Determination of Thermo Optical Parameters Using Image Analysis Technique in nBA: 7HB Hydrogen Bonded Liquid Crystals | Open Access Journals

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Determination of Thermo Optical Parameters Using Image Analysis Technique in nBA: 7HB Hydrogen Bonded Liquid Crystals

S. Sreehari Sastry1, K. Lakshmi Sarada2, K. Mallika2, L. Tanuj Kumar2, Ha Sie Tiong3
  1. Professor, Department of Physics, Acharya Nagarjuna University, Nagarjunanagar, India
  2. Research Scholar, Department of Physics, Acharya Nagarjuna University, Nagarjunanagar, India
  3. Professor, Department of Chemical Science, Faculty of Science, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900 Kampar, Perak., Malaysia
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In this paper, thermo optical properties of homologous series of hydrogen bonded liquid crystals: p-n alkyl benzoic acid (nBA): heptyl p - hydroxybenzoate (7HB) (where n=5 to 10) have been investigated by means of applying Image analysis technique in conjunction with Polarizing Optical Microscope. Textures of liquid crystal complexes are captured. The changes in textural features as a function of temperature are useful to compute the thermo optical properties. These microscopic textures are analysed using MATLAB software. The investigated thermo optical parameters are optical transmission, Absorption coefficient, Phase retardation, birefringence and order parameter. Experimentally, this is a simple technique to observe the behaviour of the optical parameters of different liquid crystals as a function of temperature


Liquid crystals, Hydrogen bond, Thermo optical parameter, Textures, Image analysis


Liquid crystal complexes formed through the hydrogen bonding interactions of complementary molecules are studied extensively [1-5]. The main interaction in the synthesis of such of hydrogen bonded liquid crystals is due to their thermal stability, molecular shapes and structures, high directionality and dynamics for chemical and biological processes in nature [6-9]. In recent years, liquid crystal complexes have become more important as novel materials for display applications like flat panel displays, electro optic displays, optical switches, photovoltaic cells, Fluorescent films etc [10-16]. The phase transitions and optical behaviour of the complexes are considerable properties for those applications. Liquid crystal complexes formed by the hydrogen bonds between mesogenic and non mesogenic compounds exhibit the interesting properties. Complexes of unlike molecules (mesogenic and non mesogenic) producing liquid crystals frequently involve donor molecules derived from carboxylic acids and acceptor molecules derived from pyridine, benzoates, aniline, etc [17-20]. This paper deals with homologous series of mesogenic materials: p-n alkyl benzoic acid (nBA): heptyl p - hydroxybenzoate (7HB) (where n=5 to 10). The thermo optical properties (including phase transition behaviour) are investigated using image analysis technique in conjunction with POM on MATLAB platform. There are several techniques to study the temperature dependence optical properties of liquid crystals [21-24], but they involve the technical difficulties in measuring required parameters. In image analysis technique textures of liquid crystal complexes are captured from the solid phase of the sample to the isotropic phase using POM and the changes in textural features as a function of temperature is useful to compute the thermo optical properties of samples. Image analysis technique has been developed to aid the interpretation of microscopic images and to extract as much information as possible from image objects by means of applying some computational algorithms on image data or intensity values. MATLAB R, a software product by Math Works, Inc., (Natick, MA) [25,26] is used for the analysis of liquid crystal textures. A systematic investigation on thermo optical parameters of the systems such as optical transmission, Absorption coefficient, Phase retardation, birefringence and order parameter are carried out.


The used chemical ingredients p-n alkyl benzoic acid (nBA) where n=5 to 10, heptyl p - hydroxybenzoate (7HB) are the products of Frinton laboratory, New Jersey, USA. The purity of the studied compounds is 99%. The phase transition temperatures of pure p-n alkyl benzoic acid and its complexes are p-n alkyl benzoic acid (nBA): heptyl p - hydroxybenzoate (7HB) (where n=5 to 10) can be found in [27]. The phase transition temperatures measured by us is in good agreement with the standard techniques.
A small quantity of sample is placed on a commercially available glass slide usually which will be kept in the hot stage of the Polarizing Optical Microscope (Meopta DRU 3 Model) to observe the textures of the samples. The accuracy of the temperature measurements is ± 0.10C. The thickness of the liquid crystal slide is measured using travelling microscope technique and the thickness is equal to 100 μ m.
Canon EOS Digital REBEL XS/ EOS1000D is a digital single lens reflex camera with a 10.10 mega pixel image sensor is used to record the texture images of the sample through the crossed polarizer’s of the POM. The image is having 3888X2592 pixel size depicting 24 bit tonal levels in a true colour production within the range of 0 to 255 gray levels in each three primary spectral frequency of red, green and blue separately. Thermo optical parameters of the complexes of three primary wavelengths are computed as a function of temperature using MATLAB software.


