1. Introduction to Liquid Crystals
Chang-Kui Duan
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

2. Chang-Kui Duan, Institute of Modern Physics, CUPT
Contents
0. History of LC and LCD
Fundamentals
Molecular structure and Chemical Composition
Electronic Properties
Lyotropic, Polymeric, and Thermotropic Liquid Crystals
Mixtures and Composites
Liquid Crystal Cells and Sample Preparation
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

3. Liquid Crystal Displays (LCDs) Innovation Timeline
1888, Austrian Botanist Freidrich Reinitzer discovers liquid crystals
1897,German scientist Karl Braun invents the cathode ray tube (CRT)
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

4. Liquid Crystal Displays (LCDs) Innovation Timeline
1958, The first paper research about LCD in the U.S. wrote by Dr. Glenn Brown
1963, Richard Williams and George Heilmeier suggested using liquid crystal materials for display
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

5. Liquid Crystal Displays (LCDs) Innovation Timeline
1967, James Fergason discovered the "twisted nematic" LCD. He produced the first practical displays
1968, RCA group had a display based on the dynamic scattering mode (DSM) of liquid crystals
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

6. Liquid Crystal Displays (LCDs) Innovation Timeline
1972,International Liquid Crystal Company (ILIXCO) produced the first modern LCD watch using Fergason Ideal
1973, ,Sharp produced the first portable calculator, using a DSM LCD screen
1979, Walter Spear and Peter LeComber made the first color display using lightweight thin film transfer (TFT) LCD
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

7. Liquid Crystal Displays (LCDs) Innovation Timeline
1985, Seiko-Epson unveiled the first commercial LCD color TV set, which had a 2 inch view
1992, Sharp developed a multimedia-compatible 16.5 inch color TFT LCD, that was the world's first LCD ViewCam
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

8. Liquid Crystal Displays (LCDs) Innovation Timeline
2000- Present
2004, Philips demonstrated a 20″ 3-D LCD at CeBIT in Hannover
2005, Samsung Developed World's Largest (82") Full HDTV TFT-LCD
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

9. Other LCD application: LCD Projector
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Chang-Kui Duan, Institute of Modern Physics, CUPT

10. Digital Light Processing™ (DLP) Projector
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Chang-Kui Duan, Institute of Modern Physics, CUPT

11. Chang-Kui Duan, Institute of Modern Physics, CUPT
Fundamentals
States of Matter
What is Liquid Crystal?
Classification
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

12. Chang-Kui Duan, Institute of Modern Physics, CUPT
States of Matter
Solid
Liquid crystal
“fourth state of matter”
Liquid
Gas
Images: MacDonald, R. “Liquid Crystals - Fascinating State of Matter or "Soft is beautiful". Accessed
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

13. What is a Liquid Crystal?
Liquid Crystal – a stable phase of matter characterized by anisotropic properties without the existence of a 3-dimensional crystal lattice – generally lying between the solid and isotropic (“liquid”) phase.
Discuss
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

14. Isotropic vs. Anisotropic Liquids and gases
(uniform properties in all directions).
vs. Anisotropic
Do not follow patterns, Some phases are combined and orientation is NOT the only way to characterize
Liquid Crystals
have orientational order
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

15. Chang-Kui Duan, Institute of Modern Physics, CUPT
Liquid Crystal Model
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

16. Chang-Kui Duan, Institute of Modern Physics, CUPT
Classifications
Lyotropic, Polymeric, and Thermotropic Liquid Crystals
Nematic, cholesteric, smectic, and ferroelectric.
Small molecular, polymer
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

17. 2. Molecular structure and Chemical Composition
A side chain R, two or more aromatic rings A and A’, connected by linkage groups X and Y, and at the other end connected to a terminal group R’.
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

18. Chang-Kui Duan, Institute of Modern Physics, CUPT
Examples
N-(4- Methoxybenzylidene)-4-butylaniline (MBBA) molecule
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

