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MEASUREMENT OF BIREFRINGENCE AND
TRANSITION TEMPERATURE OF NEMATIC LIQUID
CRYSTAL
PROJECT REPORT
SUBMITTED IN THE PARTIAL ...
DECLARATION
I, SOUVIK ROY, hereby declare that my project work on " MEASUREMENT
OF BIREFRINGENCE AND TRANSITION TEMPERATUR...
CERTIFICATE
This is to certify that the project work on " MEASUREMENT OF
BIREFRINGENCE AND TRANSITION TEMPERATURE OF NEMAT...
ACKNOWLEDGEMENTS
First and foremost I would like to thank the Almighty for his grace
upon me, without which, I would not h...
CONTENTS
1. INTRODUCTION
2. ORDER PARAMETER
3 TYPES OF LIQUID CRYSTAL
3.1 CALAMITIC
a) NEMATIC
b) TWISTED NEMATIC
c) SMECT...
a) SAMPLE
b) ORGANIC NAME
c) TRANSITION TEMPERATURE
8. SOMETEXTURES OF LIQUID CRYSTAL UNDERNIKONPOLARISING
MICROSCOPE.
a) ...
1. INTRODUCTION :
The study of liquid crystals began in 1888 when an Austrian botanist named Friedrich
Reinitzer observed ...
3. TYPES OF LIQUID CRYSTAL :
Depending on the shape of the molecules thermotropic liquid crystal can be classified into
th...
b) Twisted nematic phase: InthisCholesteric ortwistedphase alongwithlongrange
orientational orderspatial variation of dire...
the layer plane. Within the layers, the centers of gravity of the molecules are
ordered at random. Thus, smectics A posses...
uniaxial, and show optical activity and selective reflection similar to the
cholesterics.
iv) ANTICLINIC :Here the long ax...
b) BIREFRINGENCE: Liquid crystals are found to be birefringent, due to
their anisotropic nature. That is, they demonstrate...
6. MEASUREMENT OF CELL THICKNESS :
 The liquid crystal cell is kept under spectrometer reflecltion probes, which consist ...
 FORMULA USED : -
d= (λn-λm)/λn λm*(n - m)/2
where n & m are the peaks and λn, λm are the corresponding wavelength.
We ca...
8. SOME TEXTURES OF LIQUID CRYSTAL UNDER NIKON
POLARISING MICROSCOPE :
we place the liquid crystal sample 8OCB under Nikon...
 Textures at isotropic phase : (at temperature 82 ͦ)
 Textures fromisotropic to nematic transition : (at temperature 78 ...
 Textures at nematic phase : ( at temperature 72 ͦ)
 Textures fromnematic to smectic transition : (at temperature 66 ͦ)
 Textures at smectic phase: (at temperature 58 ͦ)
d) HERE IS SOMETEXTURES AT PURE SMECTICPHASE: (AT TEMPERATURE 62 ͦ
WITH...
e) SOME TEXTURES AT SMECTIC TO CRYSTAL TRANSITION (AT
TEMPERATURE 54 ͦ WITH 20X OPTICAL ZOOM) :
9. MEASUREMENT OF BIREFRINGENCE : -
The birefringence of a uniaxial liquid crystal can be measured by two techniques.
 In...
i) APPERATUS :
a) He –Ne source.
b) Optical bench on a shelf with a hole for passing the light.
c) Glan-thompson polarizer...
Is = I0 Sin²(πΔn/λ)
And birefringence is given by,
∆n=(λ/πd)arcSin (√(Is/I0) .
b) Calculation & graph :-
 measuring the t...
 THE GRAPH FOR COMPAREING THEEXPERIMENTAL VALUEAND
THEORITICAL VALUE:
c) RESULTS :
After draw a plot between birefringenc...
 EXPERIMENTAL VALUES OF TRANSITIONTEMPERATURE:
FIRST TRANSITION TEMPERATURE : 80.208 ͦ
(DENOTES ISOTROPIC TO NEMATIC TRAN...
