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Liquid Crystal and
Liquid Crystal Polymers
By,
Saurav Chandra Sarma
Int. Ph.D. 4th Sem.
Liquid Crystal and Life
Liquid crystals are also fundamentally
important to life. DNA and cell
membranes have liquid cryst...
 Liquid crystals (LCs) are matter in a state that has properties between
those of conventional liquid and those of solid ...
Positional Order + Orientational Order = Crystal Phase
Positional Order + No Orientational Order = Plastic Phase
Varying P...
Liquid Crystal-Is it a Solid or Liquid..???
 The amount of energy required to cause the phase transition is called latent...
Mesophase: a phase lying between solid (crystal)
and isotropic (liquid) states.
Liquid crystals: fluid (l) but also show b...
Liquid Crystals
Thermotropic Lyotropic
High molecular
(molar) mass
[ polymers]
Low molecular
(molar) mass
Main-chain
polym...
No translational order—Nematics
 The word “Nematic" is derived from the
Greek word for thread-like structure.
 It is the...
One-dimensional translational order—Smectic
 The word "Smectic" is derived from the Greek word for soap
 Liquid-like mot...
Chiral Liquid Crystal- Cholesteric
 Also known as “Chiral nematic”
 Molecules have non-symmetrical carbon
atoms and thus...
Lyotropic Liquid Crystal
 Lyotropic LCs are two-component systems where an amphiphile is dissolved in a
solvent.
 Lyotro...
Thermotropic Liquid Crystal
 The transitions to the liquid crystalline state are induced thermally
Thermotropic Liquid Crystal
 The essential requirement for a molecule to be a thermotropic LC is a structure
consisting o...
Order Parameter
 To quantify just how much order is present in a
material, an order parameter (S) is defined.
 Theta is ...
External influences on Liquid Crystals
External perturbation can cause significant changes in the macroscopic properties o...
Birefringence in Liquid Crystals
When light enters a birefringent material, such as a nematic liquid crystal
sample, the p...
Liquid Crystal Textures
The term texture refers to the orientation of liquid crystal molecules in the vicinity
of a surfac...
Defects Under the Microscope:
• The abrupt changes in brightness seen in the pictures signal a rapid change in
director or...
Calamitic vs. Discotic Nematics
Experimental Identification of Liquid
Crystals
 Differential Scanning Calorimetry (DSC): It
provides valuable information...
Experimental Identification of Liquid
Crystals
 X-ray Crystallography: This can be used to study the extent of
translatio...
Applications of liquid crystals
 Display application of liquid
crystals: The most common
application of liquid crystal
te...
Characteristics:
• These are a class of aromatic polymer.
• Extremely unreactive and inert.
• Highly resistant to fire.
Li...
Polymer Liquid Crystals
Advantage of Liquid Crystal Polymer (LCP)
Advantage of LCP
 High heat resistance
 Flame retardant
 Chemical resistance
 Dimensional stability
 Mold ability
 H...
• Soap
• Conducting foams
• Heat Sensitive cameras use liquid crystal screens
that respond to heat.
Applications
• Kevlar, the most widely used body armor is made up of
intertwined liquid crystal polymers.
Applications
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Liquid Crystal and Liquid Crystal Polymer

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Liquid Crystal polymer,types and its applications

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Liquid Crystal and Liquid Crystal Polymer

  1. 1. Liquid Crystal and Liquid Crystal Polymers By, Saurav Chandra Sarma Int. Ph.D. 4th Sem.
  2. 2. Liquid Crystal and Life Liquid crystals are also fundamentally important to life. DNA and cell membranes have liquid crystal phases. Our brains are around 70% liquid crystal, and liquid crystals are also found in muscles, the amazing iridescent colours of some insects, and also slug slime! Liquid crystals are beautiful and mysterious; I am fond of them for both reasons. - P.G. De Gennes
  3. 3.  Liquid crystals (LCs) are matter in a state that has properties between those of conventional liquid and those of solid crystal.  For instance, an LC’s may flow like a liquid, but its molecules may be oriented in a crystal like way.  There are many different type of LC phases, which can be distinguish by their different “optical properties” (such as birefringence. Which viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures. Introduction
  4. 4. Positional Order + Orientational Order = Crystal Phase Positional Order + No Orientational Order = Plastic Phase Varying Positional Order + Orientational Order = Liquid Crystal Phase No Positional Order + No Orientational Order = Isotropic Phase Liquid crystals are classified in terms of following criterion: (1) Translational order/ Positional Order (2) Bond orientational order (3) Correlation between smectic layers (4) With chirality? (5) Cubic structure?
