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Liquid crystals Conducting polymers Molecular conductors, superconductors Molecular electronics

Liquid crystals Conducting polymers Molecular conductors, superconductors Molecular electronics Nanomaterials. More detailed presentations on Conducting Polymers and Nanomaterials are also available on the website. Liquid crystals. Discovery: 1888 – Friedrich Reinitzer

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Liquid crystals Conducting polymers Molecular conductors, superconductors Molecular electronics

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  1. Liquid crystals • Conducting polymers • Molecular conductors, superconductors • Molecular electronics • Nanomaterials More detailed presentations on Conducting Polymers and Nanomaterials are also available on the website

  2. Liquid crystals

  3. Discovery: • 1888 – Friedrich Reinitzer • (Institute of Plant physiology, University of Prague) • working on cholesteryl benzoate • solid  cloudy liquid  clear liquid • contacted Otto Lehmann (a German physicist) • recognized the ‘cloudy liquid’ as a new state • called it ‘liquid crystal’ (1904) 145.5oC 178.5oC

  4. Types of liquid crystals Director, n Nematic n n n n Chiral nematic n n n Smectic C Smectic A

  5. S. Chandrasekhar & coworkers Bangalore Nematic discotic Hexagonal columnar discotic

  6. Anisotropic properties Dielectric anisoptropy, Birefringence, Polarizability anisoptropy,  dielectric permittivity n  refractive index e  extraordinary [electric vector parallel to optic axis] o  ordinary [electric vector normal to optic axis]  polarizability

  7. Twisted nematic effect: Displays

  8. Reflector P2 E2 LC E1 P1 Courtsey: http://en.wikipedia.org/wiki/File:LCD_layers.svg

  9. Evolution of molecular design for LC Chemical instability Strong colour, Negative  Colour

  10. Conducting polymers

  11. Natural polymers

  12. Polytetrafluoroethylene (Teflon) Polyethylene Phenol-formaldehyde (Bakelite) Polyhexamethylene adipamide (Nylon 6,6) Polycarbonate Polyethyleneterephthalate (PET) Synthetic polymers

  13. Acetylene gas Ti(OBu)4 & Et3Al Toluene –78oC Ti(OBu)4 & Et3Al Hexadecane 150oC silvery film trans-polyacetylene Discovery of conducting polymers 1862 Lethby (College of London Hospital) Oxidation of aniline in sulfuric acid 1970’s Shirakawa (Japan) copper-coloured film cis-polyacetylene

  14. Polyacetylene (PA) Electrical conductivity () cis PA 10-10 – 10-9 S cm-1 trans PA 10-5 – 10-4 S cm-1 For comparison :  (copper) ~ 106 S cm-1 :  (teflon) ~ 10-15 S cm-1

  15. Semiconductor s ~ 10-5S cm-1 - e- + e- Metal s ~ 104S cm-1 Doping leads to enhanced conductivity

  16. Discoverers - Nobel Prize 2000 A. Heeger, A. McDiarmid, H. Shirakawa (this photograph taken at the International Conference on Synthetic Metals, 2000, was kindly provided by Prof. Heeger)

  17. Polyacetylene - electronic structure -electronic energy levels and electron occupation (d) regular trans-PA (e) dimerised trans-PA (a) ethylene (b) allyl radical (c) butadiene

  18. Examples of conducting polymers

  19. Copper 10+6 Platinum Bismuth 10+4 Graphite 10+2 100 Germanium Conducting Polymers 10-2 10-4 Silicon 10-6 10-8 10-10 10-12 Diamond 10-14 10-16 Quartz S cm-1 10-18 Electrical conductivities Polyethylene

  20. Applications of conducting polymers Polyaniline (PANI) Transparent conducting electrodes Electromagnetic shield Corrosion inhibitor ‘Smart windows’ (electrochromism) Polypyrrole (Ppy) Radar-invisible screen coating (microwave absorption) Sensor (active layer) Polythiophene (PT) Field-effect transistor Anti-static coating Hole injecting electrode in OLED Polyphenylenevinylene (PPV) Active layer in OLED

  21. Molecular conductors, superconductors

  22. TTF-TCNQ  = 105 S cm (58 K)

  23. Organic superconductors (TMTSF)2X X = ClO4-TC = 1.2 K (6.5 kbar) = PF6-TC = 1.4 K (ET)2X X = Cu(NCS)2-TC = 11.4 K

  24. Oxidation of donor / Reduction of acceptor

  25. Partial ionicity

  26. Peierl’s instability

  27. Organic donor molecules

  28. Organic acceptor molecules

  29. Molecular electronics

  30. Molecular Rectifier

  31. Molecular Amplifier 100 mV 20 mV Vin, Vout : input and output voltage, VP : bias voltage RP : polarisation resistance, RL : load resistance X : capacitor to isolate external circuit from bias voltage

  32. Nanomaterials

  33. Nanomaterials • Nanoscale • Size matters ! • Unique effects • Concept of Molecules • Metal nanoparticles • Parallels with molecules

  34. Chemical Composition CuSO4.5H2O K2Cr2O7 NiCl2.6H2O

  35. Structure Carbon Graphite Diamond Fullerene (C60)

  36. Properties of materials depend upon : Chemical composition Structure

  37. Size Silicon Chemical composition Structure Identical millimeter Silicon micrometer nanometer

  38. 1 cm 2 cm 1 nm 8 Surface area of 1 cube = 6 cm2 Surface area of 8 cubes = 48 cm2 Surface area = 6 x 22 = 24 cm2 1021 Total surface area = 6 x 1021 nm2 = 6 x 107 cm2 = 6000 m2 = 1.5 acre

  39. DNA 2.5 nm STEM image of a single layer of graphite - graphene Scale bar = 2 nm

  40. AFM image of a monolayer of surfactants Thickness = 2.5 nm Atomic Force Microscope

  41. Top-down Bottom-up

  42. Sequential extraction of adsorbed atoms - one by one - from Germanium surface Dujardin, G., Mayne, A., Robert, O., Rose, F., Joachim, C., and Tang, H. Science 1998, 251, 1206.

  43. Michael Faraday P CS2 AuCl3 Au 1791 - 1867 ‘finely divided metallic state’ of gold (M. Faraday, Philos. Trans. R. Soc.London, 1857, 147, 145)

  44. Dramatic change in Colour

  45. Plasmon Resonance Absorption

  46. Increasing particle size Same chemical composition but colour changes with size ! Quantum dots, nanoparticles of semiconductors, of different sizes, illuminated by a single light source, emit intense fluorescence of different colours (Felice Frankel, MIT)

  47. Fluorescence imaging in medical diagnostics Rat vasculature injected with water solution of Quantum Dots (CdSe-ZnS) Excitation at 780 nm 2-photon fluorescence at 550 nm Larson et al, Science 2003, 300, 1434 Using conventional fluorescent dyes

  48. Nanotechnology and Industry • Computing, data storage and communication • Materials • Manufacturing industry • Health & medicine • Energy & environment • Transportation & space exploration

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