PHYSICAL REVIEW E 86, 011710 (2012)

Rheological properties of a reentrant nematic liquid crystal
J. Ananthaiah,1 M. Rajeswari,1 V. S. S. Sastry,1 R. Dabrowski,2 and Surajit Dhara1,*
1
School of Physics, University of Hyderabad, Hyderabad 500046, India
Institute of Chemistry, Military University of Technology, 00-908 Warsaw, Poland(Received 20 February 2012; revised manuscript received 2 June 2012; published 25 July 2012)2

We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheologicalproperties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture
exhibits nematic (N ) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (NR ) phasetransition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases
observed from SALS experiments is attributed to the realignment of the director within the domains. The domains
are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity
and static dielectric constant reveals the changes in the director orientation across N -SmA-NR phase transitions.
At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at muchhigher fields. It also exhibits two anomalous peaks across N -SmA-NR phase transitions beyond a particular field.
The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both
low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased
dislocation density.
DOI: 10.1103/PhysRevE.86.011710

PACS number(s): 83.80.Xz, 83.10.Tv, 83.50.Ax

I. INTRODUCTION

Liquid crystals are orientationally ordered fluids made ofanisotropic organic molecules. They exhibit a variety of phasetransitions owing to their molecular structures and shapes.
Common mesophases exhibited by low molecular weightliquid crystals (LCs) are typically nematic (N), smectic-A(SmA) and cholesteric (N ∗ ). The flow properties of theseLCs are very interesting and there are many theoretical andexperimental studies on the flow viscosities [1–14]. Nematic
liquid crystals (NLCs) in this respect are relatively simpler andhave been investigated in detail [3]. The average alignment
direction of the long axes of the molecules is called the
director and is denoted by a dimensionless unit vector n.
When the sample is sheared the director exhibits mainly three
types of orientation with respect to the flow and the velocity
gradient directions. Schematic representations of the director
orientations in N as well as in SmA phases are shown in
Fig. 1. The orientation of the director depends on the relative
magnitude and sign of the two Leslie coefficients, α2 andare negative the director
α3 . If both of these coefficients√aligns at an angle θ = tan−1 ( α2 /α3 ) with respect to the flow
direction [4,15–17]. In this orientation the measured viscosityis η2 (Miesowicz viscosity). Safinya et al. [13] reported that thedirector orientation changes with temperature in compounds
exhibiting N-SmA phase transition. They showed theoreticallyand experimentally that α3 is renormalized (α3R > 0) due to thecritical slowing down of the SmA order-parameter fluctuationsin the N phase, and the ratio α2 /α3 is negative [13,14]. As aresult the director orientation changes from the flow direction
to a neutral direction (x axis) as shown in Fig. 1(a). Later it was
shown that in the case of freely flowing nematic liquid crystals
the measured viscosity changes from η2 to η3 at a few degrees
below the nematic-isotropic (NI) transition [18,19]. It suggeststhat just below the NI transition the director is oriented along*