19. Chang-Kui Duan, Institute of Modern Physics, CUPT
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

20. Chang-Kui Duan, Institute of Modern Physics, CUPT
Consequence
All the physical and optical properties of liquid crystals are governed by the properties of these constituent groups and how they are chemically synthesized together: Dielectric constants, elastic constants, viscosities, absorption spectra, transition temperatures, existence of mesophases, anisotropies, and optical nonlinearities
Molecules are quite large and anisotropic, practically impossible to treat all the possible variations in the molecular architecture and the resulting changes in the physical properties.
Some generally applicable observations on the dependence of the physical properties on the molecular constituents.
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

21. Chang-Kui Duan, Institute of Modern Physics, CUPT
Chemical stability
Depends on the central linkage group
Schiff-base unstable
Ester, azo, and azoxy stable, but are also quite susceptible to moisture, temperature change, and ultraviolet (UV) radiation.
Compounds without a central linkage group are among the most stable liquid crystals ever synthesized.
Other compounds such as pyrimide and phenylcyclohexane are also quite stable.
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

22. 3. Electronic Properties
Decided by they constituent molecules
Energy level structures rather complex
Theories are still not sufficiently precise in relating the molecular structures and the liquid crystal responses.
Limit here to stating some of the well-established results, mainly from molecular theory and experimental observations.
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

23. energy levels or orbitals of aromatic rings
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

24. Chang-Kui Duan, Institute of Modern Physics, CUPT
Characteristic
Very Absorptive in UV ( < ~ 200 nm)
Quite transparent in Vis and IR (0.4-5 m)
Far IR (>=9 m), very absorptive due to rovibrational transitions
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

25. 4. Lyotropic, Polymeric, and Thermotropic Liquid Crystals
Lyotropic Liquid Crystals are obtained when an appropriate concentration of a material is dissolved in some solvent; Ex: Soap; Are of interest in biological studies.
Polymeric Liquid Crystals are basically the polymer versions of the monomers
Refer to the and 1.3.2
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

26. Thermotropic Liquid Crystals
Most widely used and extensively studied Liquid Crystals
There are 3 basic phases : Nematics, Cholesterics, and Smectics
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

27. Liquid Crystal Phases Nematic, Smectic & Cholesteric
Anisotrpic substances may go through one or several Liquid Crystal Phases
Do not follow patterns, Some phases are combined and orientation is NOT the only way to characterize
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

28. Nematic and Cholesteric
Namatic Cholesteric
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Chang-Kui Duan, Institute of Modern Physics, CUPT

29. Smectic-A and Smectic-C
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Chang-Kui Duan, Institute of Modern Physics, CUPT

30. Smectic C* (ferroelectric) and unwounded Smectic C*
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Chang-Kui Duan, Institute of Modern Physics, CUPT

31. 4. Mixtures and Composites
temperature ranges for pure liquid crystals are quite limited.
Industrial applications employ mostly mixtures, composites, or doped liquid crystals with tailor-made physical and optical properties.
The optical properties, dielectric anisotropies, and viscosities are very different from those of the individual mixture constituents.
Creating mixtures is an art, guided of course by some scientific principles.
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

32. Chang-Kui Duan, Institute of Modern Physics, CUPT
Mixtures
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

33. Dye-Doped Liquid Crystals
Modification of their well-known linear, and more recently observed nonlinear, optical properties
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

34. Polymer-Dispersed Liquid Crystals
See textbook 1.4.3
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

35. 5. Liquid Crystal Cells and Sample Preparation
The alignment of the liquid crystal axis in cells is essentially controlled by the cell walls, whose surfaces are treated in a variety of ways to achieve various director axis alignments.
Bulk Thin Film
Liquid Crystal Optical Slab Waveguide, Fiber, and Nanostructured Photonic Crystals
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

36. Chang-Kui Duan, Institute of Modern Physics, CUPT
Bulk Thin Film
For procedure to prepare, see 1.5.1
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

37. Chang-Kui Duan, Institute of Modern Physics, CUPT
Liquid Crystal Optical Slab Waveguide, Fiber, and Nanostructured Photonic Crystals
1.5.2 for details
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT

38. Order Parameter, Phase Transition,and Free Energies
The contents of next chapter!
2018/1/25
Chang-Kui Duan, Institute of Modern Physics, CUPT