The Science and Technology of Liquid Crystals Peter J. Collings Department of Physics & Astronomy Swarthmore College June 21, 2007 Return to "Recent Talks"

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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