Corresponding author: sdsp@uohyd.ernet.in

1539-3755/2012/86(1)/011710(6)the velocity direction (Fig. 1(b)) and changes its orientation to
the neutral direction (as shown in Fig. 1(a)) as the temperatureis reduced. Bhattacharya et al. measured flow viscosity in anoriented sample showing SmA-to-NR phase transition [20] andreported that the flow behavior of the NR phase is identical tothat of the higher temperature nematic phase.
Using synchrotron x-ray studies Safinya et al. [14] showedthat several steady state structures appear in compounds
exhibiting N -SmA transition due to the precessional motionof the director along the neutral direction [14] denoted by am ,as , a(b), and ac . These structures are described by the equation of an ellipse: n2y (t)/n2y0 + n2z (t)/n2z0 = 1, where ny (t) =ny0 cos(ω0 t) and nz (t) = nz0 sin(ω0 t) are components of thedirector n(t) = (nx (t),ny (t),nz (t)). The angular√ frequency ofthe precessional motion is given by ω0 = γ˙2 (−α2 α3R )/γ12 ,where α3R is the renormalized Leslie coefficient, γ̇ is the shear
rate, and γ1 = α3 − α2 [14]. These structures are physicallyinterpreted as follows. In am structure, the precessional motion
is anisotropic with larger amplitude in the y direction thanin the z direction (ny0 > nz0 ); in as structure, the isotropic
precession occurs with equal amplitudes in both directions(ny0 = nz0 ); in a(b) structure, anisotropic precession occurs
with lesser amplitude in the y direction than in the z direction(ny0 < nz0 ); and in ac structure, anisotropic precession occurs
with a very large amplitude in the z direction (ny0 $ nz0 ).
Negita et al. [21] reported that the above structural features
are also reflected in the rheodielectric measurements on
octyl cyanobiphenyl (8CB) compound which exhibits N-SmA
phase transition. Very recently we showed that the viscosity
increases and the director orientation changes under theapplication of an external electric field when the temperature is
reduced in octyloxy cyanobiphenyl (8OCB) [22]. The rheodielectric measurements mostly provide overall information on
the director orientation during the flow. However, small angle
light scattering (SALS) measurements have the potential toinfer the effect of domain shape and size on the rheologicalproperties and such studies are meager in these materials.
In addition, the flow behavior and hence the rheological

011710-1©2012 American Physical Society

PHYSICAL REVIEW E 86, 011710 (2012)

J. ANANTHAIAH et al.

FIG. 2. (Color online) Schematic representation of the parallel
plate setup for simultaneous measurement of rheological and dielectric properties.

FIG. 1. (Color online) Schematic representation of the threefundamental director orientations in the N and SmA phases undershear. The director orientations are along the x (neutral), y (velocity),and z (velocity gradient) directions, denoted a, b, and c, respectively.
%%
Similar director orientation in the SmA phase is denoted by a , b ,%and c . Layer orientations in the SmA phase are shown by dottedlines. Miesowicz viscosities corresponding to each orientation in the
N phase are designated by η3 , η2 , and η1 , respectively.

properties across the SmA-to-NR transition are very rare andinteresting from a phase transition point of view.
In this paper we report SALS, rheodielectric, and electrorheological studies on a binary mixture of hexyloxy
cyanobiphenyl (6OCB) and 8OCB and investigate the effectof an external ac electric field on the effective viscoelastic
properties. We emphasize that the flow behavior and effectof presmectic fluctuations are similar in both N and NR
phases. The viscoelasticity in the SmA phase is dominatedby dislocations and shows an interesting variation on theapplication of an external field.
II. EXPERIMENTThe compounds 8OCB and 6OCB were synthesized in ourlaboratory in Poland. 6OCB exhibits only the N phase, while
8OCB exhibits both N and SmA phases. A 6OCB with 8OCB
mixture of 21.0 to 29.5 wt% exhibits the reentrant nematic (NR )phase. There have been several studies on the phase transitionsin these mixtures [23,24]. We have chosen a mixture of 27
wt% of 6OCB and 73 wt% of 8OCB that exhibits a reasonably
wide temperature range (&10◦ C) of the SmA phase above
the reentrant nematic phase. The mixture shows the following
phase sequence as observed in a polarizing optical microscopeon cooling: NR 32.4◦ C; SmA 43.2◦ C; N 77.5◦ C I. Rheologicalmeasurements were performed using a rheometer (Anton Paar
MCR 501) in parallel plate geometry with a plate diameterof 50 mm. The parallel plate configuration was chosen forthe simultaneous measurement of rheological and dielectric
properties. The gap between the two parallel plates was 75 µm.

