Synthesis, preparation, and characterization of liquid crystal/organo-montmorillonite nanocomposites

Article abstract of DOI:10.1080/15421406.2014.927550

A new chiral calamitic liquid crystal 4′-((S)-3,7-dimethyloctyloxy)phenyl 4-(10-undecen-1-yloxy)benzoate (DOPUB) has been synthesized and characterized by spectroscopic methods (¹H-NMR and ¹³C-NMR). The focus is on the preparation of the nanocomposites of new chiral calamitic liquid crystal DOPUB/Organo-montmorillonite clay (OMMT) by solution intercalation method addition with OMMT contents 2.5, 5, and 7.5 wt% and determination of the morphology, thermal behavior, and crystalline properties of liquid crystal DOPUB/OMMT. Montmorillonite (MMT) modified by cationic surfactant cetyltrimethylammonium bromide (CTAB) for increasing the interaction of clay with DOPUB liquid crystal. The characterization of clay minerals and nanocomposites was investigated by X-ray diffraction. The mesomorphic behavior of liquid crystal (DOPUB) and the nanocomposites was investigated by differential scanning calorimetry (DSC) and optical polarizing microscopy (PM).

Full text of DOI:10.1080/15421406.2014.927550

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Synthesis, Preparation, and
Characterization of Liquid Crystal/
Organo-Montmorillonite Nanocomposites
ab
a
a
a
Serap Mutlu Yanic , Dilek Guzeller , Hale Ocak , Fatih Cakar ,
a
a
a
Ismail Erol , Ozlem Cankurtaran & Belkis Bilgin Eran
a
Yildiz Technical University, Department of Chemistry, Davutpasa
Campus, Istanbul, Turkey
b
Gedik University, Chemistry Technology Programme, Pendik,
Istanbul, Turkey
Published online: 26 Feb 2015.
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To cite this article: Serap Mutlu Yanic, Dilek Guzeller, Hale Ocak, Fatih Cakar, Ismail Erol, Ozlem
Cankurtaran & Belkis Bilgin Eran (2015) Synthesis, Preparation, and Characterization of Liquid
Crystal/Organo-Montmorillonite Nanocomposites, Molecular Crystals and Liquid Crystals, 607:1, 23-31,
DOI: 10.1080/15421406.2014.927550
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Mol. Cryst. Liq. Cryst., Vol. 607: pp. 23–31, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.927550
Synthesis, Preparation, and Characterization
of Liquid Crystal/Organo-Montmorillonite
Nanocomposites
1
,2
1
SERAP MUTLU YANIC, DILEK GUZELLER,
1
1
1
HALE OCAK, FATIH CAKAR, ISMAIL EROL,
OZLEM CANKURTARAN, AND BELKIS BILGIN ERAN
1
,∗
1
1Yildiz Technical University, Department of Chemistry, Davutpasa Campus,
Istanbul, Turkey
2
Gedik University, Chemistry Technology Programme, Pendik,
Istanbul, Turkey
ꢀ
A new chiral calamitic liquid crystal 4 -((S)-3,7-dimethyloctyloxy)phenyl 4-(10-
undecen-1-yloxy)benzoate (DOPUB) has been synthesized and characterized by spec-
1
13
troscopic methods ( H-NMR and C-NMR). The focus is on the preparation of the
nanocomposites of new chiral calamitic liquid crystal DOPUB/Organo-montmorillonite
clay (OMMT) by solution intercalation method addition with OMMT contents 2.5, 5, and
7.5 wt% and determination of the morphology, thermal behavior, and crystalline prop-
erties of liquid crystal DOPUB/OMMT. Montmorillonite (MMT) modified by cationic
surfactant cetyltrimethylammonium bromide (CTAB) for increasing the interaction of
clay with DOPUB liquid crystal. The characterization of clay minerals and nanocom-
posites was investigated by X-ray diffraction. The mesomorphic behavior of liquid
crystal (DOPUB) and the nanocomposites was investigated by differential scanning
calorimetry (DSC) and optical polarizing microscopy (PM).
Keywords Liquid crystal; montmorillonite; nanocomposites
Introduction
In the recent years, polymer-inorganic nanocomposites have attracted a great deal of interest
due to their enhanced chemical, thermal, mechanical properties can be improved and new
high quality compounds [1–3]. In these nanocomposites, inorganic particles are dispersed at
a nanometer inside polymer matrix allows to obtain a product with improved performances
[4]. Nanocomposites materials exhibit hybrid properties derived from the polymer matrix
and inorganic particles. This hybrid technique should be able to be applied not only polymer
nanocomposites systems but also low molecular weight liquid crystals have a big potential
properties [5]. They have excellent properties leading to a various applications such as
opto-electronic devices, photonic crystal, depolarizers, scattering displays [6, 7].
∗
Address correspondence to Ozlem Cankurtaran, Department of Chemistry, Yildiz Technical
University, Davutpasa Campus 34220, Istanbul, Turkey. E-mail: kurtaran90@yahoo.com
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
23

