Transcript Document

Introduction to Liquid Crystals
Chang-Kui Duan
2015/7/7
Chang-Kui Duan, Institute of
Modern Physics, CUPT
Contents
0. History of LC and LCD
1. Fundamentals
2. Molecular structure and Chemical Composition
3. Electronic Properties
4. Lyotropic, Polymeric, and Thermotropic Liquid
Crystals
5. Mixtures and Composites
6. Liquid Crystal Cells and Sample Preparation
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Liquid Crystal Displays (LCDs)
Innovation Timeline

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1888-1899
 1888, Austrian Botanist
Freidrich Reinitzer
discovers liquid
crystals
 1897,German scientist
Karl Braun invents the
cathode ray tube (CRT)
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Liquid Crystal Displays (LCDs)
Innovation Timeline

1900-1970
 1958, The first paper
research about LCD in
the U.S. wrote by Dr.
Glenn Brown
 1963, Richard Williams
and George Heilmeier
suggested using liquid
crystal materials for
display
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Liquid Crystal Displays (LCDs)
Innovation Timeline

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1900-1970
 1967, James Fergason
discovered the "twisted
nematic" LCD. He
produced the first
practical displays
 1968, RCA group had a
display based on the
dynamic scattering mode
(DSM) of liquid crystals
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Liquid Crystal Displays (LCDs)
Innovation Timeline

1970-1980
 1972,International Liquid
Crystal Company (ILIXCO)
produced the first modern
LCD watch using
Fergason Ideal
 1973, ,Sharp produced
the first portable
calculator, using a DSM
LCD screen
 1979, Walter Spear and
Peter LeComber made
the first color display
using lightweight thin film
transfer (TFT) LCD
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Liquid Crystal Displays (LCDs)
Innovation Timeline

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1980- 2000
 1985, Seiko-Epson
unveiled the first
commercial LCD color
TV set, which had a 2
inch view
 1992, Sharp developed a
multimedia-compatible
16.5 inch color TFT LCD,
that was the world's first
LCD ViewCam
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Liquid Crystal Displays (LCDs)
Innovation Timeline

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2000- Present
 2004, Philips
demonstrated a 20″ 3-D
LCD at CeBIT in
Hannover
 2005, Samsung
Developed World's
Largest (82") Full HDTV
TFT-LCD
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Other LCD application: LCD
Projector
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Digital Light Processing™ (DLP)
Projector
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1. Fundamentals
States of Matter
What is Liquid Crystal?
Classification
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States of Matter
Solid
Liquid crystal
“fourth state of matter”
Liquid
Gas
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Images: MacDonald, R. “Liquid Crystals Fascinating State of Matter or "Soft is beautiful".
Chang-Kui Duan, Institute of
Accessed 7-2006
Modern Physics, CUPT
What is a Liquid
Crystal?
Liquid Crystal – a stable phase of
matter characterized by anisotropic
properties without the existence of a
3-dimensional crystal lattice –
generally lying between the solid
and isotropic (“liquid”) phase.
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Isotropic
Liquids and gases
(uniform properties in all
directions).
vs.
Anisotropic
Liquid Crystals
have orientational order
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Liquid Crystal Model
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Classifications
Lyotropic, Polymeric, and Thermotropic Liquid
Crystals
 Nematic, cholesteric, smectic, and ferroelectric.
 Small molecular, polymer

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2. Molecular structure and
Chemical Composition

A side chain R, two or more aromatic rings A and
A’, connected by linkage groups X and Y, and at
the other end connected to a terminal group R’.
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Examples
N-(4- Methoxybenzylidene)-4-butylaniline
(MBBA) molecule
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Consequence



All the physical and optical properties of liquid crystals are
governed by the properties of these constituent groups and
how they are chemically synthesized together: Dielectric
constants, elastic constants, viscosities, absorption spectra,
transition temperatures, existence of mesophases,
anisotropies, and optical nonlinearities
Molecules are quite large and anisotropic, practically
impossible to treat all the possible variations in the
molecular architecture and the resulting changes in the
physical properties.
Some generally applicable observations on the
dependence of the physical properties on the molecular
constituents.
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Chemical stability
Depends on the central linkage group
 Schiff-base unstable
 Ester, azo, and azoxy stable, but are also quite
susceptible to moisture, temperature change, and
ultraviolet (UV) radiation.
 Compounds without a central linkage group are
among the most stable liquid crystals ever synthesized.
 Other compounds such as pyrimide and
phenylcyclohexane are also quite stable.
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3. Electronic Properties
Decided by they constituent molecules
 Energy level structures rather complex
 Theories are still not sufficiently precise in relating
the molecular structures and the liquid crystal
responses.
 Limit here to stating some of the well-established
results, mainly from molecular theory and
experimental observations.

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energy levels or orbitals of aromatic
rings
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Characteristic
Very Absorptive in UV ( < ~ 200 nm)
 Quite transparent in Vis and IR (0.4-5 m)
 Far IR (>=9 m), very absorptive due to
rovibrational transitions

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4. Lyotropic, Polymeric, and
Thermotropic Liquid Crystals
Lyotropic Liquid Crystals are obtained when an
appropriate concentration of a material is
dissolved in some solvent; Ex: Soap; Are of
interest in biological studies.
 Polymeric Liquid Crystals are basically the
polymer versions of the monomers

Refer to the 1.3.1 and 1.3.2
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Thermotropic Liquid
Crystals
Most widely used and extensively studied
Liquid Crystals
 There are 3 basic phases : Nematics,
Cholesterics, and Smectics

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Liquid Crystal Phases
Nematic,
Smectic & Cholesteric
Anisotrpic substances may go through one or
several Liquid Crystal Phases
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Nematic and Cholesteric
Namatic
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Cholesteric
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Smectic-A and Smectic-C
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Smectic C* (ferroelectric) and
unwounded Smectic C*
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4. Mixtures and Composites
temperature ranges for pure liquid crystals are
quite limited.
 Industrial applications employ mostly mixtures,
composites, or doped liquid crystals with tailormade physical and optical properties.
 The optical properties, dielectric anisotropies, and
viscosities are very different from those of the
individual mixture constituents.
 Creating mixtures is an art, guided of course by
some scientific principles.

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Mixtures
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Dye-Doped Liquid Crystals

Modification of their well-known linear, and more
recently observed nonlinear, optical properties
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Polymer-Dispersed Liquid
Crystals

See textbook 1.4.3
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5. Liquid Crystal Cells and
Sample Preparation
The alignment of the liquid crystal axis in cells is
essentially controlled by the cell walls, whose
surfaces are treated in a variety of ways to
achieve various director axis alignments.
 Bulk Thin Film
 Liquid Crystal Optical Slab Waveguide, Fiber,
and Nanostructured Photonic Crystals

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Bulk Thin Film
For procedure
to prepare,
see 1.5.1
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
Liquid Crystal Optical Slab Waveguide, Fiber,
and Nanostructured Photonic Crystals

1.5.2 for details
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Order Parameter, Phase
Transition,and Free Energies
The contents of next chapter!
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Chang-Kui Duan, Institute of
Modern Physics, CUPT