The schematic diagram for measuring the rheodielectric
properties is shown in Fig. 2. An electric field was applied
between the bottom and the top plates by using a low friction
spring wire (Fig. 2). The air correction (i.e., the contribution
due to the small friction in the absence of the sample) was
estimated. These values were subtracted from the measured
quantities in the presence of the sample at all temperaturesand electric fields. The temperature variation of the dielectric
constant was measured by measuring the ratio of the sample
capacitance with that of the capacitance of an empty cell(i.e., without sample). The temperature of the sample wascontrolled by a Peltier temperature controller with an accuracy
less than 0.1◦ C. The heater and the measuring system were
kept inside a protective cover for uniformity of the sample
temperature. The dielectric constant was measured as afunction of temperature up to 20 V with an inductancecapacitance-resistance (LCR) meter (Agilent E4980A). For
voltages beyond 20 V we used a signal generator (Tektronix
AFG3102) and a high voltage amplifier (TEGAM). The
frequency of the sinusoidal voltage was 3.11 kHz for all themeasurements. The experimental setup for SALS is shownin Fig. 3, and parallel glass plates of diameter 43 mm wereused in these measurements. The upper limit of temperatureof the SALS experiment is 70◦ C. A polarized diode laser ofwavelength 658 nm was directed to the sample. An analyzer
crossed with respect to the polarizer, a beam stopper, and afocusing lens were adjusted to obtain the scattering pattern on
the screen. A CCD camera was used to record the scattering
pattern. Samples were prepared by physical mixing without
any solvent and all the measurements were made upon coolingthe sample from the isotropic phase.
III. RESULTS AND DISCUSSION
A. SALS measurements

We first present the variation of effective shear viscosity(ηef ) in a quenched sample with shear rate, in both N and SmA
phases (Fig. 4). In the N phase ηef is very high (&700 mPa s) in
the low shear rate region (e.g., γ̇ = 0.1 s−1 ) and exhibits strong
shear thinning behavior. For example, it reduces to &35 mPa s
at γ̇ & 10 s−1 . Beyond this shear rate ηef is constant and hence
behaves like a Newtonian fluid. The shear rate dependent
effective viscosity in the N phase can be described using the011710-2

PHYSICAL REVIEW E 86, 011710 (2012)

RHEOLOGICAL PROPERTIES OF A REENTRANT NEMATIC . . .

where η∞ and n are the asymptotic value of the viscosity (atvery high shear rate) and the power-law index, respectively.
The best fit to the Sisco model is shown in Fig. 4. The index n
is about 0.8 and comparable to the previously reported value[26]. In the SmA phase ηef is about ten times higher than in
the N phase and exhibits shear thinning behavior up to γ̇ =50 s−1 . At higher shear rate ηef does not saturate, indicating
the presence of multiple shear thinning events.
The depolarized scattering patterns obtained from thehorizontal-vertical orientation of the polarizers (HV) at some

representative shear rates are also shown in Fig. 4, and theshape remains symmetric (almost circular) up to γ̇ = 10 s−1
in the N phase. Beyond this shear rate the shape is elongatednormal to the shear direction and tends to be elliptical.
Nematic liquid crystals normally exhibit a polydomain texture,
separated by spatially distributed disclination lines. Since
SALS measures the image in the q space, it suggests that,
below γ̇ = 10 s−1 , the reorientation of the director takes
place such that it tends to orient parallel to the shear plane
without affecting the domain shape. At higher shear rate thepolydomain texture is elongated along the shear direction. In
the SmA phase a non-Newtonian flow behavior is observed in
the entire range of shear rate, and beyond γ̇ = 50 s−1 the onsetof elongation of the scattering pattern is observed. Thus, thisthreshold shear rate is almost five times larger than that of the Nphase. The SmA phase has focal conic domains with spatiallydistributed dislocations in the sample. The realignment of
the director, and hence the SmA layers, take place withinγ̇ = 50 s−1 . The elongation of domains occurs beyond thisshear rate. This was also observed previously in a polarizing
optical microscope [27] but the shear rate dependent shape was
not reported. It may be mentioned that the scattering intensity
also increases with shear rate in both phases and similar
behavior was also observed in other systems [28,29]. Since
HV scattering in the present sample arises preliminarily fromorientational fluctuations, it suggests that these fluctuations are
increasing with shear rate.
We measured the temperature dependent effective viscosity(ηef ) at a steady shear rate (γ̇ = 50 s−1 ) and recorded thescattering patterns at some representative temperatures toinvestigate the domain structure. It was not possible to record
SALS patterns above T − TNI & −15◦ C due to the limitationsof the associated temperature controller. In Fig. 5 we present
the variation of ηef with temperature and a few SALS patterns.
We find that ηef decreases in the N phase just below theNI transition. This is due to the shear-induced alignment of
the director along the shear direction as shown in Fig. 1(b).
Below T − TNI = −4◦ C, ηef begins to increase, suggesting the