24
S. M. Yanic et al.
The inorganic particles as a nanofillers generally used are clay minerals [8]. Among
the layered silicates, montmorillonite (MMT) is particularly effective as reinforcement
for the liquid crystal/clay hybrids systems because of their high surface area, low cost,
and especially high cation exchangeable capacity (CEC) [9]. In order to achieve good
dispersion of the MMT in the liquid crystal, the surface of MMT was modified by a suitable
approach in order to make them more organophilic and increase the interlayer distance
of the MMT, thus, liquid crystal are able to insert between the layers [4–10]. There are
+
+2
many exchangeable captions on the surface and interlayer of MMT such as Na , Mg ,
+
K . So cationic surfactants are generally used as modifiers such as alkyl ammonium salt
[
(
10]. The product consisted of modification of MMT was so-called organo-montmorillonite
OMMT).
In this study, firstly we synthesized and characterized a new chiral calamitic liquid crys-
ꢀ
tal 4 -((S)-3,7-dimethyloctyloxy)phenyl 4-(10-undecen-1-yloxy)benzoate (DOPUB) and
then we prepared the nanocomposites of DOPUB/OMMT by solution intercalation method
with loading OMMT content (2.5, 5, and 7.5 wt%). The effect of modification of the mont-
morillonite clay mineral with organic surfactant on the DOPUB/OMMT nanocomposites
was studied.
Experimental
Materials and Instrumentation
2
The montmorillonite clay was provided by Across Organics, surface area = 240 m /g. The
surfactant molecule is cetyltrimethylammonium bromide, of chemical formula C19H42NBr
(CTAB) was purchased by Merck. ((S)-3,7-dimethyloctyloxy chiral terminal group of
DOPUB liquid crystal was introduced from starting with commercial material (S)-(-)-
2
0
◦
β-Citronellol (Aldrich, ≥99.0%, [α] = −5.3 , neat).
D
X-ray diffraction (XRD) patterns were obtained using an Analytical Philips X’Pert-
Pro X-ray diffractometer with CuKα radiation of wavelength (λ = 0,154 nm) at the rate
◦
0
of 0.5 /min in the range of 5–80 (2θ) at room temperature. XRD analysis was carried out
on the clay mineral powder and on the dispersion of the montmorillonite in the DOPUB.
Mesomorphic properties were studied by optical microscopy using a Leica Polarizing
Microscope, equipped with a Metler FP-82 HT hot stage and control unit. Transition
thermal analysis was conducted by a differential scanning calorimetry (DSC) under nitrogen
atmosphere in a Perkin-Elmer calorimeter with a cooling system. About 8 (± 0.5) mg
◦
nanocomposites samples were crimped an aluminum pan and heated at a rate 10 C/min
from room temperature to −20 to 100 C in a nitrogen atmosphere.
◦
Synthesis, Characterization, and Liquid Crystalline Properties of DOPUB Liquid
Crystal
ꢀ
The synthesis of 4 -((S)-3,7-dimethyloctyloxy)phenyl 4-(10-undecen-1-yloxy)benzoate
(DOPUB) liquid crystal was carried out as shown in Scheme 1. (S)-(-)-β-Citronellol was
reduced to (S)-3,7-dimethyl-1-octanol under catalytic hydrogenation conditions (H2, Pd/C
in MeOH) [11] in the first reaction step of the DOPUB. Then, (S)-3,7-dimethyloctyl bro-
mide which was prepared from corresponding starting alcohol ((S)-3,7-dimethyloctanol)
as described by Jocelyn et al. [12] was used to introduce the chiral moiety at the
terminal position of DOPUB. The (S)-3,7-dimethyloctyloxy group was attached to 4-
benzyloxyphenol by etherification and then debenzylation [13] was realized under catalytic