PROJECT FINAL PAPER
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PROJECT FINAL PAPER

  1. 1. MEASUREMENT OF BIREFRINGENCE AND TRANSITION TEMPERATURE OF NEMATIC LIQUID CRYSTAL PROJECT REPORT SUBMITTED IN THE PARTIAL FULFILLMENT OF THE ACADEMIC REQUIREMENT FOR THE AWARD OF MASTER OF SCIENCE IN PHYSICS BY SOUVIK ROY 13PHMP09 IN GUIDANCE Dr. SURAJIT DHARA AssociateProfessor, Schoolof Physics
  2. 2. DECLARATION I, SOUVIK ROY, hereby declare that my project work on " MEASUREMENT OF BIREFRINGENCE AND TRANSITION TEMPERATURE OF NEMATIC LIQUID CRYSTAL" submitted to School Of Physics, University of Hyderabad, Hyderabad, for partial fulfillment of the Degree of MASTER OF SCIENCE IN PHYSICS has been carried out by me under the supervision of Dr. SURAJIT DHARA, School Of Physics, University Of Hyderabad. To the best of my knowledge, this work has not been submitted for any other degree in any university. SOUVIK ROY M.Sc., PHYSICS Reg.No: 13PHMP09 UNIVERSITY OF HYDERABAD
  3. 3. CERTIFICATE This is to certify that the project work on " MEASUREMENT OF BIREFRINGENCE AND TRANSITION TEMPERATURE OF NEMATIC LIQUID CRYSTAL " is a bonafide work done by Mr. SOUVIK ROY bearing the Reg.No:13PHMP09 under my guidance in partial fulfillment of the requirements for the award of degree of MASTER OF SCIENCE IN PHYSICS and submitted to School Of Physics, University Of Hyderabad. This work has not been submitted for any other degree in any University. DR. SURAJIT DHARA SUPERVISOR School Of Physics DEAN School Of Physics
  4. 4. ACKNOWLEDGEMENTS First and foremost I would like to thank the Almighty for his grace upon me, without which, I would not have been able to complete this project. I am indebted to my parents for their continuous encouragement. I would like to express my sincere gratitude to my project supervisor Dr. SURAJIT DHARA for his generous nature, infinite patience and helpful guidance. I will always remember his suggestions and practice his advices in both my professional and personal life. I am Highly thankfull to Mr. VENKATA SAI DASARI for constant help and encouragement during the project. I take the opportunity to thank all my labmates like M.V RASNA, RASMITA SAHOO,ZUNAID AHMED for their co-operation and suggestions for my project work. SOUVIK ROY 13PHMP09 PLACE: DATE: UNIVERSITY OF HYDERABAD 6TH MAY, 2015 HYDERABAD-500046
  5. 5. CONTENTS 1. INTRODUCTION 2. ORDER PARAMETER 3 TYPES OF LIQUID CRYSTAL 3.1 CALAMITIC a) NEMATIC b) TWISTED NEMATIC c) SMECTIC PHASES i) SMECTIC A ii) SMECTIC C iii) SMECTIC C* iv) ANTICLINIC 4. SOME OPTICALPROPERTIES OF LIQUID CRYSTAL: a) Refractive index. b) Birefringence. 5. MAKING OF LIQUID CRYSTAL CELL: 6. MEASUREMENT OF THICKNESS OF THE CELL: 7. LIQUID CRYSTAL SAMPLE FOR EXPERIMENT :
  6. 6. a) SAMPLE b) ORGANIC NAME c) TRANSITION TEMPERATURE 8. SOMETEXTURES OF LIQUID CRYSTAL UNDERNIKONPOLARISING MICROSCOPE. a) APPARATUS b) PROCEDURE c) TEXTURE IN DIFFERENT PHASE TRANSITIONS d) SOME TEXTURE WITH DIGITAL CAMERA WITH 10X AND 20X OPTICAL ZOOMAT TEMPERATURE 62 AND 54. 9. MEASUREMENT OF BIREFRINGENCE a) INTENSITYMEASUREMENTTECHNIQUE i)APPARATUS. ii)PROCEDURE. iii)WORKING FORMULA. b) CALCULATIONS AND GRAPH c) RESULTS . 10. REFERENCES.
