Study on an electrorheological effect of side-chain polysiloxanes including fluorine atoms by the preshearing method

Article abstract of DOI:10.1080/15421400701613474

Side-chain liquid-crystalline polysiloxane derivatives possessing fluorinated mesogens that have positive dielectric-anisotropy parallel to the long axis of mesogen were synthesized to study phase-transition behavior and electrorheological (ER) effect of the polymers with a preshearing method. About 2000Pa increments in shear stress could be obtained after preshearing as an ER effect. In addition, shear rate dependence on shear stress as a function of temperature was investigated. As a result, it was shown that the preshearing treatment with high shear rate was important to generate a larger ER effect.

Full text of DOI:10.1080/15421400701613474

This article was downloaded by: [North Dakota State University]
On: 08 October 2014, At: 11:37
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Molecular Crystals and Liquid
Crystals
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gmcl20
Study on an Electrorheological
Effect of Side-Chain
Polysiloxanes Including
Fluorine Atoms by the
Preshearing Method
Kosuke Kaneko a , Yusuke Miwa a & Naotake
Nakamura a
a Department of Applied Chemistry , College of
Science and Engineering, Ritsumeikan University ,
Shiga, Japan
Published online: 22 Sep 2010.
To cite this article: Kosuke Kaneko , Yusuke Miwa & Naotake Nakamura (2007) Study
on an Electrorheological Effect of Side-Chain Polysiloxanes Including Fluorine Atoms
by the Preshearing Method, Molecular Crystals and Liquid Crystals, 473:1, 43-55, DOI:
10.1080/15421400701613474
To link to this article: http://dx.doi.org/10.1080/15421400701613474
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with

primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Mol. Cryst. Liq. Cryst., Vol. 473, pp. 43–55, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701613474
Study on an Electrorheological Effect of Side-Chain
Polysiloxanes Including Fluorine Atoms by the
Preshearing Method
Kosuke Kaneko
Yusuke Miwa
Naotake Nakamura
Department of Applied Chemistry, College of Science and Engineering,
Ritsumeikan University, Shiga, Japan
Side-chain liquid-crystalline polysiloxane derivatives possessing fluorinated
mesogens that have positive dielectric-anisotropy parallel to the long axis of meso-
gen were synthesized to study phase-transition behavior and electrorheological
(ER) effect of the polymers with a preshearing method. About 2000 Pa increments
in shear stress could be obtained after preshearing as an ER effect. In addition,
shear rate dependence on shear stress as a function of temperature was investi-
gated. As a result, it was shown that the preshearing treatment with high shear
rate was important to generate a larger ER effect.
Keywords: electrorheological (ER) effect; polysiloxane; preshearing
INTRODUCTION
Electrorheological (ER) fluids are materials whose rheological proper-
ties can be controlled by an external electric field. This phenomenon
is called the electrorheological (ER) effect. When the viscosity of an
ER fluid increases with applied electric field, this is termed the positive
ER effect. On the other hand, if the viscosity decreases with applied
electric field, this is called the negative ER effect. Some liquid-crystal-
line materials show a positive ER effect. In particular, a large ER effect
has been observed in side-chain liquid-crystalline polymers [1–3].
The effect of the liquid-crystalline materials arises from a change of
an orientation of the dielectrically anisotropic mesogens under the
Address correspondence to Kosuke Kaneko, Department of Applied Chemistry,
College of Science and Engineering, Ritsumeikan University, 1-1-1 Nojihigashi,
Kusatsu, Shiga 525-8577, Japan. E-mail: rc003987@se.ritsumei.ac.jp
43

