the science and technology of liquid crystals peter j. collings department of physics &...
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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
solid liquid gas
0°C 100°C
WATER
temperature
CHOLESTERYL MYRISTATE
solid liquid crystal liquid
71°C 85°C temperature
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Liquid Crystals
L = 300 J/gm L = 30 J/gm
solid liquid crystal liquid
temperature
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Orientational Order
Order Parameter
S = <(3cos2 - 1)/2>
director
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Order Parameter
0
0.2
0.4
0.6
0.8
1
Order Parameter
TemperatureT
C
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Smectic Liquid Crystals
smectic A
smectic C
director
director
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Typical Liquid Crystal Molecule
C10H21O C
S
O
C5H11
solid smectic C smectic A nematic liquid
60°C 63°C 80°C 86°Ctemperature
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Chiral Nematic Liquid Crystal
pitch
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Discotic Liquid Crystals
C8H17O
CO
O
C
O
OC8H17O
O
C
O
OC
OC8H17
O
OC8H17
O
CO
C8H17O
OC
O
C8H17O
temperature
solid columnar nematic
244°C
isotropic
152°C 168°C
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Discotic Phases
nematic columnar
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Lyotropic Liquid Crystals
CO
O
C15H31
CH3
NCH3 CH2
CH3
CH2O P
O
O
OCH2
CHO CCH2
OC
C
O
C15H31
O
C15H31
+
Na
soap
+ _
phospholipid
_
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Lyotropic Phases
Micelle (cross-section)
Vesicle (cross-section)
water
water
water
water
water
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Liquid Crystal Phases of Aggregates
NN
SO3Na
OH
NaSO3
Sunset Yellow FCF Aggregate
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Nematic Phase of Sunset Yellow
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Viscosity
fixed plate fixed plate fixed plate
moving plate moving plate moving plate
low viscosity low viscosity high viscosity
anisotropy!Return to "Recent Talks" Page
Polarization
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Ez Pz
+-+-
+-+- +-
+-
+- +-+-+
-
Ey
Py
Pz > Py anisotropy
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Birefringence
director
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Birefringence (continued)
1.5
1.6
1.7
Index of Refraction
Temperature TC
n
n
niso
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LCs between Crossed Polarizers
n
nn
dark dark light
polarizer
analyzer
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
P/2
φ L1
L2
condition for reflection: L2 - L1 = (P/2)(1+cos(+))/cos)= n
if = and for n = 1, = Pcos
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Temperature Sensors
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Liquid Crystal Display
liquid crystal
glass
glass
ITOalignmentlayer
polarizing film reflector
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Twisted Nematic LCD
OFF ON
polarizers reflector
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Electrically Controlled Birefringence
polarizers reflector
OFF ON
Top View
compensationplate
Top View
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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
diffuse state (V = 0) clear state (V ≠ 0)
isotropic polymer
liquid crystal droplets
n
n n
n
nP
nP
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Switchable Windows
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Liquid Crystal Droplets
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Biological Sensors
Array of Antibodies in a Chromonic Liquid Crystal
Crossed Polarizers
Immune Complexes
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Synthesis of Liquid Crystals
L1 L2
C1 C2
X1
X2
BR1 R2
C - Core group (benzene, cyclohexane, pyrimidine rings)B - Bridging group (phenyl-, azo-, ester, Schiff’s 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
protein
phospholipid
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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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