From the theory of liquid crystals to LCD-displays

Transcription

1 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

2 Outline Survey of Liquid Crystals Anisotropy properties LC Displays Other Applications

3 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)

4 Liquid Crystals state of matter between liquid and solid ( not isotropic, but liquid ) discovered by Friedrich Reinitzer in 1888 ( first sample was cholesteryl benzonate ) 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)

5 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

6 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

7 Aminoacids in Life are counterclockwise Chirality: Eutomers / Distomers 2001, Hazen+Filley: separation of aminoacids at calzit

8 LC-Examples cigar shaped: discotic: banana:

9 Director Orientation director orientation minimizes the free energy total Energy: E T = E elast +E electric +E interface E elast = E interface = E electric =

10 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)

11 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!

12 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%)

13 waveguiding in helical state, LC is sequence of polarizers cos n (90 /n), n>>100 Waveguiding

14 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

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16 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)

17 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

18 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

19 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

20 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)

21 LC-Videos Collapse Oscilation

22 Notes LCD $15b annual industry world-wide References: servlet/pb/show/ /aktiv-matrix_deutsch.pdf Fachlexikon ABC Chemie", Ed.: Hans-Dieter Jakubke and Hans Jeschkeit, Frankfurt am Main 1987, Band 1, p