
103
100
97
94
91
88
85
82
79
76
73
70
114
117
120
123
/pF
126
129
ε'
Figure 7. Dispersion curves obtained for the 11BAO+7BAO complex in its smectic C phase for
various temperatures.
T = relaxation time, i.e., 1 fr–1
,
α = the distribution parameter (or degrees of freedom) to estimate the influence of envi-
ronment of dipoles and its fixation in the molecular frame during the reorientation to
the field.
5.1.1 Dielectric Relaxations in 11BAO+6BAO. The dielectric relaxations in 11BAO+
6BAO complex have been investigated in the entire thermal span of smectic C phase
(99.5◦C to 58.5◦C) at seven temperatures namely 91.1◦C, 86.2◦C, 81.2◦C, 76.2◦C, 71.4◦C,
66.4◦C, and 61.4◦C, respectively, which are decremented in equal steps of 5◦C.
The shift of the relaxation frequency (fr) to lower side with decrease in temperature can
be noticed from Fig. 6 and Table 2. The relaxation frequency shifted from 225 KHz to 210
KHz in a temperature span of 30◦C. Arrhenius plots are drawn (Fig. 9) and the activation
energy corresponding to smectic C is calculated to be 0.95 eV. Table 2 presents the studied
temperatures, the magnitudes of relaxation frequency, dielectric loss, and corresponding
o
11BAO+8BAO
Smectic C
C
0.076
0.075
0.074
0.073
0.072
109.1
107.1
105.1
103.1
101.1
99.1
97.1
117
120
123
126
ε'/pF
Figure 8. Dispersion curves obtained for the 11BAO+8BAO complex in its smectic C phase for
various temperatures.

Dielectric and Optical Studies in Smectic C
187
2.35
2.30
2.25
2.20
11BAO+6BAO
11BAO+7BAO
11BAO+8BAO
2.15
0.0026 0.0027 0.0028 0.0029 0.0030
-1
(1/T K )
Figure 9. Arrhenius plots for 11BAO+mBAO complexes (m = 6 to 8).
Table 2. Values of relaxation frequency and corresponding temperature along with activa-
tion energy for various complexes
Activation
energy (eV)
Complex
T (◦C)
fr (KHz)
τ (µs)
εꢀꢀ max
α (rad)
11BAO+6BAO
91.1
86.2
81.2
76.2
71.4
66.4
61.4
103
100
97
94
91
88
85
82
79
76
73
225
220
218
216
214
212
210
180
178
176
174
172
170
168
166
164
162
160
158
200
190
180
170
160
150
140
4.44
4.54
4.58
4.62
4.67
4.71
4.76
5.55
5.61
5.68
5.74
5.81
5.88
5.95
6.02
6.09
6.17
6.25
6.32
5
0.0583
0.0583
0.0582
0.0581
0.0581
0.0581
0.0580
0.0719
0.0718
0.0717
0.0716
0.0715
0.0714
0.0713
0.0712
0.0710
0.0708
0.0707
0.0706
0.0758
0.0757
0.0756
0.0755
0.0751
0.0750
0.0747
0.8198
0.7152
0.628
0.95
0.5931
0.5582
0.5233
0.3663
0.2965
0.3663
0.5233
0.5407
0.5582
0.6105
0.6628
0.6977
0.7326
0.7501
0.8024
0.8198
0.8547
0.8024
0.7850
0.4361
0.4136
0.4012
0.3837
11BAO+7BAO
0.99
70
11BAO+8BAO
109.1
107.1
105.1
103.1
101.1
99.1
97.1
0.99
5.26
5.55
5.88
6.25
6.66
7.14

188
N. Pongali Sathya Prabu and M. L. N Madhu Mohan
relaxation time. The distribution parameter α has been calculated for each relaxation process
and it is noticed that the magnitude of α decreases as the temperature is decreased.
5.1.2 Dielectric Relaxations in 11BAO+7BAO. The dielectric relaxations in 11BAO+
7BAO complex have been investigated in the entire thermal span of smectic C phase
(107.9◦C to 57.9◦C) at 12 temperatures namely 103◦C, 100◦C, 97◦C, 94◦C, 91◦C, 88◦C,
85◦C, 82◦C, 79◦C, 76◦C, 73◦C, and 70◦C, respectively, which are decremented in equal
steps of 3◦C. The shift of the relaxation frequency (fr) to lower side with decrease in
temperature can be noticed from Fig. 7 and Table 2. The relaxation frequency shifted from
180 KHz to 158 KHz in a temperature span of 33◦C. Arrhenius plots are drawn (Fig. 9)
and the activation energy corresponding to smectic C is calculated to be 0.99 eV. Table 2
presents the studied temperatures, the magnitudes of relaxation frequency, dielectric loss,
and corresponding relaxation time. The distribution parameter α has been calculated for
each relaxation process and it is noticed that the magnitude of α increases as the temperature
is decreased.
5.1.3 Dielectric Relaxations in 11BAO+8BAO. The dielectric relaxations in 11BAO+
8BAO complex have been investigated in the entire thermal span of smectic C phase
(115.9◦C to 63.5◦C) at seven temperatures namely 109.1◦C, 107.1◦C, 105.1◦C, 103.1◦C,
101.1◦C, 99.1◦C, and 97.1◦C, respectively, which are decremented in equal steps of 2◦C.
The shift of the relaxation frequency (fr) to lower side with decrease in temperature can be
noticed from Fig. 8 and Table 2. The relaxation frequency shifted from 200 KHz to 140 KHz
in a temperature span of 12◦C. Arrhenius plots are drawn (Fig. 9) and the activation energy
corresponding to smectic C is calculated to be 0.99 eV. Table 2 presents the temperatures
studied the magnitudes of relaxation frequency, dielectric loss, and corresponding relaxation
time. The distribution parameter α has been calculated for each relaxation process and it is
noticed that the magnitude of α decreases as the temperature is decreased.
Acknowledgments
The graceful blessings showered by the goddesses Bannari Amman are gratefully acknowl-
edged. Infrastructural support provided by Bannari Amman Institute of Technology is also
gratefully acknowledged.
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