Unit 1.2 (intro to liquid crystals)
- 1. Introduction to Liquid Crystals States of Matter What is Liquid Crystal? Classification
- 2. Isotropic vs. Anisotropic Liquids and gases (uniform properties in all directions). Liquid Crystals have orientational order
- 3. Classifications • Lyotropic, Polymeric, and Thermotropic Liquid Crystals • Nematic, cholesteric, smectic, and ferroelectric. • Small molecular, polymer
- 4. 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’.
- 6. 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.
- 7. 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
- 8. Thermotropic Liquid Crystals • Most widely used and extensively studied Liquid Crystals • There are 3 basic phases : Nematics, Cholesterics, and Smectics
- 9. Liquid Crystal Phases Nematic, Smectic & Cholesteric Anisotrpic substances may go through one or several Liquid Crystal Phases
- 12. 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.
Editor's Notes
- #6: N-(4- Methoxybenzylidene)-4-butylaniline (MBBA) molecule N-(4- Methoxybenzylidene)-4-butylaniline (MBBA) molecule