The Science and Technology of Liquid Crystals

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The Science and Technology of Liquid Crystals

• Peter J. Collings
• Department of Physics Astronomy
• Swarthmore College
• June 21, 2007

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Outline

• Introduction to Liquid Crystals
• Mechanical, Electrical, and Optical Properties
• Liquid Crystal Display Technology
• Chemistry of Liquid Crystals
• Biology of Liquid Crystals

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Phases of Matter
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Liquid Crystals
solid
liquid crystal
liquid
L 300 J/gm
L 30 J/gm
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Orientational Order
Order Parameter
S lt(3cos2q - 1)/2gt
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Order Parameter
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Smectic Liquid Crystals
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Typical Liquid Crystal Molecule
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Chiral Nematic Liquid Crystal
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Discotic Liquid Crystals
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Discotic Phases
nematic
columnar
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Lyotropic Liquid Crystals
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Lyotropic Phases
Micelle (cross-section)
Vesicle (cross-section)
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Liquid Crystal Phases of Aggregates
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Nematic Phase of Sunset Yellow
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Viscosity
low viscosity
low viscosity
high viscosity
anisotropy!
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Polarization
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Birefringence
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Birefringence (continued)
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LCs between Crossed Polarizers
E
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Nematic Liquid Crystal
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Smectic Liquid Crystal
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Chiral Nematic Liquid Crystal
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Selective Reflection
l
condition for reflection L2 - L1
(P/2)(1cos(??))/cos?) n? if ? ? and for n
1, ? Pcos ?
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Temperature Sensors
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Liquid Crystal Display
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Twisted Nematic LCD
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Electrically Controlled Birefringence
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Computer Monitor
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Small Displays
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Light Shutters
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PDLC Windows Displays
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Switchable Windows
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Liquid Crystal Droplets
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Biological Sensors
Crossed Polarizers
Immune Complexes
Array of Antibodies in a Chromonic Liquid Crystal
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Synthesis of Liquid Crystals
C - Core group (benzene, cyclohexane,
pyrimidine rings) B - Bridging group (phenyl-,
azo-, ester, Schiffs base) L - Linking group
(oxy-, carboxyl-) R - End group (hydrocarbon,
-CN, -NO2) X - Lateral group (-H, -F, -Cl, -Br,
-NO2)
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Double Twist Cylinders
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Simple Cubic Structure
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Blue Phase Single Crystals
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Phospholipid Bilayers
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Biology

• Cell Membranes
• Ordered substrate (hydrophilic, hydrophobic)
• Role of cholesterol (amount of order)
• Muscle
• Microfilaments (actin, myosin)
• Architecture (chiral nematic?)
• Microtubules (cytoskeleton, spindle fibers)
• DNA packing in chromosomes

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Medicine

• Sickle-Cell Anemia (abnormal hemoglobin
  aggregates?)
• Atherosclerosis (cholesterol esters in liquid
  crystal phase?)
• Anesthetics (environment of membrane proteins?)
• Cancer (order of microfilaments within cell?)

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Conclusions

• Liquid Crystals Are Interesting
• Scientifically
• Technologically
• Liquid Crystals Are Important
• Biology
• Chemistry
• Physics
• Engineering
• Liquid Crystals Are Beautiful!

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