  7. 7. 1. INTRODUCTION : The study of liquid crystals began in 1888 when an Austrian botanist named Friedrich Reinitzer observed that a material known as cholesteryl benzoate had two distinct melting points (419K and 552K) .In this experiments, Reinitzer increased the temperature of a solid sample and observed the crystal changing into a hazy liquid. Further increasing of temperature that sample again changes to transparent liquid .they are found among organic compounds with molecular shape anisotropy.they are classified into two types namely thermotropic and lyotropic.thermotropic liquid crystal exhibit mesophases as a function of its concentration in solvent.conventional liquid crystals are mostly made of rod and disc type of molecules. 2. ORDER PARAMETER : Liquid crystals possess some degree of orientational order To quantify how much order is present in a material an order parameter (S) is defined.Liquid crystal molecules possess orientational order. The direction of preferred orientation in a liquid crystal is called the director .The order parameter is given as follows S= ½ <3cos²θ – 1> where, θ is the angle made by each molecule with the director axis denoted by n.
  8. 8. 3. TYPES OF LIQUID CRYSTAL : Depending on the shape of the molecules thermotropic liquid crystal can be classified into three categories. i)calamitic. ii) Discotic. iii) bend core type. Which basically composed with rod like,disc like and bent core molecules. 3.1 calamitic liquid crystal:- it consist of rigid cores with flexible side chains.there are many mesophases formed by calamitic mesogens. a) Nematic phase: This phase ischaracterizedbythe moleculesthathave nopositional orderbut tendto orientinthe same directioni.e.,alongthe director.
  9. 9. b) Twisted nematic phase: InthisCholesteric ortwistedphase alongwithlongrange orientational orderspatial variation of directorisalsoexistwhichcauseshelical structure. c) SMECTICPHASES : These phases shows orientational order along with positional order.the molecules preferably pointing in one direction. Just like in the nematic phases.in the layer the centre of mass of the molecules are random i.e liquid like.there are several different types of smectic phases. i) Smectic A : In smectic A (SmA) phases, on average, the molecules are parallel to one another and are arranged in layers, with the long axes perpendicular to
  10. 10. the layer plane. Within the layers, the centers of gravity of the molecules are ordered at random. Thus, smectics A possess the one-dimensional quasi long- range positional order and within the layers molecules show a relatively high mobility. The layer thickness is equal to the molecule length. SmA LCs are optically positive and uniaxial with the optic axis parallel to the molecular long axes. ii) Smectic c :. For The structure of the smectic C (SmC) liquid crystals is closely related to the structure of the SmA. The molecules are arranged in layers, but the long axes of the molecules are tilted to the layers planes.some materials the tilt angle is constant but for others it is temperature dependent. The centers of gravity of the molecules are randomly ordered and the moleculesare free to rotate around their long axes. SmC phases are optically biaxial. iii) SMECTIC C* : The SmC* phase is similar to the SmC phase but consists of the chiral molecules, which rotate the direction of the director projection on the layer plane from one layer to the next. The twist axis of the SmC* is perpendicular to the layers. Therefore, these phases appear optically positive
  11. 11. uniaxial, and show optical activity and selective reflection similar to the cholesterics. iv) ANTICLINIC :Here the long axis of molecules make an angle with the layer normal . 4. SOME OPTICAL PROPERTIES OF LIQUID CRYSTAL : a) REFRACTIVE INDEX : In liquid crystal the speed of light is parallel to the direction is different from the perpendicular direction.nematic phase has two principal refractive index for ordinary and extraordinary rays.
  12. 12. b) BIREFRINGENCE: Liquid crystals are found to be birefringent, due to their anisotropic nature. That is, they demonstrate double refraction (having two indices of refraction). In the following diagram, the blue lines represent the director field and the arrows show the polarization vector. ∆n= ne – no. Where ne and no are the refractive index for extraordinary and ordinary Rays . 5. MAKING OF A LIQUID CRYSTAL CELL : a) Firstwe cut the slidesaround1.5cm² inarea withspecial diamondcutter. b) Thenwe washthe slideswithsoapsolutionandstartoursolicationprocess. Firstwe solicate the slideswithbenzenefor30 mints,andthenwithasetone for30 minutes and afterthat withdistilledwaterfor30 mints. c) Aftersolicationwe dryupour slideswithdryerandNitrogengasforbubble removing. d) Afterbubble removingwe use ouralignmentlayerSC7942 on the slidesandputit inthe spin coater machine andputin a furnace at 180 ͦc for 45 mints, rubbing followsafter the furnace work. e) Afterrubbingstickingwith8µmsample withglue.andhasto keepforsome time underUV ray. f) Cells are prepare foruse.