44
K. Kaneko et al.
applied field. This effect is more remarkable when the materials have
a large positive dielectric anisotropy (De), i.e., De ¼ e ꢀ e > 0, where
?
k
e and e are values of the dielectric constant measured parallel and
?
k
perpendicular to the long axis of mesogen, respectively [4]. Therefore,
to obtain a larger ER effect, it is necessary to introduce a mesogenic
group where dielectric anisotropy is positive and large. For example,
the mesogens including halogen atoms in a terminal part parallel to
the long axis have a positive and large De [5].
A main disadvantage of the ER effect of the liquid-crystalline
polymers is high inherent viscosity, which disturbs the orientation of
the mesogens under an electric field. Recently, we proposed a new
method for the measurement of the ER effect of liquid-crystalline poly-
mers to cause a large increment of shear stress under the electric field.
This new method was named preshearing [6]. To arrange the terminal
mesogens to a shearing direction, a shear strain with high shear rate
(350 sꢀ1) was applied to the material before conventional measure-
ments of the ER effect. This caused a reduction in the inherent
viscosity when compared to that without preshearing.
In this research, side-chain liquid-crystalline polysiloxane deriva-
tives possessing fluorinated mesogens were synthesized, and phase-
transition behavior and the ER effect of the polymers with preshearing
were studied. Moreover, we investigated shear rate dependence on the
shear stress as a function of temperature.
EXPERIMENTAL
Synthesis
The synthetic procedure used in this research has been described in
our previous paper [6] and others [7]. Therefore, only the procedure
for new mesogens is described in detail here. Polysiloxane derivatives
were prepared by a typical hydrosilylation of allyl-bearing substituted
compound with 50–55% methylhydrosiloxane–dimethylsiloxane copo-
lymer containing Si-H groups under a platinum catalyst. Figure 1
shows a synthetic route of the polysiloxane derivatives. As is shown
later, the mesogens and the polysiloxane derivatives obtained here
are denoted by MF-n and PF-n (n ¼ 1,2,3), respectively, where n repre-
sents a number of fluorine atoms introduced in the mesogen.
4-Fluorophenyl-40-allyloxybenzoate (MF-1)
4-Allyloxybenzoic acid (4.45 g; 0.025 mol), 4-fluorophenol (2.80 g;
0.025 mol), and an excess amount of polyphosphate ester (PPE) (17 g)

Electrorheological Effect of Side-Chain Polysiloxanes
45
FIGURE 1 Synthetic route of the polysiloxane derivatives.
were dissolved in 150 ml of ether under an argon atmosphere, and the
mixture was refluxed for 24h. Then, 200 ml of water were added, and
the mixture was extracted with CH2Cl2. After the solvent was distilled
off, the residue was purified by column chromatography on silica gel
with CH2Cl2 as eluent. As a result, 2.30 g of 4-fluorophenyl-40-allylox-
ybenzoate were obtained as a white solid. Yield 35%. 1H NMR (CDCl3)
d: 8.14 (dt, 2H, J ¼ 9.4, 2.4Hz), 7.19–7.07 (m, 4H), 7.00 (dt, 2H,
J ¼ 9.6, 2.2Hz), 6.12–6.02 (m, 1H), 5.45 (dd, 1H, J ¼ 17.6, 1.5 Hz),
5.34 (dd, 1H, J ¼ 10.2, 1.5 Hz), 4.63 (d, 2H, J ¼ 5.4Hz).
3,4-Difluorophenyl-4’-allyloxybenzoate (MF-2) and 3,4,5-
Trifluorophenyl-4’-allyloxybenzoate (MF-3)
3,4-Difluorophenyl-40-allyloxybenzoate (MF-2) and 3,4,5-Trifluorophe-
nyl-40-Allyloxybenzoate (MF-3) were synthesized using 3,4-difluoro-
phenol and 3,4,5-trifluorophenol instead of 4-fluorophenol in the
1
same manner as mentioned previously. Data of H NMR of MF-2
and MF-3 are shown next.

46
K. Kaneko et al.
MF-2
1H NMR (CDCl3) d: 8.12 (dt, 2H, J ¼ 9.6, 2.2Hz), 7.21 (q, 1H,
J ¼ 9.3Hz), 7.12–7.07 (m, 1H), 7.02–6.93 (m, 3H), 6.07 (dq, 1H,
J ¼ 22.4, 5.4Hz), 5.45 (dd, 1H, J ¼ 17.1, 1.5Hz), 5.35 (dd, 1H, J ¼ 10.5,
1.2Hz), 4.64 (d, 2H, J ¼ 5.4Hz).
MF-3
1H NMR (CDCl3) d: 8.10 (dt, 2H, J ¼ 9.4, 2.2Hz), 7.00 (dt, 2H, J ¼ 9.4,
2.2Hz), 6.92 (dq, 2H, J ¼ 16.7, 4.6Hz), 6.09–6.05 (m, 1H), 5.45 (dd, 1H,
J ¼ 17.6, 1.5Hz), 5.35 (dd, 1H, J ¼ 10.5, 1.2Hz), 4.64 (d, 2H, J ¼ 5.4Hz).
Characterization
1H NMR measurements were made by a Jeol Alpha-400 FT NMR
(400 MHz) spectrometer using CDCl3 and DMSO as a solvent.
Gel-permeation chromatography (GPC) measurements were carried
out by a Tosoh HLC-8020 instrument with tetrahydrofuran as eluent
to check the purity of the polymers. Standard polystyrenes were used
for calibration.
Transition temperatures of the materials were determined by
differential scanning calorimetry (DSC) using a Mettler DSC30
calorimeter at scanning rate of 4, 9, 16, 25ꢁC=min. The transition tem-
peratures were identified by extrapolation with on-set temperatures
obtained at each scanning rate. Textures of the liquid-crystalline
phase were observed using an Olympus BX51 polarizing optical micro-
scope (POM) equipped with a Linkam THMS 600 hot stage and TMS
94 thermocontrol system.
X-ray difraction measurement was carried out using Laue camera.
The Cu Ka radiation was used from a Rigaku generator operating at
30 kV and 15mA, and an Ni filter was utilized in front of the detector
(k ¼ 0.154 nm). The distance between sample and imaging plate was
45 mm, and the measurements were performed at 20ꢁC under vaccum
to prevent a scattering of the air.
Measurements
The rheological properties were measured by a rotational rheometer
(Rheosol-G2000, UBM Ltd.) equipped with an electric field controller
(Matsusada Precision Devices high-voltage supply). All measurements
were performed using parallel plates with a diameter of 25mm and a
gap of 0.1mm. Because the fixtures did not provide a uniform shear
strain, shear rates reported in this article have been defined as the
shear rate at the edge of the plate.

