International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 5, Issue 3, March 2016
ISSN 2319 - 4847
Optical Behavior of Rhodamine B Dye Doped
Nematic Liquid Crystal E-24
Preeti Porov1, Vishal Singh Chandel2, Rajiv Manohar3
1
Department of Physics, Integral University, Lucknow-226026, India
2
Department of Physics, Integral University, Lucknow-226026, India
3
Department of Physics, Lucknow University, Lucknow-226007, India
ABSTRACT
The optical properties of rhodamine B dye doped nematic liquid crystal mixture E-24 have been investigated in temperature
range340C to 570C. The variations in refractive indices, order parameter, birefringence of dye doped sample at different
temperatures have been discussed. The results indicate that doped sample has a less refractive index and a higher order
parameter as compared to the pure sample. The birefringence of the guest-host mixture is also less than that of the pure
nematic E-24.
Keywords: Refractive Indices, Nematic Liquid Crystal, Dye doped liquid crystal, Order parameter, Birefringence.
1. INTRODUCTION
Liquid crystals have attracted much attention from researchers because of their optical non linearity and very rapid
optical response [1]-[5]. During last forty years a lot of research and development has been done in the field of liquid
crystals (LCs). Nematic liquid crystals (NLC) are the most commonly used LC materials in the modern display industry
[6], [7]. The most important property of a liquid crystal which governs almost all its physical properties is its
orientational order [8]-[15]. The optical anisotropy is an important property and is very useful in display devices, which
also governs the thickness of the liquid crystal layer to be used in such devices. Study of optical behavior of liquid
crystals is thus important. For practical applications the liquid crystal should have a low birefringence and high order
parameter [16]. A single LC compound cannot fulfill all the requirements of suitable parameters for the displays.
Therefore guest–host mixtures of LCs have been used because of their potential application in displays devices [17].
Dye doped liquid crystalline systems have indeed been the subject of intense studies in recent decades [18],[19]. The
addition of absorbing dyes to NLCs, introduces new orienting mechanisms [20], [21]. In a mixture of LC and dye, the
collective orientation of the LC molecules under the action of an electric field influences that of the dye molecules. This
phenomenon is called Guest-host interaction. In guest host displays the liquid crystalline materials used are the
solutions of dye in pure liquid crystal. When dyes are dissolved in the liquid crystals, they take up an orientation such
that all the long axes lie in the same direction as that of the molecules of liquid crystal. If the dye molecule is long, it’s
ordering can be quite high as compared to the ordering found in the liquid crystal. The reason of this is the reduction
in thermal motion for the longer dye molecule. The long axis of the dye molecule does not absorb light very much while
the axis orthogonal to the long molecular axis of the dye molecules absorbs more light than the shorter axis. Hence the
presence of the dye changes various properties of liquid crystals up to a great extent. The properties which can be
varied with the help of doping dye in liquid crystals are dielectric permittivity, dielectric loss, optical transmittance,
order parameter and birefringence etc. It has been observed that doping with a small amount of dye decreases the
required threshold of molecular reorientation in dye doped liquid crystal. This phenomenon has potential application in
holographic date storage. Birefringence property and its dependency on molecular reorientation also play an important
role in understanding the molecular mechanism. Various studies have been done to study the effects of dye on the
dielectric and optical properties of liquid crystals [22]-[27]. The refractive indices, order parameter, optical
birefringence and optical transmittance for pure nematic mixture E-24 and E-24 doped with anthraquinone dye have
already been published by our group [28].
This present study reports the effect of rhodamine B dye on some optical parameters of nematic mixture E-24 The
refractive indices, order parameter, birefringence of dye doped sample have been measured for dye-doped LC and
behavior of these parameters with variation in temperature have been discussed.
Volume 5, Issue 3, March 2016
Page 94
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 5, Issue 3, March 2016
ISSN 2319 - 4847
2. EXPERIMENTAL DETAILS
The liquid crystal used E-24 was supplied by BDH, England. It was used without further purification. The transition
schemes of the pure sample is as follows
-50 C
540 C
Crystal 
 Nematic 
 Isotropic
The transition schemes of the dye doped sample is
Unknown
520 C
Crystal  Nematic 
 Isotropic
Dyes used in the experiment rhodamine B was obtained from Thomas Baker. Its chemical name and composition is
given in figure 1.
