concentration, a low cross-linker concentration allows optimization of the photoinduced
deformation of cross-linked LC polymers.
These photomobile materials can find widespread applicability because they can
be controlled remotely just by manipulating the irradiation conditions. The mechanical motion can be reversed by irradiation with different light, mostly the visible
light. The reverse process is related to the reversing of trans-cis photoisomerization.
As cis-isomer is basically not stable, it reverses back to trans-isomer by white light,
heat, and even in dark (slow).
By using multiple inks, microactuators with different subunits are realized, which can
be addressed individually by varying wavelength of radiation (van Oosten et al. 2009).
The actuator performance mimics the motion of natural cilia. These artificial cilia are
able to create flow and mixing in wet environments such as lab-on-a-chip applications.
The roll-to-roll fabrication is possible with development of supporting technologies and
large-scale, low-cost production of miniaturized active polymer systems.
A light-driven plastic motor can be prepared from a bilayer plastic belt made from
a photoactive liquid crystalline elastomer (LCE) laminated on polyethylene film and
connecting both ends of the film (Yamada et al. 2008). The belt after placing on a
pulley system is irradiated simultaneously with UV light from one side and
visible light from other side. The belt is found to rotate and pulleys were driven.
The irradiation of UV light-triggered contraction and visible light-produced
expansion initiating clockwise and counterclockwise motion set the belt in
rotational motion.
Liquid Single Crystal Elastomers (LSCEs)
The LSCEs make a subclass of liquid crystalline elastomers. Usually, the mesogens
in liquid crystalline polymers do not remain in monodomain state. The LCP needs to
be in monodomain state, particularly in display. The quality remains inferior for
multidomain state. Attempts are always there to design monodomain LCE. The
successful strategy in the synthesis methodology of LSCEs forces all the mesogen to
attain monodomain structure. The LSCEs consist of weakly cross-linked polymer
networks having macroscopic orientation of the director, n.
The synthesis and study of azobenzene-containing LSCEs as light-driven artificial
muscle-like actuators are very active. A typical synthesis method involves three stages,
e.g., a stable elastomeric system is made which can be handled properly. This can be
achieved by partial cross-linking. In the second stage, the orientation of all different
directors of the entire sample is executed by applying uniaxial force to the sample
along its longest axis. After suitable time, a monodomain LCE is obtained, which is
called as a LSCE and is perfectly transparent. In the third stage, the created anisotropic
state is fixed by a second cross-linking reaction without removing the applied force.
The search for easier methods is prompted by successful application in photonic
devices. Macroscopically ordered monodomain smectic-like lamellar structure with
orientational order and positional order can be assembled by linear polarized light
irradiation (473 nm, 20 mW/cm
2 ) at room temperature (Liu et al. 2011).
14 Photoactive Liquid Crystalline Polymers
405
deformation of cross-linked LC polymers.
These photomobile materials can find widespread applicability because they can
be controlled remotely just by manipulating the irradiation conditions. The mechanical motion can be reversed by irradiation with different light, mostly the visible
light. The reverse process is related to the reversing of trans-cis photoisomerization.
As cis-isomer is basically not stable, it reverses back to trans-isomer by white light,
heat, and even in dark (slow).
By using multiple inks, microactuators with different subunits are realized, which can
be addressed individually by varying wavelength of radiation (van Oosten et al. 2009).
The actuator performance mimics the motion of natural cilia. These artificial cilia are
able to create flow and mixing in wet environments such as lab-on-a-chip applications.
The roll-to-roll fabrication is possible with development of supporting technologies and
large-scale, low-cost production of miniaturized active polymer systems.
A light-driven plastic motor can be prepared from a bilayer plastic belt made from
a photoactive liquid crystalline elastomer (LCE) laminated on polyethylene film and
connecting both ends of the film (Yamada et al. 2008). The belt after placing on a
pulley system is irradiated simultaneously with UV light from one side and
visible light from other side. The belt is found to rotate and pulleys were driven.
The irradiation of UV light-triggered contraction and visible light-produced
expansion initiating clockwise and counterclockwise motion set the belt in
rotational motion.
Liquid Single Crystal Elastomers (LSCEs)
The LSCEs make a subclass of liquid crystalline elastomers. Usually, the mesogens
in liquid crystalline polymers do not remain in monodomain state. The LCP needs to
be in monodomain state, particularly in display. The quality remains inferior for
multidomain state. Attempts are always there to design monodomain LCE. The
successful strategy in the synthesis methodology of LSCEs forces all the mesogen to
attain monodomain structure. The LSCEs consist of weakly cross-linked polymer
networks having macroscopic orientation of the director, n.
The synthesis and study of azobenzene-containing LSCEs as light-driven artificial
muscle-like actuators are very active. A typical synthesis method involves three stages,
e.g., a stable elastomeric system is made which can be handled properly. This can be
achieved by partial cross-linking. In the second stage, the orientation of all different
directors of the entire sample is executed by applying uniaxial force to the sample
along its longest axis. After suitable time, a monodomain LCE is obtained, which is
called as a LSCE and is perfectly transparent. In the third stage, the created anisotropic
state is fixed by a second cross-linking reaction without removing the applied force.
The search for easier methods is prompted by successful application in photonic
devices. Macroscopically ordered monodomain smectic-like lamellar structure with
orientational order and positional order can be assembled by linear polarized light
irradiation (473 nm, 20 mW/cm
2 ) at room temperature (Liu et al. 2011).
14 Photoactive Liquid Crystalline Polymers
405