  13. 13. 6. MEASUREMENT OF CELL THICKNESS :  The liquid crystal cell is kept under spectrometer reflecltion probes, which consist of optical fibre.it is illuminated through outer six fibres of probes. And reflected light is collected by central fibre and fed to spectrometer.  Then view the spectrum in the computer using a software called spectrasuite .
  14. 14.  FORMULA USED : - d= (λn-λm)/λn λm*(n - m)/2 where n & m are the peaks and λn, λm are the corresponding wavelength. We can get the values of λ’s accurately using the software. 7. LIQUID CRYSTAL SAMPLE FOR EXPERIMENT: a) SAMPLE :- 8OCB b) ORGANIC NAME :- 4-Octyloxy-4’-cyanobiphenyl c) TRANSITION TEMPERATURE :- i) CRYSTAL TO SMECTIC - 54 ͦ C ii) SMECTIC(A) TO NEMATIC - 67 ͦ C iii) NEMATIC TO ISOTROPIC - 80 ͦ C
  15. 15. 8. SOME TEXTURES OF LIQUID CRYSTAL UNDER NIKON POLARISING MICROSCOPE : we place the liquid crystal sample 8OCB under Nikon polarising microscope,and with varing the temperature and take some pictures of the sample at different transition temperature. a) APPARATUS REQUIRED : i) Liquid crystal sample holder ii) Temperature controller. iii) Nikon porarising microscope. iv) Digital camera with 10x and 20x optical zoom. v) Computer Pc. b) PROCEDURE: i) First take the sample 8OCB in between the liquid crystal slide. ii) Stick it with temperature resistant cellotape with the sample holder. iii) Sample holder is connected with the temperature controller. iv) Increase the tempreture beyond 80 ͦ , and then cool it down . v) Take the textures at 10x and 20x optical zoom by digital camera at the transition temperatures. c) TEXTURES AT DIFFERENTPHASETRANSITION:
  16. 16.  Textures at isotropic phase : (at temperature 82 ͦ)  Textures fromisotropic to nematic transition : (at temperature 78 ͦ )
  17. 17.  Textures at nematic phase : ( at temperature 72 ͦ)  Textures fromnematic to smectic transition : (at temperature 66 ͦ)
  18. 18.  Textures at smectic phase: (at temperature 58 ͦ) d) HERE IS SOMETEXTURES AT PURE SMECTICPHASE: (AT TEMPERATURE 62 ͦ WITH 10X OPTICAL ZOOM)
  19. 19. e) SOME TEXTURES AT SMECTIC TO CRYSTAL TRANSITION (AT TEMPERATURE 54 ͦ WITH 20X OPTICAL ZOOM) :
  20. 20. 9. MEASUREMENT OF BIREFRINGENCE : - The birefringence of a uniaxial liquid crystal can be measured by two techniques.  Intensity measurement technique.  Phase modulation technique. In my experiment i use only intensity measurement technique. a) INTENSITYMEASUREMENTTECHNIQUE: Using dc intensity measurement technique we can measure the birefringence.the optical set up is shown in the figure.
