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Chapter 2: Liquid Crystals States between crystalline and isotropic liquid

Chapter 2: Liquid Crystals States between crystalline and isotropic liquid. Liquid Crystals, 1805-1922. Before discovery of LC, Lehmann designed a microscope that could be used to monitor phase transition process. 1888 by Prof. Reinitzer, a botanist, University of Prague, Germany.

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Chapter 2: Liquid Crystals States between crystalline and isotropic liquid

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  1. Chapter 2: Liquid Crystals States between crystalline and isotropic liquid

  2. Liquid Crystals, 1805-1922. Before discovery of LC, Lehmann designed a microscope that could be used to monitor phase transition process.

  3. 1888 by Prof. Reinitzer, a botanist, University of Prague, Germany

  4. Phase Transition first defined by Georges Freidel in 1922

  5. The ordering parameter S=1/2<3cos2Q-1> S=0, isotropic S=1, Ordered Nematic, S=0.5-0.6

  6. Classification of Smectic Liquid Crystals A type: molecular alignment perpendicular to the surface of the layer, but lack of order within the layer. B type: molecular alignment perpendicular to the surface of the layer, having order within the layer. C type: having a tilted angle between molecular alignment and the surface of the layer.

  7. Smectic B Liquid Crystals

  8. Smectic C Liquid Crystals

  9. Smectic A Liquid Crystals

  10. More Detailed Classification of Smectic Phases

  11. Nematic Liquid Crystals

  12. Cholesteric Phase Liquid Crystals

  13. Polymeric Liquid Crystal

  14. Advantages of Nematic Phase and Cholesteric Phase LC For Display Propose Low Viscosity Fast Response Time

  15. Discotic Liquid Crystals

  16. Response to Electric and Magnetic Fields

  17. External Electric Field and Dielectric Properties of LC molecules

  18. Dielectric Constant ke0L = C = q/V

  19. Flow of ions in the presence of electric field Internal Field StrengthE = E0 – E’

  20. Alignment of LC molecules in Electric Field S = 0 1 > S > 0

  21. m m Dielectric Anisotropy and Permanent Dipole Moment

  22. Dielectric Anisotropy and Induced Dipole Moment

  23. Examples

  24. Magnetic Susceptibility and Anisotropy

  25. Light as Electromagnetic Wave Plane Polarized light can be resolved into Ex and Ey

  26. Birefringence

  27. Ordinary light travels in the crystal with the same speed v in all direction. The refractive index n0=c/v in all direction are identical. Extraordinary lighttravels in the crystal with a speed v that varies with direction. The refractive index n0=c/v also varies with different direction

  28. Generation of polarized light by crystal birefringence

  29. Interaction of Electromagnetic Wave with LC Molecules

  30. Circular Birefringence

  31. Reflection of Circular Polarized Light

  32. Devices for Liquid Crystal Display

  33. Designs of LC cell Electronic Drive AM: active matrix; TFT: thin film transistor; MIM: metal-insulator-metal

  34. Alignment of LC molecules in a Display Device

  35. Dynamic Scattering Mode LCD Device

  36. Twisted Nematic (TN) Device 1971 by Schadt

  37. Optical Response of a Twisted Nematic (TN) Device Applied voltages and optical response

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