Electrorheological Effect of Side-Chain Polysiloxanes
47
The measurements were carried out as follows. The sample was
placed between the parallel plates in the isotropic phase and was held
at the temperature in the isotropic phase for about 10 min. Then, the
sample was cooled to the desired temperature, and the gap was read-
justed to 0.1mm long. Generated shear stress was defined as the
difference between the measured shear stresses with and without
applied electric field. Then, the sample was sheared with high shear
rate (300–400 sꢀ1) for about 5min before the measurement in gain a
lower viscosity. After the preshearing, rheological properties under
an electric field were measured at each temperature. The electric field
of 2 kV=mm was applied between upper plate and lower one with
shearing at a constant shear rate (50sꢀ1), when the ER effect was
measured.
With regard to the measurement of shear stress as a function of
shear rate, shear stress was measured with increasing shear rate at
each temperature. Note that shear rate was increased step by step
from 0sꢀ1 to 500 sꢀ1
.
RESULTS AND DISCUSSION
Phase-Transition Behavior
DSC curves of the polymers synthesized here are shown in Fig. 2, and
phase-transition temperatures are summarized in Table 1, in which
the temperatures are determined by an extrapolation against 0 scan-
ning rate using on-set temperature of the peaks obtained by various
scanning rates of DSC measurements. For PF-2 in Fig. 2b, a sharp
exothermic peak was observed at around 28ꢁC. This peak was ident-
ified as a transition point from an isotropic liquid to a liquid-crystal-
line phase, because a sand texture was observed by polarizing
optical microscope just below the peak. This sand texture changed into
ˆ
a batonnet one by annealing. These results suggested that this phase
has a possibility of being smectic A. These textures are shown in
Figs. 3 and 4, respectively. In addition, the typical smectic A diffrac-
tion pattern was obtained by X-ray diffraction. The diffraction pattern
is shown in Fig. 5. Sharp spots are observed in the horizontal direc-
tion, and broad peaks exist in vertical ones, respectively. Under this
clearing point, the side chains containing mesogenic groups were
arranged in a director. Thermal molecular motion of backbones was
slowing down from the clearing point with decreasing temperature,
and finally it became difficult at around ꢀ17ꢁC, accompanying
shoulder of the peak in the DSC curve. Under the temperature, the
motion of the side chains was still possible, but the motion began

48
K. Kaneko et al.
FIGURE 2 DSC curves of (a) PF-1, (b) PF-2, and (c) PF-3 on the cooling process.
slowing gradually with decreasing temperature, and subsequently it
stopped. The motion was frozen at around ꢀ48ꢁC. Therefore, it was
identified as the glass transition point.
On the other hand, PF-1 had a broad peak corresponding to its
clearing temperature. The broadening of the peak is attributed to an
existence of a shoulder very close to the peak. The clearing point
was observed at 18.0ꢁC, and no glass transition point was observed
TABLE 1 Phase-Transition Behavior Observed by DSC
on Cooling Process
Sample
Tg (ꢁC)
Tcl (ꢁC)
PF-1
PF-2
PF-3
G
G
G
—
ꢀ48.0
—
SmA
SmA
SmA
18.0
27.8
15.6
IL
IL
IL
Note. G: glass state; SmA: smetic A; IL: isotropic liquid. The
transition temperatures were determined with on-set value.

