From the theory of liquid crystals to LCD-displays Nobel Price in Physics 1991: Pierre-Gilles de Gennes Alexander Kleinsorge FHI 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: W 1 -C 6 H 4 -M-C 6 H 4 -W 2 (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 smectic disordered +orientated +positioned
Degrees of Freedom Chirality in LCs: different d.o.f. melt at different phasetransition-temperatures LCs: position (3) + orientation (3) similar: Curietemperature 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 / Distomers 2001, Hazen+Filley: separation of aminoacids at calzit
LC-Examples cigar shaped: discotic: banana:
Director Orientation director orientation minimizes the free energy total Energy: E T = E elast +E electric +E interface E elast = E interface = E electric =
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=c 0 /c m 1, birefringence occurs with: n( k/ k ) B E x normal case birefringence Phase difference results in changed polarization ellipse! Polarizer as filter, 2 perpendicular P. block all light!
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 in helical state, LC is sequence of polarizers cos n (90 /n), n>>100 Waveguiding
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 Twisted 90 light plane rotation / 270 l.p.r. - Voltage: V ST < V T <V! - AC to avoid electrochemical processes Gooch-Tarry-Curve T(retardation)
Color Pixel polarizer glass-substrate ITO-layer liquid crystal ITO-layer glass-substrate polarizer unpolarized white light TFT (later) orientation layer orientation layer color-filter R G B
Display Types pure LCD (black/white, pocket calculator,clocks) reflective ambient light, 2x turning DSTN, passive matrix display, column row grid (old laptops) t.l. s.s. TFT, Thin Film Transistor, active matrix display (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 Displays mostly 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