  21. 21. i) APPERATUS : a) He –Ne source. b) Optical bench on a shelf with a hole for passing the light. c) Glan-thompson polarizers. d) Detector. ii) EXPERIMENTAL PROCEDURE:  The plane polarised light after the GT polariser passes through the sample, in which the rubbing direction is 45 ͦ with respect to the first polariser. The transmitted light then passes through the second polariser and after that goes to a detector.the detector output is connected to keithly dc voltmeter for measurement of output intensity.  the temperature of the sample then controlled by temperature controller called instec.  For measurement of temperature dependent birefringence,temperature is varied with finite step and the corresponding intensity is measured by the detector.  All the measurement is controlled by the computer and with the help of a software called LabVIEW. We place the liquid crystal sample between two crossed polariser.and rubbing direction makes an angle φ with polariser.Assuming the analyser and polariser is in x and y direction and light propagates in z direction. iii) WORKING FORMULA: If the intensity of light after the first polariser is I0 , then intensity at the detector is given by, I= I0 Sin²(2φ)Sin²(πΔn/λ) Setting φ=45 ͦ , the intensity at the detector is given by,
  22. 22. Is = I0 Sin²(πΔn/λ) And birefringence is given by, ∆n=(λ/πd)arcSin (√(Is/I0) . b) Calculation & graph :-  measuring the temperature and corresponding intensity, Using the software LaBVIEW .  Calculate the birefringence for each intensity.  Plot a graph in origin software with temperature is along x axis. And birefringence along y axis .  THE GRAPH BETWEEN BIREFRINGENCEAND TEMPERATURE:
  23. 23.  THE GRAPH FOR COMPAREING THEEXPERIMENTAL VALUEAND THEORITICAL VALUE: c) RESULTS : After draw a plot between birefringence and temperature in origin software i can realise how the birefringence changes with temperature.with increases the temperature birefringence decreases.  When cooling from temperature 84, ͦI saw the first transition occurs in the graph at temperature near about 80.208 ͦ . it denotes some phase is changes.and we know the theoretical transition temperature for isotropic to nematic transition is near about 80 ͦ,which is nearer to our experimental value. So the transition of phase is isotropic to nematic.  The second transition occurs at temperature near about 65.947 ͦ. Which is close to our theoretical nematic to smectic transition temperature 67 ͦ. So the transition phase is nematic to smectic.  And also my graph is approximately the same to the graph which is plotted with the theoretical values.
  24. 24.  EXPERIMENTAL VALUES OF TRANSITIONTEMPERATURE: FIRST TRANSITION TEMPERATURE : 80.208 ͦ (DENOTES ISOTROPIC TO NEMATIC TRANSITION) CORRESPONDING BIREFRINGENCE : 0.0823 SECOND TRANSITION TEMPERATURE : 65.947 ͦ (DENOTES NEMATIC TO SMECTIC TRANSITION ) CORRESPONDING BIREFRINGENCE : 0.168 10. REFERENCES:  Liquidcrystal binarymixtures8CB+8OCB:critical behaviouratthe smecticA–nematic transitionM.B. SIED, D. O. LO´ PEZ*, J. Ll. TAMARITand M. BARRIODepartamentde FÌ´sica i EnginyeriaNuclear,E.T.S.E.I.B.UniversitatPolite`cnicade Catalunya,Diagonal647, 08028 Barcelona,Catalonia,Spain(Received16December2000; accepted27 June 2001).  M. Cardona, in Solid State Physics, edited by F. Seitz, D. Turnbull, and H. Ehrenreich (Academic, New York, 1969), Suppl. 11.  Coupling between Orientational and Translational Order in a Liquid Crystal department of physics and Astronomy, State University of New York at &Buffalo, Amkerst, New York 14260, Khoon-Cheng Lim and John T. Ho.  Tharmal & spectrophotometric analysis of liquid crystal 8CB/8OCB mixtures. Sukrii ozgan,Mustafa okumus,sociedade brasileira de fisika 2011.  Order of phase transitions and tricriticality in mixtures of octyloxycyanobiphenyl and nonyloxycyanobiphenyl liquid crystals: A high-resolution study by adiabatic scanning calorimetry . George Cordoyiannis, Chandra Shekhar Pati Tripathi, Christ Glorieux, and Jan Thoen Phys. Rev. E 82, 031707 – Published 22 September 2010.  Evolutionof the isotropictonematicphase transitioninoctyloxycyanobiphenyl+aerosil dispersionsA.Roshi andG. S. Iannacchione Departmentof Physics,WorcesterPolytechnic Institute,Worcester,Massachusetts01609, USA P. S. CleggandR. J. Birgeneau Department of Physics,Universityof Toronto,Toronto,OntarioM5S 1A7, Canada (Dated:February2, 2008)

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