N-[9-(2-Carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]N-ethylethanaminium chloride
Chemical Composition: C28 H31 ClN2 O3
Figure1 Structure of dye used for present study.
The dye doped sample of E-24 was prepared in the lab by dispersion of dye under investigation at a concentration of
about 2% wt/wt in the liquid crystal host material.
The measurement of the ordinary refractive index (no) and the extraordinary refractive index (ne) with the help of
Abbe’s refractometer and wedge method have been discussed in our earlier papers [16], [28].
3. THEORY (ORDER PARAMETER)
As a homogeneously aligned nematic sample behaves like a uniaxial crystal, the relation between macroscopic order
parameter (Q) and the refractive indices parallel and perpendicular to the director of molecular alignment may be given
as:
2
n||  n  Q.n
3
(1)
1
(2)
n  n  Q.n
3
Where n is the average refractive index and n is the birefringence corresponding to complete alignment and for
uniaxial crystal n || = ne, n= no From the above equations 1 and 2, we get
n n
n n
n
(3)
Q  ||   e o 
n
n
n
Volume 5, Issue 3, March 2016
Page 95
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 5, Issue 3, March 2016
ISSN 2319 - 4847
where, n=ne-no. The value of macroscopic order parameter Q=1 shows complete order of the sample at absolute
temperature, that is at 0K, n=n. Thus the macroscopic order parameter Q has been obtained by extrapolating n for
T = 0K. This extrapolation is done on the linear portion of the graph drawn between the birefringence (n) versus ln(1T/Tc) as has been reported by our group [28].
4. RESULT AND DISCUSSION
It is clear from the figure 2 that in the isotropic phase, the refractive index decreases with an increase in temperature
like other normal liquid crystals but the ordinary and extraordinary refractive indices (n o, ne) of the guest-host mixture
are slightly less than that of the pure nematic sample [29 ]. The nematic-isotropic transition temperature of the sample
E-24 as reported earlier was 540C, while that of the guest-host mixture is 520C. At the transition temperature the values
of refractive indices change abruptly. The change in transition temperature of the guest-host mixture is approximately
20C which is because of the presence of the dye molecules as an impurity in the nematic host. A similar type of
behaviour has been reported for other nematic host [30].
Figure 2 Variation of refractive indices with temperature for dye doped sample.
The variation of the macroscopic order parameter (Q) for dye doped nematic E-24 with temperature is shown in figure
3.
Figure 3 Variation of order parameter with temperature for dye doped sample E-24.
It may be seen from the figure that the order parameters of dye doped also decreases with increase in temperature and
changes abruptly at the nematic-isotropic transition 520C. The macroscopic order parameter of the guest-host mixture
is slightly greater than that of the pure nematic E-24 as reported earlier [28].
The variation of birefringence (δn) of dye doped nematic E-24 with temperature is shown in figure 4.
Volume 5, Issue 3, March 2016
Page 96
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 5, Issue 3, March 2016
ISSN 2319 - 4847
Figure 4 Variation of optical birefringence with temperature for the dye doped sample E-24.
Figure 4 shows that birefringence becomes zero at temperatures 520C for the dye doped sample mixture, which
indicates the isotropic phase of the guest-host mixture. In the nematic region, the birefringence decreases with an
increase in temperature. The birefringence of the guest-host mixture is also less than that of pure nematic E-24 as
reported previously [27], [31].
5. CONCLUSIONS
It may be concluded that optical properties such as refractive indices order parameter, birefringence show improvement
with the addition of dye in pure nematic E-24.The values of refractive indices and birefringence decreases and order
parameter increases with the addition of dye. Hence, a liquid crystal can be optimized by doping a suitable amount of
dye.
REFERENCES
[1]. Yablonskil, S.V., Nakayama, K., Okazaki, S., Ozaki, M., Yoshino, K., Palto, S.P., Baranovich, M.Y., And
Michailov S.A.J., “Control Of The Bias Tilt Angles In Nematic Liquid Crystals,” Appl. Phys., 85, 2556–2561,
1999.
[2]. Jwell, S.A., Taphouse, T.S., Sambles, J.R., “Rapid Switching In A Dual-Frequency Hybrid Aligned Nematic
Liquid Crystal Cell,” Appl. Phys. Lett., 87, 021106-1–3, 2005.
[3]. Manzo, C., Paparo, D., Marrucci, L., Janossy, I., “ Spin-To-Orbital Optical Angular Momentum Conversion In
Liquid Crystal “Q-Plates,”Classical And Quantum Applications, Phys. Rev. E., 73, 051707-1–14, 2006.
