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

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

Liquid Crystal Displays (LCDs) Innovation Timeline 1888-1899 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

Liquid Crystal Displays (LCDs) Innovation Timeline 1900-1970 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

Liquid Crystal Displays (LCDs) Innovation Timeline 1900-1970 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

Liquid Crystal Displays (LCDs) Innovation Timeline 1970-1980 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

Liquid Crystal Displays (LCDs) Innovation Timeline 1980- 2000 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

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

Other LCD application: LCD Projector 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

Digital Light Processing™ (DLP) Projector 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

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

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 7-2006 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

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

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

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

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

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

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

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

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

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

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

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

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

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 1.3.1 and 1.3.2 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

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

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

Nematic and Cholesteric Namatic Cholesteric 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

Smectic-A and Smectic-C 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

Smectic C* (ferroelectric) and unwounded Smectic C* 2018/1/25 Chang-Kui Duan, Institute of Modern Physics, CUPT

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

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

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

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

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

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

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

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