The Liquid Crystalline

State of Matter:

From the Laboratory…

to the Shopping Mall

Paul M. GoldbartDepartment of Physics,

Seitz Materials Research Laboratory,

& Institute for Condensed Matter Theory,

University of Illinois at Urbana-Champaign

What I hope you’ll see today…

Applications of liquid crystallinematerials are becoming more and more important in the world around us

A rudimentary understanding of what they are can help us see how and why they are so useful

Billion dollar industries can lie “just around the corner” from the fundamental research laboratory

Plan of action…

Some applications of liquid crystals (or how are they useful)

What actually are liquid crystals?

What basic properties do they have?(or why are they useful?)

What science goes into the key element of a display?

Two (of many) usefulresources…

Peter J. Collings: LiquidCrystals -- Nature’sDelicate Phase of Matter

Oxford Liquid Crystal Technology Group

Lessons From Superconductivity

Steven Weinberg

Nobel Laureate (Physics), 1979 Department of Physics, University of Texas at Austin

October 11, 2007Tuesday, 7:30 p.m.

Ballroom, Campbell Alumni Center601 South Lincoln Street, Urbana

Symmetry is a fundamental organizational principle of nature. Patterns of symmetry

breaking define disparate phases of matter. This talk will highlight the common thread

between broken symmetry in superconductivity and the origin of

mass in particle physics.

Once upon a time…

I had to motivate this talk with examples that weren’t familiar…

Once upon a time…

I had to motivate this talk with examples that weren’t familiar…

But not any more…

But not any more…

But not any more…

•colour

•many picture elements (picsels)

pocket calculators

wristwatches car displays computer

screens thin televisions …

•cell appears silvery, mirror-like

•how do we change its appearanceso that we can write (and change) information on it?

Atoms or molecules…• form a regular array

• jiggling randomly

• a crystal

• a rigid structure

• condense but roam randomly

• not rigid

• flows when poured

• explore container

• roam randomly

What are liquid crystals?

First: the traditional states of

matter

So far, we have seen things

that are not liquid

crystals…

Liquid crystals are

states of matter

having…

Focus on time-averagedorientation insome littlevolume

Simplest example of

the liquid crystalline state…

How do uniaxial nematics

respond to distortion?

(molecules aligned, on average, along dark lines)

Liquid crystalline states: Some more intricate examples

Many moreexamples: Sm A-K,…

Ex: cholesteryl myristate “cholesterics”

Yet another example…

Freedericksz effect: competition between alignment

bythe electric field and by the

boundary

Ingredients for a liquid crystal display ― but first… how does light pass through liquid crystalline media?

(a)polarisation parallel to molecules,so one speed only,

so vert pol → vert pol → extinction

(b) polarisation not parallel to molecules,so para & perp components travel at distinct speeds,so vert polarisation → elliptical polarisation (E rotating)

→ some transmission

• after polarisation: all colours are vertically linearly polarised

• vert lin pol = L & R circularly polarisation

• L & R travel at distinct speeds in this chiral medium(call this: circular birefringence)

• how distinct? depends on the colour (of the light)

• at analyser: L & R remake linearly polarised light,but it’s no longer vertically polarised

• one colour is now horizontally polarised, that colour is preferentially transmitted

• Blue light has been preferentially transmitted

• boundaries chosen to anchor molecule orientation(& induce twist)

• choose material with slight intrinsic chirality (e.g. additive)

• no voltage between electrodes → no electric field

• twist → circular birefringnce (L & R pol’s travel at distinct speeds) → plane of polarisation rotated to that of polarizer II

• choose cell thickness & liquid crystal material to get 90º rotation at polariser II → transmission at

polariser II

• reflection at mirror, unrotation, emergence at polariser I

• boundaries still anchor molecular orientation

• but light now travels mostly roughly parallel to molecules

• much less than 90º rotation at polariser II

• much less light is reflected & emerges

And now you can make…

So, I hope you’ve seen that…

Applications of liquid crystallinematerials are becoming more and more important in the world around us

A rudimentary understanding of what they are can help us see how and why they are so useful

Billion dollar industries can lie just around the corner from the fundamental research laboratoryThanks for your attention!

A few resources…

Liquid Crystals ― Nature’sDelicate Phase of Matterby P.J. Collings

The Physics of Liquid Crystalsby P-G. de Gennes and J. Prost

Introduction to Liquid Crystalsby E.B. Priestley et al.

Liquid Crystalsby S. Chandrasekhar

Kent State Liquid Crystal Institutehttp://lci.kent.edu

Oxford Liquid Crystal Technology Grouphttp://eng.ox.ac.uk/lc/introduction_1.html