From the theory of liquid crystals - The NOMAD...
Transcript of From the theory of liquid crystals - The NOMAD...
From the theoryof liquid crystalsto LCD-displays
Nobel Price in Physics 1991: Pierre-Gilles de Gennes
Alexander KleinsorgeFHI Berlin, Dec. 7th 2004
Outline
• Survey of Liquid Crystals• Anisotropy properties• LC Displays• Other Applications
Complex Fluids
• broken symmetry, e.g. liquid crystals• slowly relaxing degrees of freedom:
e.g. polymers• heterogeneous sytems, e.g. colloids
(varnish,spumes,milk) – surface effects • modifiable basic modules, e.g.
miscellanea (red blood cells)
Liquid Crystals• state of matter between liquid and solid
( not isotropic, but liquid )• discovered by Friedrich Reinitzer in 1888
( first sample was cholesteryl benzonate )• 13000 mostly organic molecules are known• bacillary: W1-C6H4-M-C6H4-W2 (W..wing,M..middle)
Smectic A Mesophase (l)
and
Columnar Phase (r)
Types of Liquid Crystals (LC)• lyotropic LC: soap, biological membranes• thermotropic LC: LC-Phase exists in a range of
temperature between clarification and melting– sub-classification: nematic(normal,
cholesterolic,columnar-nematic), smectic (A..I), columnar(oblique angle,right a.,hexagonal)
• banana-phase becomes obsolete
isotropic nematic smecticdisordered +orientated +positioned
Degrees of Freedom Chirality
• in LCs: different d.o.f. melt at different phase-transition-temperatures
• LCs: position (3) + orientation (3)
• similar: Curie-temperature for spins
• chiral: molecules that aren’t its reflection
• asymmetric molecules with asymmetric C-atoms
• 2 enantiomorphs:distomer and eutomer
• racemic ( 1:1 mixture )
distomer - eutomer
Aminoacids in Life are counterclockwise
Chirality:
Eutomers / Distomers2001, Hazen+Filley: separation of aminoacids at calzit
LC-Examples
• cigar shaped:
• discotic:
• banana:
Director Orientation• director orientation minimizes the free energy• total Energy: ET= Eelast+Eelectric+Einterface
Eelast=
Einterface=
Eelectric=
Electric Anisotropy: ε• an example of anisotropic parameter is
the dielectric constant ε ; susceptibility• positive a.: along the molecule ε is larger
tend to align parallel to the E-field • negative anisotropy: mostly discotic
shaped molecules
switchable medium (applied voltage)
Light Wave - Photon• Maxwell Eq: E┴B┴k• n=c0/cm≥1, birefringence
occurs with: n( k/ ||k|| )
xB
E
Polarizer as filter, 2 per-pendicular P. block all light !Phase difference results in
changed polarization ellipse !
normal case
birefringence
Birefringence ∆n≠0• anisotropic refractive index n
rotation of polarization plane from light• happens with chiral molecules
(chiral: molecules that aren’t its reflection *)e.g. polysaccharides, liquid crystals, lactic acid, contergan, ..
• natural light is non-polarized (Boltzmann radiation)• polarizer only let pass one polarization (50%)
Waveguiding• waveguiding in
helical state,LC is sequenceof polarizers
cosn(90°/n), n>>100
Twisted Nematic LCD (TN-LCD)• multi layer: polarizer/analyzer, glass,
ITO capacitor, alignment layer (rubbing)• Normally White Mode• waveguiding• glass-balls used
as µm-spacer
• LCD mostly nematic
Twisted vs. Super Twisted90° light plane rotation / 270° l.p.r.
Gooch-Tarry-CurveT(retardation)
- Voltage: ∆VST< ∆VT<V !- AC to avoid electro-chemical processes
Color Pixel
R G B
unpolarized
white light
TFT (later)
orientation layer
orientation layer
color-filter
polarizer
glass-substrate
ITO-layer
liquid crystal
ITO-layer
glass-substrate
polarizer
Display Types• pure LCD (black/white, pocket calcu-
lator,clocks) – reflective ambient light, 2x turning
• DSTN, passive matrix display, column row grid (old laptops) – t.l. s.s.
• TFT, Thin Film Transistor, active matrixdisplay (Laptops >13“) – t.l. s.s.
• OLED, organic LED - matrix of self luminous pixels
• under develop.: SSFLC, ferroelectr. LCD(µs not ms),PDLC, polymer-dispersed LCDs
*t.l. s.s. = transmission light, separate source
Other Applications of LC, but Displaysmostly viscosity f(order)
• tearproof fibers (Kevlar, better than steel)• wearless brakes (>100x /sec)• thermography (optical, area)• adjustable damping• high-power
laser focusing
Nobel Prizes for Displays• Physics 1991:
Gennes; ( only 5+2 pages nobel lecture )
ordering of LC• Chemistry 2000:
Heeger, MacDiarmid, Shirakawa; conductive polymers (OLED)
• Chemistry 2001:Sharpless, Knowles, Noyori;chirally catalysis (LCD)
www.nobel.se
LC-Videos
Collapse Oscilation
http://liq-xtal.cwru.edu/Videos.htm
Notes• LCD $15b annual industry world-wide• References:
- http://www.elis.ugent.be/ELISgroups/lcd/lc/lc.html- http://www.presse-highlights.merck.de/
servlet/PB/show/1132890/Aktiv-Matrix_deutsch.pdf- http://www.mpip-mainz.mpg.de/~pleiner/papers/mkfa2.pdf- http://www.kth.se/fakulteter/tfy/kmf/lcd/lcd~1.htm- „Fachlexikon ABC Chemie", Ed.: Hans-Dieter Jakubke and
Hans Jeschkeit, Frankfurt am Main 1987, Band 1, p. 399-402