The photoactivity is attained either by
introducing photoactive group in liquid
crystalline polymer or the polymer inherently possess both the properties.
The physical change such as isomerization of specific moiety is reversible.
The chemical change such as crosslinking is usually irreversible or in some
cases reversible.
Example of photoactive moiety
Azo, spiropyrans, -C=C-, etc.
Introduction
Photo-controlled and photo-switchable materials based on liquid crystals (LC) are
finding application in many areas such as colored information recording, photooptical triggers, and display units and more (Barth et al. 2005). It is well-known that
optical and electrical properties are strongly associated with orientation and morphology of these polymers (Rajaram et al. 1996). Liquid crystal has shown increasing interest because of their self-assembling behavior and also natural ability to
dramatically alter the properties of light reflected from or transmitted through
the assembly. After the photoinduction phenomenon came to the knowledge of the
researcher, it was quickly understood that incident light itself can control
the molecular ordering or disordering of liquid crystalline system. This has become
the basis for controlling system with light or “light control light” and the gate opened
for high speed information processing.
The photoactivity normally originates from photoactive groups having the ability
to isomerize or in some cases form cross-links. Few common photochromic moieties
with their photoactivity modes are described in Fig. 1.
During UV radiation the original stable linear trans-isomer converts to bent Cisisomer, which disturbs the LC arrangement and phase transition occurs to iso-phase.
The trans-isomer reappears after discontinuing the radiation, which is due to back
isomerization triggering reassembly to LC phase (Fig. 2).
On heating the LC structure crosses the LC-Isotropic (LC-iso) transition temperature. AS described above the phenomenon is similar during UV radiation. Either
radiation or heating discontinued the original LC phase reappears. During cooling,
the temperature goes below LC-iso transition temperature and LC phase reappears.
Light is considered as most interesting and convenient among various stimulating
sources, as it is a clean energy and can be manipulated conveniently and controlled
precisely. This adds additional dimension to the system of phase transition trigger.
The polymer system having both liquid crystalline moiety (rod-shaped; mesogen)
and photoactive moiety gives numerous possibilities, e.g., photochromic group, such
as azo can be chemically attached creating various architectures, or it can be
dissolved in LC polymer (LCP) to make an azo doped structures. It can also be LC
molecule is controlled by azo polymer. The other molecular designs can be based on
14 Photoactive Liquid Crystalline Polymers
393
introducing photoactive group in liquid
crystalline polymer or the polymer inherently possess both the properties.
The physical change such as isomerization of specific moiety is reversible.
The chemical change such as crosslinking is usually irreversible or in some
cases reversible.
Example of photoactive moiety
Azo, spiropyrans, -C=C-, etc.
Introduction
Photo-controlled and photo-switchable materials based on liquid crystals (LC) are
finding application in many areas such as colored information recording, photooptical triggers, and display units and more (Barth et al. 2005). It is well-known that
optical and electrical properties are strongly associated with orientation and morphology of these polymers (Rajaram et al. 1996). Liquid crystal has shown increasing interest because of their self-assembling behavior and also natural ability to
dramatically alter the properties of light reflected from or transmitted through
the assembly. After the photoinduction phenomenon came to the knowledge of the
researcher, it was quickly understood that incident light itself can control
the molecular ordering or disordering of liquid crystalline system. This has become
the basis for controlling system with light or “light control light” and the gate opened
for high speed information processing.
The photoactivity normally originates from photoactive groups having the ability
to isomerize or in some cases form cross-links. Few common photochromic moieties
with their photoactivity modes are described in Fig. 1.
During UV radiation the original stable linear trans-isomer converts to bent Cisisomer, which disturbs the LC arrangement and phase transition occurs to iso-phase.
The trans-isomer reappears after discontinuing the radiation, which is due to back
isomerization triggering reassembly to LC phase (Fig. 2).
On heating the LC structure crosses the LC-Isotropic (LC-iso) transition temperature. AS described above the phenomenon is similar during UV radiation. Either
radiation or heating discontinued the original LC phase reappears. During cooling,
the temperature goes below LC-iso transition temperature and LC phase reappears.
Light is considered as most interesting and convenient among various stimulating
sources, as it is a clean energy and can be manipulated conveniently and controlled
precisely. This adds additional dimension to the system of phase transition trigger.
The polymer system having both liquid crystalline moiety (rod-shaped; mesogen)
and photoactive moiety gives numerous possibilities, e.g., photochromic group, such
as azo can be chemically attached creating various architectures, or it can be
dissolved in LC polymer (LCP) to make an azo doped structures. It can also be LC
molecule is controlled by azo polymer. The other molecular designs can be based on
14 Photoactive Liquid Crystalline Polymers
393