The Liquid Crystalline State of Matter: From the Laboratory… to the Shopping Mall Paul M. Goldbart Department 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 crystalline materials 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) useful resources… Peter J. Collings: Liquid Crystals -- Nature’s Delicate 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, 2007 Tuesday, 7:30 p.m. Ballroom, Campbell Alumni Center 601 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…

colour many picture elements (picsels)  pocket calculators  wristwatches  car displays  computer screens  thin televisions  …

cell appears silvery, mirror-like how do we change its appearance so 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-averaged orientation in some little volume 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 more examples: Sm A-K,… Ex: cholesteryl myristate “cholesterics” Yet another example…

Freedericksz effect: competition between alignment by the 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 crystalline materials 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 Thanks for your attention!

A few resources…  Liquid Crystals ― Nature’s Delicate Phase of Matter by P.J. Collings  The Physics of Liquid Crystals by P-G. de Gennes and J. Prost  Introduction to Liquid Crystals by E.B. Priestley et al.  Liquid Crystals by S. Chandrasekhar  Kent State Liquid Crystal Institute  Oxford Liquid Crystal Technology Group