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

Outline  Introduction to Liquid Crystals  Mechanical, Electrical, and Optical Properties  Liquid Crystal Display Technology  Chemistry of Liquid Crystals  Biology of Liquid Crystals Return to "Recent Talks" Page

Phases of Matter solid 0°C WATER liquid 100°C gas temperature CHOLESTERYL MYRISTATE solid 71°C liquid crystal liquid 85°C temperature Return to "Recent Talks" Page

Liquid Crystals solid liquid crystal L = 300 J/gm liquid temperature L = 30 J/gm Return to "Recent Talks" Page

director Orientational Order Order Parameter S = <(3cos 2 q - 1)/2> q Return to "Recent Talks" Page

Order Parameter 1 0.8

0.6

0.4

0.2

0 Temperature T C Return to "Recent Talks" Page

Smectic Liquid Crystals director smectic A director smectic C Return to "Recent Talks" Page

Typical Liquid Crystal Molecule C 10 H 21 O C O S C 5 H 11 solid 60°C smectic C 63°C smectic A 80°C nematic 86°C liquid temperature Return to "Recent Talks" Page

Chiral Nematic Liquid Crystal pitch Return to "Recent Talks" Page

Discotic Liquid Crystals C 8 H 17 O C 8 H 17 O C O O O C O O C O O C O OC 8 H 1 7 C 8 H 17 O O C O O O C OC 8 H 1 7 solid 152°C columnar 168°C OC 8 H 1 7 nematic 244°C isotropic temperature Return to "Recent Talks" Page

Discotic Phases nematic columnar Return to "Recent Talks" Page

Lyotropic Liquid Crystals + Na _ O C O C 15 H 31 soap CH 3 + CH 3 N CH 2 CH 2 O CH 3 _ O P O O O CH 2 CH CH 2 C O O C C O C 15 H 31 C 15 H 31 phospholipid Return to "Recent Talks" Page

Lyotropic Phases water water water water Micelle (cross-section) water Vesicle (cross-section) Return to "Recent Talks" Page

Liquid Crystal Phases of Aggregates

Aggregate

NaSO 3

Sunset Yellow FCF

OH N N SO 3 Na Return to "Recent Talks" Page

Nematic Phase of Sunset Yellow Return to "Recent Talks" Page

Viscosity moving plate fixed plate low viscosity moving plate moving plate fixed plate fixed plate low viscosity high viscosity anisotropy!

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E

z

P

z + + + + + + + + + -

P

z

> P

y Polarization + + + + + + +

P

y + +

E

y

anisotropy

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Birefringence

director

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Birefringence (continued) 1.7

n 1.6

n 1.5

n iso Temperature T C Return to "Recent Talks" Page

n

LCs between Crossed Polarizers polarizer analyzer

n n

E

dark dark light

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Nematic Liquid Crystal Return to "Recent Talks" Page

Smectic Liquid Crystal Return to "Recent Talks" Page

Chiral Nematic Liquid Crystal Return to "Recent Talks" Page

Selective Reflection  q  P/2 q L 1 L 2 condition for reflection: L 2 - L 1 = (P/2)(1+cos( q +  ))/cos q )= n  if q =  and for n = 1,  = Pcos q Return to "Recent Talks" Page

Temperature Sensors Return to "Recent Talks" Page

polarizing film ITO Liquid Crystal Display glass liquid crystal glass reflector alignment layer Return to "Recent Talks" Page

polarizers OFF Twisted Nematic LCD ON reflector Return to "Recent Talks" Page

Electrically Controlled Birefringence

OFF ON

polarizers ref lect or

Top View

compensat ion plat e

Top View

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Computer Monitor Return to "Recent Talks" Page

Small Displays Return to "Recent Talks" Page

Light Shutters Return to "Recent Talks" Page

PDLC Windows & Displays isotropic polymer n n P n n n P

diffuse state (V = 0) clear state (V ° 0)

liquid crystal droplets n Return to "Recent Talks" Page

Switchable Windows Return to "Recent Talks" Page

Liquid Crystal Droplets Return to "Recent Talks" Page

Biological Sensors Crossed Polarizers Immune Complexes Array of Antibodies in a Chromonic Liquid Crystal Return to "Recent Talks" Page

Synthesis of Liquid Crystals X 1 B R 1 C 1 C 2 R 2 L 1 L 2 X 2 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, -NO 2 ) X - Lateral group (-H, -F, -Cl, -Br, -NO 2 ) Return to "Recent Talks" Page

Double Twist Cylinders Return to "Recent Talks" Page

Simple Cubic Structure Return to "Recent Talks" Page

Blue Phase Single Crystals Return to "Recent Talks" Page

phospholipid Phospholipid Bilayers protein Return to "Recent Talks" Page

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 Return to "Recent Talks" Page

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?) Return to "Recent Talks" Page

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

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