Synthesis and Characterization of Liquid Crystal/Clay Nanocomposites
25
hydrogenation conditions to give 4-(S)-3,7-dimethyloctyloxyphenol. Finally, DOPUB
liquid crystal was obtained by the esterification of 4-(S)-3,7-dimethyloctyloxyphenol
with 4-(10-undecen-1-yloxy)benzoic acid [14] as procedures described previously
[15].
Scheme 1. Synthesis of the new chiral calamitic liquid crystal DOPUB
The characterization of the DOPUB is based on H-, 13C-NMR (Bruker Avance III
1
500 spectrometer in CDCl3 solutions, with tetramethylsilane as internal standard). The
proposed structure is in full agreement with the spectroscopic data.
ꢀ
The procedure for 4 -((S)-3,7-dimethyloctyloxy)phenyl 4-(10-undecen-1-
yloxy)benzoate (DOPUB): To a solution of the 4-(10-undecen-1-yloxy)benzoic acid
ꢀ
(
4.8 mmol) and 4 -(S)-3,7-dimethyloctyloxyphenol (5.2 mmol) in 40 mL of dry
dichloromethane, 5.9 mmol of dicyclohexylcarbodiimide (DCC) and 0.5 mmol of
dimethylaminopyridine (DMAP) as catalyst were added and the reaction mixture was
stirred at room temperature under an argon atmosphere for 24 h. The precipitate was
filtered off on silica gel and washed with dichloromethane (DCM). The solvent was
evaporated. The crude products were purified by column chromatography on silica gel
using dichloromethane as eluent and recrystallized from ethanol. Yield: 0.99 g (40%) of
1
white crystals. H-NMR (500 MHz, CDCl3) δ (ppm) = 8.13 (d, J ≈ 8.9 Hz; 2 Ar-H),
7
5
.09 (d, J ≈ 9.0 Hz; 2 Ar-H), 6.96 (d, J ≈ 8.9 Hz; 2 Ar-H), 6.92 (d, J ≈ 9.0 Hz; 2 Ar-H),
.86–5.77 (m; 1H, CH2 CH), 5.02–4.92 (m; 2H, CH2 CH), 4.04 (t; J ≈ 6.6 Hz; 2H,
OCH2), 4.01–3.95 (m, 2H, OCH2), 2.07–2.02 (m; 2H, CH2 CH-CH2), 1.86–1.78 (m; 3H,
CH2, CH), 1.69–1.43, 1.39–1.14 (2m; 21H, 1 CH, 10 CH2), 0.95 (d; J ≈ 6.6 Hz; 3H, CH3),
1
3
0
1
.87 (d; J ≈ 6.5 Hz; 6H, 2 CH3). C-NMR (125 MHz, CDCl3) δ (ppm) = 165.38 (CO),
63.44, 156.77, 144.35, 121.67 (Ar-C), 132.22, 122.48, 115.07, 114.24 (Ar-CH), 139.23
(CH2 CH), 114.16 (CH2 CH), 68.30, 66.73 (OCH2), 37.29, 36.23 (CH), 39.25, 33.82,
2
1
9.84, 29.50, 29.42, 29.35, 29.12, 29.11, 28.93, 27.99, 25.99, 24.68 (CH2), 22.74, 22.63,
9.66 (CH3).

26
S. M. Yanic et al.
Sample Preparation
Modification of Montmorillonite
The organic clay was prepared by exchanging the inorganic cation reaction of montmoril-
lonite with quaternary cetyltrimethylammonium bromide (CTAB). Montmorillonite clay
was dispersed in dimethyl sulfoxide (DMSO) by stirring. Cetyltrimethylammonium bro-
◦
mide was added to the dispersion. The dispersion was stirring for 24 hr at 80 C. After
modified clay was recovered by centrifugation, washed repeatedly with deinoized water
until supernatant solution was free of bromide ions was detected by addition of AgNO3,
◦
and finally dried at 60 C. The organoclay with CTAB is symbolized here after by OMMT
[16].
Preparation and Characterization of Liquid Crystal/Organo-Montmorillonite
Nanocomposites
The Liquid Crystal/Organo-Montmorillonite nanocomposites were prepared by solution
intercalation method using modified montmorillonite and new mesogen DOPUB. The
DOPUB/OMMT nanocomposites were obtained by compounding the modified clay mineral
OMMT with adding 2.5, 5, and 7.5 wt%. The organoclay was dispersed with chloroform
by constant magnetic stirring for 24 hr. DOPUB was dissolved in chloroform at room
temperature. Afterwards, two solutions were mixed and the dispersion was maintained by
◦
constant magnetic stirring at room temperature for 24 hr. The sample was dried at 25 C
under vacuum for a week [17–18].
Results and Discussion
Liquid Crystalline Properties
The mesomorphic properties of the obtained new chiral calamitic liquid crystal DOPUB
were investigated by optical polarizing microscopy and differential scanning calorimetry
(DSC). The transition temperatures, corresponding enthalpy values and mesophase type
observed for DOPUB are given in Fig. 1.
Figure 1. The chemical structure and phase transition temperatures of the DOPUB. (a) Perkin–Elmer
◦
DSC-6; heating (top lines)/cooling (bottom lines) rates were 10 C/min; enthalpy values are given in
square parentheses. Abbreviations: Cr = crystalline, Sm = smectic, Iso = isotropic liquid phase; (b)
Transition was detected by polarizing microscopy.