  5. 5. Liquid Crystal-Is it a Solid or Liquid..???  The amount of energy required to cause the phase transition is called latent heat of the transition and is useful to measure of how different the two phases are.  In the case of cholesteryl myristate, the latent heat of solid to liquid crystal is 65 calories/gram,while the latent heat for liquid crystal to liquid transition is 7 calories/gram.  The smallness the latent heat of liquid crystal to liquid phase transition is evidence that liquid crystal are more similar to liquids than they are to solids.
  6. 6. Mesophase: a phase lying between solid (crystal) and isotropic (liquid) states. Liquid crystals: fluid (l) but also show birefringence (c); have properties associated with both crystals and liquids. Thermotropic: liquid crystalline phase is formed when the pure compound is heated. Lyotropic: liquid crystalline phase forms when the molecules are mixed with a solvent (solution). Liquid Crystalline Phases
  7. 7. Liquid Crystals Thermotropic Lyotropic High molecular (molar) mass [ polymers] Low molecular (molar) mass Main-chain polymers Side-chain polymers Rod-like or lath-like molecules Calamitic Disc-like molecules Discotic Single or multicomponent systems Homo- or co-polymers Figure 9.1 The liquid crystal family tree.
  8. 8. No translational order—Nematics  The word “Nematic" is derived from the Greek word for thread-like structure.  It is the only liquid crystal phase with no long range translational order.  It is the least ordered mesophase  Preferred Orientation is denoted by the ‘Director’ n.  This phase has a symmetrical axis C∞ along the director  Point Group D∞h.  It has thread like structure when seen under polarizing microsope.
  9. 9. One-dimensional translational order—Smectic  The word "Smectic" is derived from the Greek word for soap  Liquid-like motion of the rods in each layer  No correlation of the molecular positions from one layer to the next  The layers can easily slide  In the smectic A phase, molecules tend to be perpendicular to the smectic layers  In the smectic C phase, the molecules in the layers are parallel and tilted in arrangement with respect to the normal of the layers by a tilt angle θ.
  10. 10. Chiral Liquid Crystal- Cholesteric  Also known as “Chiral nematic”  Molecules have non-symmetrical carbon atoms and thus lose mirror symmetry  Shows a helical structure.  In general the helical pitch of cholesteric liquid crystals is of the order of visible light’s wavelength—about a few hundreds nm and so shows different color.
  11. 11. Lyotropic Liquid Crystal  Lyotropic LCs are two-component systems where an amphiphile is dissolved in a solvent.  Lyotropic mesophases are concentration and solvent dependent.
  12. 12. Thermotropic Liquid Crystal  The transitions to the liquid crystalline state are induced thermally
  13. 13. Thermotropic Liquid Crystal  The essential requirement for a molecule to be a thermotropic LC is a structure consisting of a central rigid core (often aromatic) and a flexible peripheral moiety (generally aliphatic groups). This structural requirement leads to two general classes of LCs: 1. Calamitic LCs: Calamitic or rod-like LCs are those mesomorphic compounds that possess an elongated shape. Divided into 2 groups: Nematic and Smectic 2. Discotic LCs:
  14. 14. Order Parameter  To quantify just how much order is present in a material, an order parameter (S) is defined.  Theta is the angle between the director and the long axis of each molecule  The brackets denote an average over all of the molecules in the sample.  In an isotropic liquid, the average of the cosine terms is zero, and therefore the order parameter is equal to zero.  For a perfect crystal, the order parameter evaluates to one  Typical values for the order parameter of a liquid crystal range between 0.3 and 0.9, with the exact value a function of temperature, as a result of kinetic molecular motion. S=(1/2)<3Cos2q -1> Nematic LC
  15. 15. External influences on Liquid Crystals External perturbation can cause significant changes in the macroscopic properties of the liquid crystal system. The order of liquid crystals can be manipulated by mechanical, electric or magnetic forces.  Electric and Magnetic field effect: Due to the effect of electric field permanent electric dipole results which aligns the director along the electric field. The effect of magnetic field is analogous to the electric field.  Surface Preparations: It is possible, however, to force the director to point in a specific direction by introducing an outside agent to the system. For example, when a thin polymer coating (usually a polyimide) is rubbed in a single direction,on a glass substrate, with a cloth, it is observed that liquid crystal molecules in contact with that surface align with the rubbing direction.