FIG. 4. (Color online) Shear rate dependent effective shear
viscosity (ηef ) in N (T − TNI = −30◦ C) and SmA phases (T −TNI = −43◦ C). The depolarized scattering patterns (HV) at some
representative shear rates are shown in both the phases. The redarrow indicates the direction of shear. The upper and lower scattering
patterns correspond to the SmA and N phases, respectively. The
continuous line is a best fit to Eq. (1).

FIG. 5. (Color online) Temperature variation of effective shear
viscosity (ηef ) at a steady shear rate (γ̇ = 50 s−1 ). HV scattering
patterns at a few temperatures. The red arrow indicates the directionof shear. The possible director orientations at different temperatures
are also indicated considering the similarity of temperature dependentzero-field viscosity of 8CB [21] and 8OCB [22].

FIG. 3. (Color online) Schematic representation of small angle
light scattering (SALS) setup with the rheometer.

Sisco model [25]
η = η∞ + a γ̇ −n ,(1)011710-3

PHYSICAL REVIEW E 86, 011710 (2012)

J. ANANTHAIAH et al.

onset of a mixed director orientation (i.e., a-b structure). The
viscosity increases almost linearly up to T − TNI & −25◦ C.
A small slope change below this temperature, followed bya rapid increase of the viscosity in the SmA phase, isobserved. Similar behavior of ηef was also observed above
the N -SmA phase transition in pure 8CB and 8OCB liquid
crystals [21,22]. It was explained based on the occurrenceof various structures, namely ac , a(b), as , and am , that arise
because of precessional motion of the director, discussed
earlier. The scattering patterns at this shear rate (γ̇ = 50 s−1 ) in
the N phase (Fig. 5) are elongated perpendicular to the shear
direction due to the deformation of domains, as explained
previously. The orientation of the patterns at N-SmA andSmA-NR transitions is noticeably different in the sense thatthe long axis of the ellipse is rotated by an angle &45◦ to theleft side of the shear direction. This implies that the elongation
directions of the domains are rotated by the same angle on theright side of the shear direction. It seems that the precessionalmotion of the director (as described by Safinya et al. [14]) also
induces significant change in the microtexture of the sample. In%%
the SmA phase the domains have c and a director orientation(Fig. 1), and the scattering pattern is almost circular (Fig. 5),
suggesting that the shapes of the domains remain unaffected
at this shear rate. This is also consistent with the observationin Fig. 4. In the NR phase the viscosity decreases sharply andagain the scattering pattern gets elongated perpendicular to theshear direction.
B. Rheodielectric and electrorheological measurements