The behaviour of light with respect to temperature and material is defined in terms of thermo optical properties and are measured using optical parameters like optical transmission, Absorption coefficient, Phase retardation, Phase stability, and birefringence, order parameter. These optical properties provide important information regarding the molecular ordering, molecular dynamics and type of molecular interactions in the sample. In liquid crystal complexes the hydrogen bond interactions profoundly influence the thermal properties of liquid crystalline phases, viz., melting points, enthalpies, and thermal stability. Therefore, it is necessary to investigate the thermo optical properties of liquid crystal complexes. Thermo optical properties of liquid crystals are defined in terms of image intensity values as follows.
Optical transmittances of the mesogens are measured by computing average transmitted intensity of the image texture recorded from the crossed polarizer’s condition and given as [28]
The temperature dependent birefringence values of the samples obtained from Equation (3) are used to compute the temperature dependent order parameter of the nBA:7HB complexes. These measurements are made in the phase transition regions of Cr – Cr G - I phase of the sample and the measured order parameter values are plotted against the temperature. The order parameter (S) shown in Figure 5 is maximum in Cr – Cr G transition state and it goes on decreasing as the temperature is incremented towards the isotropic phase of the sample which has the lowest order parameter of the order of 0.15. The values of order parameter during the transition from the Cr – Cr G - I phases are in the range of 0.85 to 0.15. Here the parameters are computed purely based on gray level intensity vales of the image textures [41,42], where as in the other case the parameters are obtained based on the light transmitted intensity, molecular polarizabilities, refractive indices and densities of the sample etc [31,37,41] . Order parameter values plotted against temperature in Figure 5 also evince the different transitions in nBA:7HB mesogens.


Thermo optical properties of homologous series of hydrogen bonded liquid crystals: p-n alkyl benzoic acid (nBA): heptylp - hydroxybenzoate (7HB) (where n=5 to 10) are investigated using Image analysis technique on MATLAB plat form. As a function of temperature, the sample undergoes different phase transitions showing different textures. Textural features of the samples in relation to temperature provided the information approximately suitable to determine the optical properties of the samples. The computed thermo optical parameters all plotted against temperature well established the different transitions and their corresponding transition temperatures in nBA:7HB mesogens under investigation.


The authors gratefully acknowledge University Grants Commission Departmental Research Scheme at Level III program No. F.530/1/DRS/2009 (SAP-1), dated 9 February 2009, and Department of Science and Technology -Fund for Improving Science and Technology program No. DST/FIST/PSI –002/2011 dated 20-12-2011, New Delhi, to the department of Physics, Acharya Nagarjuna University for providing financial assistance.