[4]. Huang, C.Y., Hsieh, C.T., Tian, J.R., “Electro-Optical Response Of The In-Plane Switching Liquid Crystal Device
Fabricated Using Two-Easy-Axes Substrate,” Optics Express, 14, 9931–9938, 2006.
[5]. R. Manohar, Abhishek Kumar Srivastava, Abhishek Kumar Misra, “Electro-Optical Behavior for Dye-Doped
FLC,” Soft Materials, 8(1), 1–13, 2010.
[6]. S. Marino, M. Castriota, V. Bruno, E. Cazzanelli, G. Strangi, C. Versace, N. Scaramuzza, J., “Changes Of The
Electro-Optic Response Of Nematic Liquid Crystal Cells Due To Inserted Titania-Vanadia Films,” Appl. Phys. 97,
013523, 2005
[7]. S.P. Yadav, K.Kr. Pandey, A.Kr. Misra, R. Manohar, “Electro-Optical Behavior Of Dye Doped Nematic Liquid
Crystal,” Acta Physica Polonica A,119, 2011.
[8]. H. Ozbek, S. Ustunel, E. Kutlu, M.C. Cetinkaya, “A Simple Method to Determine High-Accuracy Refractive
Indices of Liquid Crystals and the Temperature Behavior of the Related Optical Parameters Via High-Resolution
Birefringence Data,” Journal Of Molecular Liquids 199, 275–286,2014.
[9]. M.S. Zakerhamidi, Z. Ebrahimi, H. Tajalli, A. Ghanadzadeh, M. Moghadam, A. Ranjkesh, “Refractive Indices and
Order Parameters Of Some Tolane-Based Nematic Liquid Crystals,” Journal Of Molecular Liquids 157, 119–124,
2010.
[10]. V.G.K.M. Pisipati, D. Madhavi Latha, P.V. Datta Prasad, G. Padmaja Rani, “ Order Parameter Studies From
Effective Order Geometry In A Number Of Liquid Crystals Of Different Homologous Series,” Journal Of
Molecular Liquids 174,1-4,2012
[11]. P. Pardhasaradhi, P.V. Datta Prasad, D. Madhavi Latha, V.G.K.M. Pisipati, G. Padmaja Rani, “Orientational
Order Parameter Studies in Two Symmetric Dimeric Liquid Crystals – An Optical Study,” Phase Transitions 85,
12,1031–1044,2012
[12]. M.S. Zakerhamidi, H. Rahimzadeh, “Order Parameters and Refractive Indices of Some Cyano-Benzoate Nematic
Liquid Crystals with High Transition Temperatures,” Journal Of Molecular Liquids 172, 41–45, 2012.
Volume 5, Issue 3, March 2016
Page 97
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 5, Issue 3, March 2016
ISSN 2319 - 4847
[13]. M.S. Zakerhamidi, M.H. Majles Ara, A. Maleki, “Dielectric Anisotropy, Refractive Indices And Order Parameter
of W-1680 Nematic Liquid Crystal,” Journal Of Molecular Liquids 181, 77–81,2013
[14]. Sangita Patari, T.K. Devi, Aparna Nath, “Studies Of Optical Texture, Birefringence, Order Parameter,
Normalized Polarizability and Validation of the Four-Parameter Model Of A Thermotropic Mesogen 7OAOB,”
Journal Of Molecular Liquids 215, 244–252,2016.
[15]. C.S.V.S. Murthy, P. Pardhasaradhi, V.G.K.M. Pisipati, P.V. Datta Prasad, “Phase Transitions From Density And
Order Parameter From Polarisabilities In Symmetric Dimeric Liquid Crystals,” Liquid Crystals Today, 25, 1, 2–
9,2016.
[16]. V.S. Chandel_, R. Manohar And J.P. Shukla Refractive Indices, Order Parameter And Density Study Of
BKS/B07 Nematic Liquid Crystal,” Analele Universităńii Din Bucuresti: 20, 02, 155 – 163,2011.
[17]. R. Muenster, M. Jarasch, X. Zhuang, Y.R. Shen, “Dye-Induced Enhancement of Optical Nonlinearity in Liquids
and Liquid Crystals,” Phys. Rev. E 78, 42, 1997.