To investigate the director orientation inside the domain wemeasured the effective dielectric constant (&ef ) simultaneouslywith the viscosity measurement as a function of temperature
at various fields. First we show the electric field-dependent
effective viscosity (ηef ) as a function of temperature in
Fig. 6(a). Its behavior at a low field (i.e., 0.8 × 104 V/m)
was already discussed in Fig. 5 and is presented here again forthe purpose of comparison with the data at higher field. At a
fixed temperature in the N phase, ηef increases with electricfield and saturates beyond a threshold value (26.7 × 104 V/m).
It exhibits two anomalous peaks [Fig. 6(a)] across N -SmA-NR
phase transitions beyond a particular field (>13.3 × 104 V/m).
At much higher field the peaks become sharper and they tend
to get suppressed beyond &93.3 × 104 V/m [Fig. 6(a), inset].
The anomalous behavior of ηef across the N -SmA transition
was also observed in a few liquid crystals and it was attributed
to the significant contribution of the Leslie coefficient α1 near
the N -SmA transition [10,30]. Since the hydrodynamic theoryof both the N and NR phases is expected to be the same [20],the second peak across the SmA-NR transition could be dueto the similar effect. Furthermore, it may be noted that boththe peaks are asymmetric in shape with temperature and thesecond peak is relatively stronger than the first one. The originof this asymmetry in not clear, however; the difference in thesmectic short-range order in both N and NR phases could be
responsible.
The variation of &ef that was measured simultaneously withthe viscosity measurement is shown in Fig. 6(b). At zero shear
rate and low field (0.8 × 104 V/m) in the N phase, &ef islower than in the I phase, suggesting that the parallel plate

FIG. 6. (Color online) (a) Variation of effective shear viscosity(ηef ) with temperature at various ac electric fields. All the data werecollected at a steady shear rate (γ̇ = 50 s−1 ). Inset: Suppression ofpeaks under strong electric fields. (b) Static dielectric constant atsame shear rates and same electric fields as in (a). The dielectric
data represented by star were measured without shear and at a field
0.8 × 104 V/m. The frequency of the applied field is 3.11 kHz.

induces planar orientation of the director. Since the dielectricanisotropy ('& = &|| − &⊥ ) of the mixture is positive [31]we essentially measure the perpendicular component, i.e.,&ef & &⊥ . In the SmA phase &ef is comparatively lower thanboth the N and the NR phases, indicating a strong antiparallelcorrelation of the transverse component of the dipole momentsin the SmA layers [32]. At the same field the temperature
variation of &ef is significantly different when the sample
is subjected to a steady shear rate (γ̇ = 50 s−1 ), especiallybelow T − TNI = −10◦ C. This is because of the orientationalchange of the director across the phase transitions. In the SmA
phase &ef is slightly larger than the values in both N and NR%%
phases due to the a -c orientation of SmA layers as describedin Fig. 5. At an intermediate field (e.g., 13.3 × 104 V/m),&ef just below the NI transition is much larger than in the Iphase and decreases gradually with decreasing temperature.
Initially the director tends to orient along the field direction
as '& > 0. On the other hand, due to the effect of shear andpresmectic fluctuations it tends to be parallel to the shear planewith decreasing temperature. Thus, at every temperature thedirection of director orientation is determined by these twocompeting force fields. When the electric field is increased

011710-4

PHYSICAL REVIEW E 86, 011710 (2012)

RHEOLOGICAL PROPERTIES OF A REENTRANT NEMATIC . . .

to 26.7 × 104 V/m, &ef is much higher and &ef & &|| [33] anddecreases gradually as the N -SmA transition is approached.
In the SmA phase &ef again increases and reaches a maximum
value (&ef & 15) which is slightly less than that measured in
the N phase (near the NI transition), suggesting that the layer%
orientation in this phase is almost c type.
C. Field-dependent complex shear modulus measurements

The experimental results from the SALS measurement
provided qualitative information about the microtexture, andthe rheodielectric properties revealed the changes in the
director orientation. In the phase diagram of this binary mixture
the SmA phase is surrounded by the nematic phase [23] and has
different types of defects (dislocations). We anticipated that theinvestigation on the shear modulus across the phase transitions
could be interesting in the sense that the applied electric field
can change the defect density. Hence we measured the storage%%%and loss moduli (G and G ) as a function of temperature. In%%%
Fig. 7 we show the variation of G and G as a function oftemperature at various applied electric fields. At a low field%%%(0.8 × 104 V/m) G and G are very small (&0.5 Pa) in both
N and NR phases compared to the SmA phase (&20 Pa).
%%%
Both G and G increase in the SmA phase when the field
is increased to 13.3 × 104 V/m and decrease again at muchhigher field (66.6 × 104 V/m). For example, in the middle