  1. T.Kato, M.J.Jean, F.T.Uryu, F.Kaneuchi, and J.Chibiro, “Hydrogen – Bonded Liquid Crystals built from hydrogen – bonding donors and acceptors Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridil moieties” Liq. Cryst,, vol. 33, pp. 1311- 1317, 2006.
  2. T. Kajitani, S.Kohmoto ,M.Yamamoto and K.Kishikawa, “Liquid crystalline amides: linear arrangement of rod-like molecules by lateral intermolecular hydrogen bonding and molecular shape effect,” J. Mater. Chem., vol. 14, pp. 3449-3456, 2004.
  3. T.Kato and J.M.J. Fréchet “New approach to mesophase stabilization through hydrogen-bonding molecular interactions in binary Mixtures” ,J. Am . Chem. Soc., vol. 111, pp.8533–8534, 1989.
  4. G.W. Gray and J.W. Goodby, Smectic Liquid Crystals, Leonard Hill, Glasgow, 1984.
  5. U. Kumar, T. Kato, and J.M.J. Frechet, Use of intermolecular hydrogen bonding for the induction of liquid crystallinity in the side chain of Polysiloxanes J. Am. Chem. Soc. vol.114, pp. 6630-6639, 1992.
  6. S.J.Lee, M.You, S.W. Lee, J. Lee, J. H. Lee and J.Y. Jho. “Star-shaped supramolecular liquid crystals formed by hydrogen bonding between phloroglucinol and stilbazole derivatives with different molecular shapes” ,Liq.Cryst. vol. 38, pp.1289-1299, 2011.
  7.  A. Mohamed, Tschierske, Carsten, and PrehmMarko “Hydrogen-bonded supramolecular complexes formed between isophthalic acid and pyridine-based derivatives” Liq.Cryst, vol. 38, pp. 925-934, 2011.
  8.  S A.Jewell “Living systems and liquid crystals” Liq.Cryst, vol. 38, pp.1699–1714, 2011.
  9. Andrew G. Cook, James L. Wardell, Nicholas J. Brooks , John M. Seddon, Alfonso Martínez-Felipe and T. CorrieImrie. Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety, Carbohydrate Research” vol. 360, pp. 78-83, 2012.
  10. H.R.Brand, P.E Cladis and H. Pleiner, Symmetry and defects in the CM phase of polymeric liquid crystals Macromolecules, vol, 25, pp. 7223- 7226, 1992.
  11.  A. G Cook, U.Baumeister and C. Tschierske, Supramoleculardendrimers: Unusual mesophases of ionic liquid crystals derived from protonation of DAB dendrimers with facial amphiphilic carboxylic acids, J. Mater. Chem., vol. 15, pp.1708-1721, 2005.
  12. Haitao Wang, BinglianBaic, Fu-QuanBaia ,DongmeiPangb , Xia Ranb , ChengxiaoZhaob ,Hong-Xing Zhanga and Min Lib. Direct evidence for the effect of lateral hydrogen bonding on the smectic phase. Liq.Cryst. vol. 38, pp. 767-774, 2011;
  13.  U Mitschke, P. Buerle, The electroluminescence of organic materials, J. Mater. Chem. vol. 10, pp. 1471–1507, 2000
  14. J.W. Doane, and A. Khan Flexible Flat Panel Displays; John Wiley & Sons, Ltd: West Sussex, UK, 2005.
  15. S Sergeyev, W Pisula, Y H Geerts. “Discotic liquid crystals: a new generation of organic semiconductors” chemical society reviews vol. 36, pp. 902–1929, 2007
  16. M Petrov, B Katranchev, P.M .Rafailov, H .Naradikian, Dettlaff-Weglikowska U,Keskinova Eand Spassov T, “Phases and properties of nanocomposites of hydrogen-bonded liquid crystals and carbon nanotubes” Phisical Review E, vol. 88, pp .042503, 2013.
  17. T.Kato, H.Adachi, A. Fujishima, J.M.J Frechet, Self-Assembly of Liquid Crystalline Complexes Having Angular Structures through Intermolecular Hydrogen Bonding Chem. Lett, vol. 21, pp. 265-268, 1992.
  18. T Kato, J.M.Frechet, P.G Wilson., Takeshi Saito , Toshiyuki Uryu , Akira Fujishima , Chihiro Jin , Fumiko Kaneuchi Hydrogen-bonded liquid crystals. Novel mesogens incorporating nonmesogenic bipyridyl compounds through complexation between hydrogen-bond donor and acceptor moieties Chem. Mater. vol. 5, pp. 1094, 1993
  19.  A. J. Gopunath, T .Chitravel.C Kavitha, N.PongaliSathyaPrabu, and M. L.N Madhu Mohan, Double Hydrogen Bonded Liquid Crystals Formed by Glutaric Acid, Mol. Cryst. Liq. Cryst. vol. 547, pp. 19-32, 2013.
  20. P.A, Kumar, V.G.K.M. Pisipati,A.V. Rajeswari, and S.Sreehary Sastry, Induced smectic-G phase through intermolecular hydrogen bonding part XII#: Thermal and phase Behaviour of p-aminobenzonitrile:p-n- alkoxybenzoic acid, Z.Naturforsch. A. Vol. 57, pp. 184-189, 2002.
