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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

0C 100C

WATER

temperature

CHOLESTERYL MYRISTATE

solid liquid crysta l liquid

71C 85C 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 =

director

q

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Order Parameter

0

0.2

0.4

0.6

0.8

1

O

rderParameter

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 liquid60C 63C 80C 86C

temperature

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Chiral Nematic Liquid Crystal

pitch

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Discotic Liquid Crystals

C8 H17O

C

O

O

C

O

OC8 H17O

O

C

O

O

C

OC8 H17

O

OC8 H17

O

C

O

C8H17O

O

C

O

C8 H17O

temperature

solid columnar nematic

244C

isotropic

152C 168C

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Discotic Phases

nematic columnar

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Lyotropic Liquid Crystals

C

O

O

C15H31

CH3

NCH3CH2

CH3

CH2O P

O

O

OCH2

CH

OC

CH2O

C

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

N

N

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!

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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

IndexofRefraction

Temperature TC

n

n

niso

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LCs between Crossed Polarizers

n

n

n

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

qq

L1

L2

condition for reflection: L2 - L1 = (P/2)(1+cos(q+))/cosq)= n

ifq = and for n = 1, = Pcos q

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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

compensat ion

plat e

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

BR

1R

2

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

protein

phospholipid

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Biology

Cell MembranesOrdered 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 InterestingScientifically

Technologically

Liquid Crystals Are Important

Biology

Chemistry

PhysicsEngineering

Liquid Crystals Are Beautiful!

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