FIG. 8. (Color online) Variation of effective dielectric constant(&ef ) across N -SmA-NR phase transitions at various ac electric fields
at an angular frequency ω = 10 rad/s and strain amplitude γ = 0.05.
The frequency of the applied field is 3.11 kHz. Orientations of SmA
layers with respect to field direction are shown schematically.

of the SmA phase (i.e., T − TNI = −42◦ C) at a low field%(0.8 × 104 V/m), G & 20 Pa and increases to &32 Pa at a field4
13.3 × 10 V/m and then decreases to a small value &4 Pa
beyond 226.7 × 104 V/m. Similar behavior with temperature%%and field is also observed in the case of G .
%%%To understand the temperature variation of G and G
at various fields we simultaneously measured the effective
dielectric constant (&ef ) as a function of temperature as shownin Fig. 8. It is noticed that &ef at low field (0.8 × 104 V/m) in
N , SmA, and NR phases are comparable to the perpendicularcomponent of the dielectric constant (&⊥ ) measured in a surfacealigned planar cell [33], suggesting that the SmA layers within
the domains are oriented parallel to the field direction as shownin Fig. 8. When the field is increased to 13.3 × 104 V/m, &ef
increases in all the phases due to the partial alignment of thedirector along the field direction. However, at the same field &ef
is comparatively lower in the SmA phase than in both the N and
NR phases. For example, at the middle of the SmA temperature
range (i.e., T − TNI = −42◦ C) &ef & 12.5 whereas in both
N and NR phases it is &15. At much higher field (66.7 ×
104 V/m) &ef is almost comparable in all the phases, indicatingthat the director, and hence the layer normal, is almost parallelto the field direction. This suggests that in the intermediate
field (13.3 × 104 V/m) SmA layers (within the domains) areoriented such that the layer normals in different domains aretilted in different directions with respect to the field direction.
Such orientations of SmA layers are expected to create moredislocations, and as a result both the shear moduli can increase(in Fig. 7). At high field (66.7 × 104 V/m) the dislocation
density decreases due to the almost complete orientation of
the SmA layers (Fig. 8) and both the moduli decrease.
IV. CONCLUSIONS%

FIG. 7. (Color online) Variation of (a) storage modulus (G ) and%%(b) loss modulus (G ) across N -SmA-NR phase transitions at various
ac electric fields at an angular frequency ω = 10 rad/s and strain
amplitude γ = 0.05.

In conclusion, we have shown that strong shear thinning isdue to both the elongation of domains and the realignment of
a director within the domains in both N and SmA phases. The
domain elongation starts beyond a threshold shear rate andin the case of SmA this shear rate is about five times higher

011710-5

PHYSICAL REVIEW E 86, 011710 (2012)

J. ANANTHAIAH et al.

than in the N phase. The director orientation changes under
the application of electric field as the temperature is reduced
across N-SmA-NR phase transitions. We presented possible
layer orientations at various electric fields and showed thatthe zero-field viscoelasticity in the SmA phase is aided by thepresence of dislocations, which disappear on application ofstrong external field.