Synthesis and Characterization of Liquid Crystal/Clay Nanocomposites
27
Figure 2. The textures obtained between crossed polarizers as observed for the smectic phases of
◦
DOPUB (a) SmA phase on heating; (b) fan-shaped texture of the SmA phase at 46.0 C on cooling;
◦
◦
(
c) texture of the SmX phase at 33.0 C on cooling; (d) the SmX phase at 30 C on cooling.
The chiral calamitic liquid crystal compound DOPUB exhibits smectic mesophases at
low temperatures. On heating, the typical fan-like texture of the smectic A mesophase of
compound DOPUB is appeared as shown in Fig. 2. Although this phase transition is not
associated with a calculable peak in the DSC thermogram, a small detectable hump is ob-
◦
served at around 58 C in the heating curve (see Fig. 5). On cooling from the isotropic liquid,
SmA mesophase first develops a fan-shaped texture in planar alignment and homeotrop-
◦
ically aligned regions appearing completely dark. With decreasing temperature, at 35 C,
the fan-shaped texture of the mesophase does not change but some lines on fans starts
appearing, which becomes sharper as the temperature is reduced further. This mesophase is
assigned as SmX phase. No peak is observed for this transition in the DSC cooling curve.
On further cooling, optically there is no change, only a strong increase of the viscosity is ob-
served at lower temperatures. The typical textures of the smectic mesophases of compound
DOPUB are shown in Fig. 2.
Organo-montmorillonite and Nanocomposites Properties
The X-ray diffraction patterns at room temperature of purified MMT, modified OMMT and
◦
adding 2.5, 5, and 7.5 wt% DOPUB/OMMT nanocomposites in the region 2θ = 5–50
was investigated. The pattern of purified MMT exhibits a strong diffraction peak with the
mean interlayer spacing of the (001) plane, d001, given in Fig. 3. A typical diffraction
◦
peak of purified MMT is 2θ = 8.921 , responding to a basal spacing (d-spacing) of 9.90
Å. Montmorillonite is a smectite group with layered structure composed of silicate layers.

28
S. M. Yanic et al.
Figure 3. XRD of patterns of MMT (a) and OMMT (b).
+2
+2
+
These silicate layers are filled exchangeable cations such as Mg , Ca , Na , and water
molecules. In this study, the exchangeable cations of montmorillonite exchanged with
cetyltrimethylammonium bromide (CTAB). The pattern of modified OMMT was a peak
◦
at 2θ = 8.17 , responding to a basal spacing of 10.81 Å, given in Fig. 3. OMMT the
d001 reflection broadened and shifted to lower angles, that is larger d-spacing, compared
to unmodified MMT, indicating the exchange of inorganic cations in between the MMT
layers with organic cations. As a result of modification of MMT with CTAB, OMMT of
interlayered silicate layers expanded. The X-ray diffraction pattern of DOPUB/OMMT
nanocomposites showed that Fig. 4.
It was observed that there were XRD characteristic peaks for DOPUB liquid crystal
◦
in the range of 2θ = 14–26 . It was found that the diffraction peak positions are only
◦
slightly changed. The pattern of DOPUB exhibit a diffraction peaks are 2θ = 17.98 and
◦
2
3.36 , responding to a basal spacing of 4.93 Å and 3.80 Å, respectively. The patterns
of DOPUB/OMMT nanocomposites exhibit a diffraction peak are observed with DOPUB
Figure 4. XRD of patterns of OMMT (a), DOPUB (b), DOPUB/OMMT nanocomposites in the ratio
2.5 wt% (c), 5 wt% (d), and 7.5 wt% (e).