Electrorheological Effect of Side-Chain Polysiloxanes
49
ꢁ
FIGURE 3Sand texture of PF-2 takenC. at 25
in the temperature range of the DSC measurements. Phase-transition
behavior of PF-3 was fairly similar to that of PF-1. Molecular motions
of the siloxane backbone and side chains are considered to exhibit
basically similar behavior.
The characteristic point of PF-1 and PF-3 is that these two com-
pounds showed a broader peak at around the clearing point compared
with that of PF-2. In general, the shape of the phase-transition peak of
liquid-crystalline polymers could be influenced by molecular-weight
distribution. Values of molecular-weight distribution determined by
GPC were 1.34 for PF-1, 1.33 for PF-2, and 1.35 for PF-3, respectively.
ˆ
FIGURE 4 Batonnet texture of PF-2 after annealing.

50
K. Kaneko et al.
ꢁ
FIGURE 5X-ray diffraction pattern for PF-2C. at 20
This suggests that the influence of the molecular-weight distribution
on the broadness of the peaks of PF-1 and PF-3 was ruled out because
these three values are regarded as almost the same.
ER Effect
Figures 6a and b shows the ER effect results of PF-1 without and with
pre-shearing, respectively. These measurements were performed with
50 sꢀ1 of shear rate. In both cases, shear stress apparently increased
with lowering temperature. As shown in Fig. 6a, the ER effect was
not observed at all at each temperature. Figure 6b showed that shear
stresses with the preshearing became lower than those obtained with-
out preshearing, especially at a lower temperature range. Then, ER
effect could be observed at low temperature, though an increment of
shear stress was not observed in the higher temperature range.
Shear stress at 50ꢁC and 60ꢁC in Figs. 6a and b could not be
increased by the applied electric field. This was not due to the high
inherent viscosity of the sample. This was attributed to a relatively
active thermal motion of the polymer backbones and flexible spacers
under such temperature. It may be possible to arrange the terminal
mesogens parallel to the applied electric field in this state. However,
the orientation was unable to be detected well as flow resistance. In
other words, the sample itself may move to the shearing direction.
Consequently, the increment in shear stress became too small.

Electrorheological Effect of Side-Chain Polysiloxanes
51
FIGURE 6 Shear stress of PF-1 under an applied electric field (2 kV=mm)
with (a) no preshearing and (b) preshearing.
At temperatures colder than 40ꢁC, the ER effect was observed at each
temperature by means of preshearing.
Results of the ER effect of PF-2 and PF-3 are shown in Figs. 7 and 8,
respectively. Both compounds showed the ER effect after preshearing.
For PF-2, shear stress at about 30ꢁC could not be measured because of
an overloaded torque at low temperature. This was caused by the forma-
tion of the liquid-crystalline phase. It is assumed that microscopic mol-
ecular motion forming a liquid-crystalline phase began at around 30ꢁC.
PF-3 showed the largest increase in shear stress as the ER effect in
a wider temperature range. As shown in Fig. 8b, increase in shear
FIGURE 7 Shear stress of PF-2 under an applied electric field (2 kV=mm)
with (a) no preshearing and (b) preshearing.

52
K. Kaneko et al.
FIGURE 8 Shear stress of PF-3 under an applied electric field (2 kV=mm)
with (a) no preshearing and (b) preshearing.
stress by an applied electric field was estimated to be about 2000 Pa at
20ꢀC, 25ꢀC, and 30ꢀC. In the case of ER fluids composed of low-molecular-
weight liquid-crystalline materials, the increase in shear stress is
relatively smaller than that of liquid-crystalline polymers, though
the response time is fast. For example, the enhanced shear stress of
liquid-crystalline oligomers remained up to about 1000 Pa and was
reported as the ER effect [8]. A few thousand generated shear stress
is better taken into account for mechanical application. Therefore,
it is considered that the generated shear stress observed in this study
is large enough for commercial use.
A clearing point of PF-3 was observed at 15.6ꢀC, and the ER effect
was observed above the clearing point. Similar behavior was already
observed by Inoue et al. [6]. It is likely that molecular arrangement
begins gradually just above the clearing point when the measuring
temperature approaches the clearing point in the cooling process. This
state may be suitable for appearance of the ER effect because the poly-
mer probably possesses middle viscosity between an isotropic liquid
and liquid-crystalline phase. In addition, preshearing could be more
useful in the region just above the clearing point because of easy
arrangement of the mesogens to a shearing direction.
The fluorine atom is one of the strongest electronegative elements.
Introduction of plural fluorine atoms into terminal part of mesogen
results in a larger positive dielectric-anisotropy parallel to the long
axis of mesogen. Therefore, it is correct that PF-3 showed a larger
ER effect in the wider temperature range. It can be said that a large
positive dielectric anisotropy led to the larger ER effect and played

