Download to read offline
More Related Content
Liquid crystals
- 1.
- 2. States of Matter LiquidCrystal is a Intermediate Phase in matter Difference in various states lies in the order of matter The order is a function of energy and hence the temperature Different States at different temperature
- 3. What is LiquidCrystal? Misogenic State or Misogen Occurs between the crystalline solid state and the isotropic liquid state at distinct temperature ranges Possess some typical properties of a crystalline elastic solid but also have the characteristic properties of an ordinary viscous liquid
- 4. History of LiquidCrystals Friedrich Reinitzer in 1888 noticed that cholesteryl benzoate Had two melting points. At 145.5 °C it melts into a cloudy liquid till it melts down to clear liquid at 178.5 °C. Otto Lehmann later reported seeing crystalline structure in that cloudy liquid and so he named it liquid crystals in 1904
- 5. Properties of LiquidCrystals • Solid Like Properties: Orderly Arrangements of particles, Anisotropy (Mostly in their optical properties) • Liquid Like Properties: Fluidity, Viscosity, Surface Tension • Cloudy in appearance, which means that they scatter light in much the same way as colloids such as milk • The anisotropy of liquid crystals causes them to exhibit birefringence • Liquid Crystals are subject to thermal expansion
- 6. Types of LiquidCrystals On the Basis of Formation 1. Thermotropic Liquid Crystals Temperature Variant 2. Lyotropic Liquid Crystals Solvent + Temperature Variant
- 7. Thermotropic Liquid Crystals Aliquid crystal is thermotropic if its order of matter is determined by temperature change Obtained by • heating a crystalline solid • cooling an isotropic liquid
- 8. Phases of ThermotropicLC 1.Nematic Phase 2.Smectic Phase 3.Cholestric Phase Based on ordering of molecules there are different type of phases that appear due to temperature changes
- 9. Nematic Phase molecular orientationsare correlated, while molecular positions are not.
- 10. Nematic Phase Threadlike Structurewhich are formally called disclinations Positional Ordering is absent Translational Ordering is present Free to Flow like isotropic liquids Most nematics are uniaxial, The axis is called director Some are biaxial Nematic Phase LC can be easily aligned by an external magnetic or electric field
- 11. Smectic Phase The moleculesare arranged in layers and exhibit some correlations in their positions in addition to the orientational ordering.
- 12. Smectic Phase Positionaly Orderedin one direction Layer structure, One Slides over another like in Soap found at lower temperatures than the nematic Unaffected by Magnetic Field
- 13. Types of SmecticPhases Depending on the molecular order in layers, a number of different types of smectics have been observed • Smectic A • Smectic B • Smectic C
- 14. Smectic A Molecules arealigned perpendicular to the layers, without long-range crystalline ordering within them
- 15. Smectic B There isa hexagonal crystalline order within the layers Most ordered among A, B and C
- 16. Smectic C The preferredmolecular axis is not perpendicular to the layers, so that the phase has biaxial symmetry
- 17. Cholesteric Phase This phaseexhibits a twisting of the molecules perpendicular to the director, with the molecular axis parallel to the director
- 18. Cholesetric Phase • CholestericPhase exhibits chirality • Long Range Orientational Order but no long range Positional order • The director varies throughout the medium in a regular way even in an unstrained state • Only chiral molecules can give rise to such a phase
- 19. Cholesteric Phase • Thechiral pitch, p, refers to the distance over which the LC molecules undergo a full 360° twist • The structure repeats itself every half-pitch • The pitch, p, typically changes when the temperature is altered or when other molecules are added to the LC
- 20. Lyotropic Liquid Crystals •For lyotropic liquid crystals the important controllable parameter is the concentration, rather than temperature or pressure • Formed by dissolving an amphiphilic mesogen in a suitable solvent • Amphiphilic Molecule = Hydrophilic + Hydrophobic
- 21.
- 22. Liquid Crystal Displays(LCD) LCDis a flat electronic display panel used for visual aid. It uses Liquid Crystals to create visual effects on screen Important Notes for building LCD • The Intensity of the light can be controlled at any given point by changing the orientation of molecules in Crystal Structure • The orientation of molecules in LC can be manipulated by changing the electric field and magnetic field • There are transparent materials that can conduct electricity
- 23.
- 24. Liquid Crystal Thermometer Aliquid crystal thermometer, temperature strip or plastic strip thermometer is a type of thermometer that contains heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to indicate different temperatures Temperature changes can affect the colour of a liquid crystal, which makes them useful for temperature measurement • They can be used to observe that heat flows by conduction, convection, and radiation • In medical applications they may be used to read body temperature by placing them against the forehead
- 25. Charge Indicator forbatteries The principle is similar to LC thermometers Electrical current passing through the media generates heat. Heat changes temperature which in turn relative orientation of molecules in the LC. Change in orientation causes the change in color which is calibrated to different levels of charge in battery.
- 26. Conclusion Examples of liquidcrystals can be found both in the natural world and in technological applications Though liquid crystals are mostly known for their application in flat panel displays. their unique properties have been used in a number of other applications, such as organic electronics nanoparticle organization and liquid crystal colloids liquid crystal elastomer actuators, as well as chemical and biological sensors Though it was discovered over a century ago the works in LC are still at its peak and there will be more to see in Future