Synthesis and Characterization of Liquid Crystal/Clay Nanocomposites
29
Figure 5. DSC scans of compound DOPUB (a), DOPUB/OMMT nanocomposites in the ratio 2.5%
◦
(
b) 5% (c), and 7.5% (d) during the heating process (heating rates 10 C/min).
liquid crystal in the same characteristics peaks. However, the presence of the character-
istic reflection of modified clay in the liquid crystal indicates that layered silicate is not
observed within all the DOPUB/OMMT nanocomposites. The OMMT peak is dispersed
within the DOPUB/OMMT nanocomposites, indicating that intercalation of the new chiral
liquid crystal DOPUB within the modified clay OMMT occurs. As a result, exfoliated
DOPUB/OMMT nanocomposites (2.5, 5, and 7.5 wt%) could be prepared.
The thermotropic behavior of DOPUB/OMMT nanocomposites were also investigated
by POM and DSC. As seen from DSC, the heating and cooling curves in Figs. 5 and 6 of
DOPUB, OMMT modified clay and DOPUB/OMMT nanocomposites in the ratio 2.5 wt%,
5
wt%, 7.5 wt%, DOPUB/OMMT nanocomposites show only a monotropic smectic A phase
at lower temperatures, as indicated by small exotherms in the DSC cooling curves. Whereas
◦
an additional mesophase (SmX) occurs in the phase sequence of DOPUB at 35 C on
cooling, any textural transformations are not observed (compare textures in Fig. 7) before
Figure 6. DSC scans of compound DOPUB (a), DOPUB/OMMT nanocomposites in the ratio 2.5%
◦
(
b) 5% (c), and 7.5% (d) during the cooling process (cooling rates 10 C/min).

30
S. M. Yanic et al.
Figure 7. The textures obtained between crossed polarizers as observed for the smectic phase at (1)
◦
◦
3
6 C and (2) 25 C of DOPUB/OMMT nanocomposites in the ratio 2.5% (a) 5% (b), and 7.5% (c),
respectively.
crystallization point for DOPUB/OMMT nanocomposites. Comparing the mesomorphic
properties of the DOPUB liquid crystal with the DOPUB/OMMT nanocomposites shows
that mesophase type remains the same and mesophase transition temperatures decrease by
adding OMMT in the different ratio.
As compared with 2.5 wt% DOPUB/OMMT nanocomposite, the clearing points and
mesophase ranges of the DOPUB/OMMT nanocomposites in the ratio 5 wt% and 7.5 wt%
increase with increasing ratio of the modified clay mineral OMMT leading to a stabi-
lization of smectic mesophase. The SmA mesophase range of the nanocomposites 5 wt%
and 7.5 wt% are slightly broader than 2.5 wt% DOPUB/OMMT nanocomposite (see
Fig. 6). In addition, in the case of DOPUB/OMMT nanocomposites the transition from the
isotropic liquid to the SmA phase is broadened due to the fact that an additional mesophase
◦
(
SmX) occurs in the phase sequence of DOPUB liquid crystal at 35 C that is not observed
for DOPUB/OMMT nanocomposites. Hence, the only mesophase of DOPUB/OMMT
◦
nanocomposites, SmA, shows a mesophase interval which is about 16 C wider than that
observed for the DOPUB liquid crystal.
Conclusions
A new chiral calamitic liquid crystal DOPUB has been synthesized and investigated. The
DOPUB exhibits enantiotropic SmA and monotropic SmX mesophases at low tempera-
tures. The new chiral calamitic liquid crystal DOPUB/OMMT nanocomposites in the ratio

Synthesis and Characterization of Liquid Crystal/Clay Nanocomposites
31
2.5 wt%, 5 wt%, 7.5 wt% have been prepared in order to investigate the dispersion of the
liquid crystal in OMMT and compare the changes in the morphology, thermal behavior,
and liquid crystalline properties of DOPUB/OMMT nanocomposites. MMT modified by
CTAB for increasing the interaction of clay with DOPUB liquid crystal. By using the XRD
◦
analysis, we showed that the diffraction peak of purified MMT is 2θ = 8.921 , responding
to a basal spacing (d-spacing) of 9.90 Å. The pattern of organoclay OMMT was a peak
◦
at 2θ = 8.17 , responding to a basal spacing of 10.81 Å. By the modification of MMT
with CTAB, interlayered silicate layers of OMMT expanded. It was observed that there
were XRD characteristic peaks of modified clay in the liquid crystal DOPUB indicates that
layered silicate is not observed within all the DOPUB/OMMT nanocomposites. Compar-
ing the mesomorphic properties of the DOPUB liquid crystal with the DOPUB/OMMT
nanocomposites shows that the SmA mesophase only appears on cooling and the mesophase
transition temperatures decreased by adding OMMT in the different ratio 2.5 wt%, 5 wt%,
and 7.5 wt%. The SmA mesophase range of the nanocomposites in the ratio 5 wt% and
7.5 wt% are slightly broader than 2.5 wt% DOPUB/OMMT nanocomposite. It can be
concluded that in DOPUB/OMMT nanocomposites there is a considerable effect of the
insertion of OMMT in the different ratio on the mesophase stability compared to the pure
liquid crystal.
Acknowledgments
This research has been supported by the Yildiz Technical University Scientific Research
Projects Coordination Department (Project Number: 2012-01-02-KAP06).
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