Electrorheological Effect of Side-Chain Polysiloxanes
53
an important role in giving rise to orientation of the mesogens under
an applied electric field.
Rheological Behavior
Shear rate dependence on shear stress of PF-3 is shown in Fig. 9.
Applied shear rate was from 0sꢀ1 to 500 sꢀ1. At 60ꢁC and 50ꢁC, shear
stress was in proportion to the shear rate, which is known as a beha-
vior of Newtonian fluid. At 40ꢁC, a similar behavior was also observed
until 200 sꢀ1, and then the shear stress deviated from the Newtonian
behavior. This may indicate that structural change in the sample will
occur, for example, separation of entanglement among polymer back-
bones, an orientation of terminal mesogens toward a shearing direc-
tion, and so on. This deviation from the Newtonian behavior was
also observed on 100 sꢀ1 at 30ꢁC and 50 sꢀ1 at 25ꢁC, respectively. At
20ꢁC, shear stress could not be measured at more than 70 sꢀ1 because
of its high viscosity, which was greater than the detection limit of the
instrument. It is clear that a deviation from the Newton behavior
occurred earlier upon decreasing the temperature. Results of shear
rate dependence on shear stress of PF-1 and PF-2 were almost similar
to that of PF-3.
By means of the data obtained here, it was found out that a shearing
with high shear rate apparently caused some changes in the samples,
such as an arrangement of terminal mesogens toward a shearing
FIGURE 9 Shear rate dependence on shear stress of PF-3.

54
K. Kaneko et al.
direction. In addition, a larger ER effect could be observed after
preshearing, as shown in the previous section. In Newtonian behavior
observed in the low-shear-rate range, response of shear stress was
proportional to shear rate, suggesting that the internal change of the
sample did not occur. Therefore, preshearing with high shear rate
evidently caused the terminal mesogens to arrange to a shearing direc-
tion. It can be strongly concluded that preshearing is one of the most
useful methods for the ER effect measurements in side-chain liquid-
crystalline polymers.
CONCLUSIONS
In this study, side-chain liquid-crystalline polysiloxanes with fluorine
atoms in mesogenic groups were synthesized and their rheological
properties were investigated. In the measurement of the ER effect,
PF-3 (of which the dielectric anisotropy in the mesogenic group was
largest within the samples studied here) showed the largest increment
of viscosity. A large positive dielectric anisotropy led to a larger
increment of the shear stress, and the orientation of the mesogens
under an applied electric field was one of the main factors showing
the ER effect.
We could show the importance of preshearing with high shear rate,
which generated a larger ER effect. In this case, we should apply pre-
shearing with a higher shear rate at which shear stress completely
deviated from Newtonian behavior.
ACKNOWLEDGMENT
We express our thanks to Tomonori Hanasaki (Ritsumeikan University,
Japan) for valuable and fruitful discussion and Tomoki Nakano and Eigo
Katsuura for the synthesis of the polymers and the measurement of the
´
ER effect. Philippe Martinoty and Daniel Rogez (Unite Mixte de
´
Recherche CNRS-ULP, Universite Louis Pasteur, France) are also
acknowledged for their partial support for differential scanning calori-
metry (DSC) measurement. A High-Tech Research Center Project for
Private Universities matching fund subsidy from Ministry of Education,
Culture, Sport, Science, and Technology is gratefully acknowledged for
partial support of this work (2006).
REFERENCES
[1] Inoue, A. & Maniwa, S. (1995). J. Appl. Polym. Sci., 55, 113.
[2] Inoue, A. & Maniwa, S. (1995). J. Appl. Polym. Sci., 59, 797.

Electrorheological Effect of Side-Chain Polysiloxanes
55
[3] Inoue, A., Maniwa, S., & Ide, Y. (1997). J. Appl. Polym. Sci., 64, 303.
[4] Ning, Y. & Alex, M. J. (1997). Macromolecules, 30, 5822.
[5] McDonnell, G. D., Raynes, P. E., & Smith, A. R. (1989). Liq. Cryst., 6, 515.
[6] Kaneko, K. & Nakamura, N. (2007). Liq. Cryst., 34, 229.
[7] Kanaoka, Y., Tanizawa, K., Sato, E., Tonemitsu, O., & Ban, Y. (1967). Chem. Pharm.
Bull., 15, 593.
[8] Nakamura, N. & Kojima, A. (2007). Mol. Cryst. Liq. Cryst., 465, 15.