[18]. C. Motoc, G. Iacobescu, “Birefringence Of Azo-Dye Doped Nematic Liquid Crystals” Journal Of Optoelectronics
And Advanced Materials, 8, 1, 295 – 298,2006.
[19]. S. Shoarinejad, M. S. Zakerhamidi, “Ordering Behavior and Linear Dichroism of Pure and Doped Liquid Crystals
Mol. Cryst. Liq. Cryst., Vol. 613: Pp. 149–155, 2015.
[20]. P. Klysubun, G. Indebetouw Transient And Steady State Photorefractive Responses In Dye Doped Nematic Liquid
Crystal Cells” J. Appl. Phys. 91, 897,2002.
[21]. S. Ghosh, G.O. Carlisle, “Carbon Nanotube Enhanced Diffraction Efficiency in Dye-Doped Liquid
Crystal,” J. Mat. Sci. Mat. Elect. 16, 753, 2005.
[22]. S. Ozder, M. Okutan, O. Koysal, H. Goktas, S.E. San, “Effect of an Azo Dye (DR1) On the Dielectric Parameters
of A Nematic Liquid Crystal System,” Physica B 390, 101–105,2007.
[23]. Y. S. Suleiman, S. Ghosh, M. E. Abbasov, G. O. Carlisle, “Electric Field Enhancement and Modulation Of
Permanent Grating Diffraction In Dye And Carbon Nanotube-Doped Liquid Crystal,” J. Mat.Sci. Mat. Elect. 19(7),
662, 2008.
[24]. R. Manohar, S. Manohar, V. S. Chandel, “Dielectric Behaviour of Pure and Dye Doped Nematic Liquid Crystal
BKS/B07,” Materials Sciences and Appl. 2, 839-847, 2011.
[25]. Abhishek Kumar Misra, Pankaj Kumar Tripathi, Rajiv Manohar, “Changes In Material Parameters for Dye-Doped
Ferroelectric Liquid Crystal,” Phase Transitions 1-10, 2012.
[26]. K. Tagashira, H. Yoshida, A. Fujii, M. Ozaki, “ Photoinduced Polarization-Independent Refractive Index
Modulation Using Azo-Dye Doped Liquid Crystal,” Mol. Cryst. Liq. Cryst., 543, 117/[883]–122/[888], 2011.
[27]. S. Kaur, H. Liu, J. Addis, C. Greco, A. Ferrarini, V. Görtz, J. W. Goodby, H. F. Gleeson, “The Influence Of
Structure On The Elastic, Optical And Dielectric Properties Of Nematic Phases Formed From Bent-Core
Molecules,” J. Mater. Chem. C, 1, 6667-6676, 2013.
[28]. V. S. Chandel, S. Manohar, J. P. Shukla, R. Manohar, “Optical Studies of a Pure and Dye Doped Nematic Liquid
Crystal E-24,” Transactions On Electrical And Electronic Materials, 13, 5, 221-224,2012.
[29]. D. Bauman, “Optical and Thermodynamic Properties of Mixtures of Pleochroic Dye With Some AlkylCyanobiphenyl Liquid Crystals,” Mol. Cryst. Liq. Cryst. 172, 41, 1989.
[30]. Arif Nesrullajev, “Thermotropic, Refracting and Birefringent Properties In Homogeneous Mixtures of 4-N-Alkyl4′-Cyanobiphenyl Mesogens,” Journal Of Molecular Liquids 215, 503–51, 2016.
[31]. C. Motoc, G. Iacobescu, “Birefringence of Azo-Dye Doped Nematic Liquid Crystalsjournal Of Optoelectronics and
Advanced Materials,” 8, 1, 295 – 298, 2006.
AUTHOR
Preeti Porov received her B.Sc. and M.Sc. degrees in Physics from Rohilkhand University in 1994 and
1996 respectively. She is currently pursuing her Ph.D. from Integral University, Lucknow (India). Her
area of interest in research is “Optical and Dielectric properties of pure and dye doped liquid crystal.
Vishal Singh Chandel received his M.Sc. from University of Lucknow, Lucknow, U.P., India in 1998.
His research interests include dielectric properties of doped liquid crystals and Alkali Titanates.
Rajiv Manohar received his M.Sc. from University of Lucknow, Lucknow, U.P., India in 1992. His
research interests include dielectric and electro-optical properties of nano particle, polymer and dye
doped liquid crystals.
Volume 5, Issue 3, March 2016
Page 98