Example of PDLC architectural window

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Example of PDLC architectural window
Rest State
Activated State
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Polymer Dispersed Liquid Crystal (PDLC)
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Chapter 2. Polymer Liquid Crystals
2.1. Liquid Crystalline Phases
Mesophase a phase lying between solid (crystal)
and isotropic (liquid) states. Liquid crystals
fluid (l) but also show birefringence (c) have
properties associated with both crystals and
liquids. Thermotropic liquid crystalline phase
is formed when the pure compound is
heated. Lyotropic liquid crystalline phase
forms when the molecules are mixed with a
solvent (solution).
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(a)
(b)
Fig 9.3 The structure of (a) nematic and (b)
Columnar discotic phases.
ISOTROPIC LIQUID
SOLID
MESOPHASE
3D order
1or 2D order
NONE
Mesogen Smectogen Nematogen Lamellar Non-lamellar
Fig 9.2 The structure of molecules which form (a)
calamitic and (b) discotic liquid
crystalline
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pitch
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Molecular structure rigid, long lathe-like
shapes with a high length to breadth ratio, or
disc shapes. Chemical structure composed of a
central core comprising aromatic or
cycloaliphatic units by rigid links and having
either polar or flexible alkyl and alkoxy
terminal groups. Molecular design of liquid
crystalline polymers (1) Incorporation of
mesogens into chain-like structures by linking
them together through both
terminal units to form main-chain
liquid crystalline polymers. (2) Attachment of
mesogens through one terminal unit to a polymer
backbone to produce a side chain
comb-branch structure. (3) A combination of
both main and side chain structures.
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Thermotropic LC Molecule
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The mesogenic units in a polymer can form ordered
structures characterized by long-range
orientational order, with the long axes of the
mesogenic groups arranged in one preferred
direction of alignment called the director. The
lateral forces between the molecules in the
smectic phases are stronger than the forces
between the layers. In the nematic phase, while
the directional ordering of the mesogen long axes
is maintained, the centers of gravity are no
longer confined in layers, but are distributed
randomly in the phase. A chiral center imparts a
twist to each successive layer in the cholesteric
phase where the orientation of the director
changes regularly from layer to layer, forming a
helical arrangement of the directors in three
dimensional space.
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• In main chain liquid crystal polymers, there is
  usually a transition from crystal to a mesophase,
  whereas in more amorphous systems when a glass
  transition is present. The mesophase may appear
  after this transition has occurred.
• In multiple transition thermotropic systems, the
  increase in temperature leads changes from the
  most ordered to the least ordered states.
• k crystal, g glass, i isotropic
• S smectic (S chiral S), N nematic (N
  chiral N)
• Ch cholesteric
• 2.2 Identification of the Mesophases
• By polarized optical microscope (POM)
• Nematic phases e.g. Schlieien texture, threaded
  texture,
• and marbled texture.

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• Smectic phases e.g. focal conic and fan
  texture, mosaic texture, and broken focal conic
  texture.
• Cholesteric phases e.g. Grandjear texture.

By differential scanning calorimeter(DSC)

• Widely used for detecting temperatures of
  thermotropic
• mesophase transitions.
• First-order transitions.

By X-ray diffraction (XRD)

• For the least ordered phases, one diffuse halo
  is seen at large diffraction angles.
• At smaller diffraction angles, a diffuse inner
  ring is formed in nematic samples.
• When the smectic phases are present, one or more
  sharp inner rings, arising from the more ordered
  lamellar structure, are seen.

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  Nematic Schlieren texture
SmA fan-shaped texture
SmA focal conic texture
Nematic Phase (threaded)
Mosaic texture of a hexatic SmB phase
Nematic Phase (marbled)
SmC Schlieren texture and focal conic
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