[1] P. G. de Gennes, The Physics of Liquid Crystals, 2nd ed. (Oxford
University Press, Oxford, 1993).
[2] S. Chandrasekhar, Liquid Crystals, 2nd ed. (Cambridge
University Press, Cambridge, 1992).
[3] V. V. Belyaev, Viscosity of Nematic Liquid Crystals, 1st
Indian ed. (Cambridge International Science Publishing,Cambridge, 2011).
[4] F. M. Leslie, J. Mech. Appl. Math. 19, 357 (1966).
[5] M. Miesowicz, Nature (London) 17, 261 (1935).
[6] M. Miesowicz, Bull. Acad. Pol. Sci. A 28, 228 (1936).
[7] Ch. Gahwiller, Phys. Lett. A 36, 311 (1971).
[8] Ch. Gahwiller, Mol. Cryst. Liq. Cryst. 20, 301 (1973).
[9] H. Kneppe, F. Schneirder, and N. K. Sharma, J. Chem. Phys. 77,
3203 (1982).
[10] K. Negita, Int. J. Mod. Phys. B 13, 2005 (1999).
[11] K. Negita, J. Chem. Phys. 105, 7837 (1996).
[12] Orsay Liquid Crystal Group, Mol. Cryst. Liq. Cryst. 13, 187(1971).
[13] R. F. Bruinsma and C. R. Safinya, Phys. Rev. A 43, 5377 (1991).
[14] C. R. Safinya, E. B. Sirota, and R. J. Plano, Phys. Rev. Lett. 66,
1986 (1991).
[15] J. L. Ericksen, Arch. Ration. Mech. Anal. 4, 231 (1960).
[16] T. Carlsson and K. Skarp, Mol. Cryst. Liq. Cryst. 78, 157(1981).
[17] T. Carlsson and K. Skarp, Mol. Cryst. Liq. Cryst. 104, 307(1984).
[18] J. Jadzyn and G. Czechowski, J. Phys.: Condens. Matter 13,
L261 (2001).
[19] J. Jadzyn and G. Czechowski, Phys. Rev. E 64, 052702(2001).

ACKNOWLEDGMENTS

S.D. gratefully acknowledges financial support from DST,
Government of India (Grant No. SR/NM/NS-134/2010) and
CSIR (Grant No. 03(1207)/12/EMR-II). J.A., M.R., and S.D.
gratefully acknowledge the support from UGC-CAS, Schoolof Physics.

[20] S. Bhattacharya and S. V. Letcher, Phys. Rev. Lett. 44, 414(1980).
[21] K. Negita, M. Inoue, and S. Kondo, Phys. Rev. E 74, 051708(2006).
[22] J. Ananthaiah, M. Rajeswari, V. S. S. Sastry, R. Dabrowski, andS. Dhara, Eur. Phys. J. E 34, 74 (2011).
[23] P. E. Cladis, D. Guillon, F. R. Bouchet, and P. L. Finn, Phys.
Rev. A 23, 2594 (1981).
[24] A. R. Kortan, H. V. Kanel, R. J. Birgeneau, and J. D. Litster,Phys. Rev. Lett. 47, 1206 (1981).
[25] H. A. Barnes, J. F. Hutton, and K. Walters, An Introduction to
Rheology (Elsevier, Amsterdam, 1989).
[26] M. T. Cidade, G. Pereira, A. Bubnov, V. Hamplova, M. Kaspar,
and J. P. Casquilho, Liq. Cryst. 39, 191 (2012).
[27] S. Fujii, S. Komura, Y. Ishii, and C. Y. D. Lu, J. Phys.: Condens.
Matter 23, 235105 (2011).
[28] B. Hsiao, R. S. Stein, and K. Deutscher, J. Polym. Sci., Part B:
Polym. Phys. 28, 1571 (1990).
[29] B. Schubert, N. J. Wagner, and E. W. Kaler, Langmuir 20, 3564
(2004).
[30] K. Negita, Mol. Cryst. Liq. Cryst. 300, 163 (1997).
[31] A. Kubono, K. Yoshino, T. Ninomiya, R. Akiyama, andK. Tanaka, Liq. Cryst. 29, 1089 (2002).
[32] W. H. de Jeu, Physical Properties of Liquid Crystal Materials(Gordon and Breach, New York, 1980).
[33] We measured parallel (&|| ) and perpendicular (&⊥ ) componentsof the dielectric constant in planar and homeotropic cells as afunction of temperature. We found &⊥ & 5.9 and &|| & 16.5 at
T − TNI = −45◦ C. The subscripts refer to directions in relation
to the director.

011710-6