Thermodynamics and quantum physics
Report’s topic: liquid crystal
Group’s
members;
Name
Student ID
Nguyễn Nhựt Khanh
2151097
Bùi Đức Tiến
2151263
Nguyễn Thanh Yến Thy
2151034
Table of contents
01
Introduction
02
Classification of Liquid Crystals
03
Characteristics and Classification
04
Applications
INTRODUCTION
There are commonly three kinds of distinct states, which
are:
However, there exists a material that is not alike those
mentioned above.
History
In 1888, while experimenting with cholesteryl benzoate,
Friedrich Reinitzer discover the liquid crystal phase
(mesophase or mesogenic phase).
Cholesteryl benzoate’s structure.
Friedrich Reinitzer (1857-1927)
Austrian botanist.
In Reinitzer’s 1888 experiment,
cholesteryl benzoate had 2
melting points.
LC is an intermediate
state lying between solid
and liquid.
LC materials melt twice or more as
temperature rises.
A substance blending the structures
of liquid and crystalline solid.
Molecules move
randomly and rotate
about all directions.
What is basically liquid
crystal?
Molecules are ordered,
occupy in a particular
position, point along fixed
axes.
Mesogens: Liquid-crystalforming molecules are
rod-like, dics-like or
banana-like molecules.
CLASSIFICATION OF
LIQUID CRYSTAL PHASES
THERMOTROPIC LIQUID
CRYSTAL
Obtained by thermally induced
Put into two types:
- Enantiotropic – both heating and
cooling
- Monotropic – either heating or
cooling
LYOTROPIC LIQUID CRYSTAL
Formed by dissolving the compound
in an appropriate solvent
CLASSIFICATION OF
LIQUID CRYSTAL PHASES
There are 2 main types of subphases in Thermotropic LC phase: Nematic and
Smectic.
NEMATIC PHASE
•
Nematic phase does not have a certain order.
•
The alignment will change based on the electric or magnetic field surrounding it.
SMECTIC PHASE
•
Appear under soap form, have a
translational order, align
themselves in layers.
•
There are 3 main types of Smectic:
Perpendicular to smectic plane
No particular positional order
Molecules are arranged into a
network of hexagons
Director is at a constant tilt angle
APPLICATIONS
Superhydrophobic surfaces, biological cell membrane.
CHARACTERISTICS
CHARACTERISTICS
Temperature effects
Electro-optic effects
Temperature effects
LCs are sensitive to temperature.
The colors of LCs change due to the decent temperature.
Temperature effects
When white light is directed at this stack of molecules, the
wavelength of light equals to this pitch distance is reflected
back.
Temperature effects
- At low temperature, red light is reflected back.
- At high temperature, blue light is reflected back.
Temperature effects
- Each LC has only a few degrees of temperature where the
organization is such that light is reflected back.
- On either side of this temperature range, all light are absorbed
and the LC turns black.
Electro-optic effects
- It is one of the most common characteristics of LCs forming a basis
for inventing LCDs.
- When optically active materials, such as liquid crystals, are placed
between polarizing filters crossed in this manner, some light may get
through.
- The light is fully blocked when the director lies parallel to one filter
or the other.
Electro-optic effects
- In normally white mode, the light polarization is
changed by the helix until it matches the orientation
of the front polarizer.
- If the light polarization isn’t changed, it cannot pass
through front polarizer. Hence, there will be normal
black mode.
APPLICATIONS
LCs have a wide variety of applications, from artificial products to natural products
Nanotube, Cell membrane, Storage data using liquid crystals, Sensor using liquid
crystals
APPLICATIONS
The most well-known application of this unique state
is liquid crystal display (aka LCD).
00
01
02
APPLICATIONS - History
00
Richard Williams found that
liquid crystals had electro optic characteristics.
This discovery has set up the
foundation for the first LCD in
the next few years.
01
02
APPLICATIONS - History
00
In 1927, Vsevolod Frederiks
devised the electrically switched
light valve, called the
Fréedericksz transition, the
essential effect of all LCD
technology.
01
02
APPLICATIONS - History
00
In 1964, based on the effect
discovered by Williams,
George H. Heilmeier invented
dynamic scattering mode
display (DSM display), the first
operation of LCD.
01
02
APPLICATIONS – Operating Principle of LCD
There are 3 requirements:
1. Controlled by changing the applied current.
2. Use polarized light.
3. Able to transmit or change the polarized light.
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01
02
APPLICATIONS – Operating Principle of LCD
Backlights are the only lights on the monitor and they always open.
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02
APPLICATIONS – Operating Principle of LCD
These sheets help the backlights emerging out of the front.
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02
APPLICATIONS – Operating Principle of LCD
2 films are placed to reduce the dot pattern and increase the
perpendicular light rays.
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02
APPLICATIONS – Operating Principle of LCD
The critical part of LCDs is the polarized glasses.
The sheets are placed perpendicularly -> the lights pass through.
When rotating the upper one 90 degrees -> the light will be
blocked.
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01
02
APPLICATIONS – Operating Principle of LCD
The screen cannot be rotated, but we can decide which lights are
allowed to pass through by changing its angle.
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02
APPLICATIONS – Operating Principle of LCD
Sandwich of glass - helping the monitor produce the colors.
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