  16. 16. Birefringence in Liquid Crystals When light enters a birefringent material, such as a nematic liquid crystal sample, the process is modeled in terms of the light being broken up into the fast (called the ordinary ray) and slow (called the extraordinary ray) components. Because the two components travel at different velocities, the waves get out of phase. When the rays are recombined as they exit the birefringent material, the polarization state has changed because of this phase difference
  17. 17. Liquid Crystal Textures The term texture refers to the orientation of liquid crystal molecules in the vicinity of a surface. Each liquid crystal mesophase can form its own characteristic textures,which are useful in identification. We consider the nematic textures here. If mesogenic materials are confined between closely spaced plates with rubbed surfaces (as described above) and oriented with rubbing directions parallel, the entire liquid crystal sample can be oriented in a planar texture, as shown in the following diagram
  18. 18. Defects Under the Microscope: • The abrupt changes in brightness seen in the pictures signal a rapid change in director orientation in the vicinity of a line or point singularity known as a disclination. A disclination is a region where the director is undefined. The following is a diagram that shows the orientation of the director around a disclination. Defects in Liquid Crystal
  19. 19. Calamitic vs. Discotic Nematics
  20. 20. Experimental Identification of Liquid Crystals  Differential Scanning Calorimetry (DSC): It provides valuable information like the exact transition temperatures and the enthalpies of the different phases  Polarizing Microscope: When a liquid crystal material is placed on a microscope slide with a cover slip and the slide is heated and viewed using a polarizing microscope, textures characteristic of each type of liquid crystal can be seen.
  21. 21. Experimental Identification of Liquid Crystals  X-ray Crystallography: This can be used to study the extent of translational or positional order, and thus infer the type of liquid crystal phase  Extended X-ray absorption fine structure spectroscopy (EXAFS): EXAFS was used to investigate the local structure of the polar spines of metal ion soaps in the columnar liquid crystalline state
  22. 22. Applications of liquid crystals  Display application of liquid crystals: The most common application of liquid crystal technology is liquid crystal displays (LCDs.)  Thermal mapping and non- destructive testing  Medicinal Uses: Cholesteric liquid crystal mixtures have also been suggested for measuring body skin temperature, to outlines tumours etc.  Optical Imaging and Liquid Crystal Interactions with Nanostructure  Liquid Crystal in Chromatography  Liquid Crystal as Solvents in Spectroscopy
  23. 23. Characteristics: • These are a class of aromatic polymer. • Extremely unreactive and inert. • Highly resistant to fire. Liquid crystallinity in polymers can be obtained :  By dissolving in a solvent. (Thermotropic)  By heating above melting transition point. (Lyotropic) Liquid Crystal Polymer (LCP)
  24. 24. Polymer Liquid Crystals
  25. 25. Advantage of Liquid Crystal Polymer (LCP)
  26. 26. Advantage of LCP  High heat resistance  Flame retardant  Chemical resistance  Dimensional stability  Mold ability  Heat aging resistance  Adhesion  Low viscosity  Wieldable  Low cost Disadvantage of LCP  Form weak weld lines  Highly anisotropic properties  Drying required before processing  High Z-axis thermal expansion coefficient
  27. 27. • Soap • Conducting foams • Heat Sensitive cameras use liquid crystal screens that respond to heat. Applications
  28. 28. • Kevlar, the most widely used body armor is made up of intertwined liquid crystal polymers. Applications

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