  21.  NejmettinAvci, ArifNesrullajev,SenerOktik, Nonlinear thermotropic and thermo-optical behaviour of planar oriented textures in nematic liquid crystals at phase transitions. Brazil. J. Phy, vol. 40, pp. 224- 227, 2010.
  22.  Shin–Tson Wu, Uzi Efron, LaVerne D. Hess, Birefringence measurements of liquid crystals, Appl. optics., vol. 23, pp. 3911- 3915, 1984.
  23.  Ivan HallerH. A., Huggins, and FreiserM. J, On the Measurement of Indices of Refraction of Nematic Liquids, Mol.Crys.Liq.Cryst, , vol,16, pp. 53- 59, 1972.
  24. KędzierskiJ,Raszewski Z, Kojdecki M. A, Kruszelnicki-NowinowskiE ,PerkowskiP,PiecekW,MiszczykE, Zieliński J, Morawiak P and Ogrodnik K, Determination of ordinary and extraordinary refractive indices of nematic liquid crystals by using wedge cells Opto-Electronics Review, vol. 18, pp. 214-218, 2010.
  25.  C Rafel. Gonzalez, E Richard. Woods, L Steven. Eddins, Digital Image Processing Using MATLAB (Gatesmark, Natick, 2009), vol.2. p.1.
  26.   C.J Solomon, T.P Breckon, Fundamentals of Digital Image Processing: A Practical Approach with Examples in Matlab, Wiley-Blackwell, Chichester, UK, 2011.
  27.  SreehariSastry S, Nageswara Rao C, Vishwam T, Mallika K and Ha sieTiong, Confirmational Studies of intermolecular hydrogen bonding through induced crystal G phase in nBA:7HBLiq.Cryst., vol. 40: pp. 932-941, 2013.
  28.  RajivManohar, Abhishek Kumar Srivastava, Jyotishman, Shukla J.P,Prajapati A. K, Bonde N.L, Dielectric, optical and thermo dynamical properties of liquid crystal sample exhibiting SmA phase, Int.J.Phys. Sci., vol. 1, pp. 147-153, 2006.
  29.  Hsin-Chung Lien. and Chih-Hua Liu, A Method of Inspecting Non-woven Basis Weight Using the Exponential Law of Absorption and Image Processing, Textile Res.J. vol. 76, pp. 547-558 2006.
  30.  Shri Singh, Liquid crystal – Fundamentals, World Scientific Publishing Co., Singapore, 2002.
  31.  C Kavitha, N PongaliSathyaPrabu, and M.L.N Madhu Mohan M.L.N, Birefringence Study in Hydrogen Bonded Complexes, Mol. Cryst.Liq.Cryst., vol. 592, pp. 163-180, 2014.
  32.  Birendra Bahadur, Liquid Crystals – Applications and uses, World Scientific, Singapore, 1993
  33. Iam-ChoonKhoo, Shin-Tson Wu, Optics and nonlinear optics of liquid crystals World Scientific, Singapore, 1993.
  34.  Shin – Tson Wu, Chapter -14 : Hand Book of Optics ( Sponsored by the Optical Society of America, McGraw-Hill Inc, New York, 1995.
  35. S Sreehari Sastry, T.Vindhya Kumari, K.Mallika, B.Gowri Sankara Rao, SieTiong Ha, and S.Lakshminarayana , Order parameter studies on EPAP Alkanoate mesogens Liq.Cryst., vol. 39, pp. 295-301, 2012.
  36.  S Sreehari Sastry., T.Vindhya Kumari, S Salma Begum., and V Venkata Rao., Investigations into effective order geometry in a series of liquid crystals. Liq.Cryst., vol. 38, pp. 277 – 285, 2011.
  37.  A.J .Gopunath, T Chitravel, C Kavitha, N PongaliSathyaPrabu, and M.L.N Madhu Mohan , Thermal, Optical, and Dielectric Analysis of Hydrogen-Bonded Liquid Crystals Formed by Adipic and Alkyloxy Benzoic Acids,Mol. CrystLiqCryst, vol. 592, pp. 63-81, 2014.
  38.  S Sreehari Sastry, Ha Sie- Tiong, B GowriSankar Rao, T Vindhya Kumari, and KMallika,Optical properties of Liquid crystals by Image analysis,Liq.Cryst, vol.39, pp. 1414-1419, 2012.
  39.  S Sreehari Sastry, Sandeep Kumar, T Vindhya Kumari, K Mallika, B GowriSankar Rao B and Ha Sie- Tiong, Liquid Crystal Parameters through Image Analysis, Liq.Cryst., vol.39, pp. 1527-1537, 2012.
  40.  S. SreehariSastry, B GowriSankar Rao, T Vindhya Kumari, K Mallika, and Ha Sie- Tiong, Novel method for order parameter of ferroelectric liquid crystals by image analysis, Liq.Cryst., vol. 40, pp. 384-390, 2012
  41.  Monika Valisko, Janos Liszi, and IstvanSzalai, Relative permittivity of a few H-bonded liquid crystals, J Mol.Liq, vol. 109, pp. 39–43, 2004.