considerable mobility. They show a reversible phase transition and shape change
when certain external stimuli such as heat, light, electric, and magnetic fields are
applied. When the molecules are heated from the aligned LC phase to the isotropic
phase, the conformational rearrangement triggers the macroscopic mechanical deformation. The electric and magnetic field can reorient the LC director inside the
network. To induce the large amplitude of dimensional change, the molecular
mobility should be sufficiently high. Generally, the phase transition temperature of
the elastomers is low because of the existence of flexible units. The LCE can be
roughly classified as the side-chain LCE, the main-chain LCE, and the combined
system (Finkelmann et al. 1981). The side mesogenic groups may lie parallel or
perpendicular to the main-chain director depending on the spacer length. Uniaxial
alignment of LCE is generally achieved by two steps. A weakly cross-linked LC gel
composed of the polymer backbone and mesogenic units is uniaxially aligned by the
external stimuli, and then the second cross-linking takes place in order to preserve
the order. Various elastomers have been reported on the basis of nematic (N), chiral
nematic (NÃ), and smectic (Sm) phases.
Recent Interests and Applications
Alignment Media
The key advantage of densely cross-linked anisotropic LC films is based on the longterm stability of uniaxial alignment. The macroscopic orientation of the LC molecules is achieved by the polymerization of multifunctional RM in contact with the
unidirectionally rubbed substrates or under external forces. The rod-shaped RMs are
usually aligned along the rubbing direction, where the interaction between the LC
molecules and the aligning surface determines the alignment direction. The polyimide-based alignment layers have been conventionally used because of the excellent chemical resistance, thermal stability, and transparency (Lee et al. 2012).
However, the mechanical contact method causes the serious drawbacks such as
unstable electric charges, residual stresses, and dust particles, which can deteriorate
the electrical and optical performances of LC devices.
To overcome those drawbacks, the photo-alignment methods have been
suggested. Photochromic azobenzene-based RM may align parallel to the
Fig. 3 Schematic diagrams of conceptual LC elastomers and thermosets
100
D.-Y. Kim et al.
when certain external stimuli such as heat, light, electric, and magnetic fields are
applied. When the molecules are heated from the aligned LC phase to the isotropic
phase, the conformational rearrangement triggers the macroscopic mechanical deformation. The electric and magnetic field can reorient the LC director inside the
network. To induce the large amplitude of dimensional change, the molecular
mobility should be sufficiently high. Generally, the phase transition temperature of
the elastomers is low because of the existence of flexible units. The LCE can be
roughly classified as the side-chain LCE, the main-chain LCE, and the combined
system (Finkelmann et al. 1981). The side mesogenic groups may lie parallel or
perpendicular to the main-chain director depending on the spacer length. Uniaxial
alignment of LCE is generally achieved by two steps. A weakly cross-linked LC gel
composed of the polymer backbone and mesogenic units is uniaxially aligned by the
external stimuli, and then the second cross-linking takes place in order to preserve
the order. Various elastomers have been reported on the basis of nematic (N), chiral
nematic (NÃ), and smectic (Sm) phases.
Recent Interests and Applications
Alignment Media
The key advantage of densely cross-linked anisotropic LC films is based on the longterm stability of uniaxial alignment. The macroscopic orientation of the LC molecules is achieved by the polymerization of multifunctional RM in contact with the
unidirectionally rubbed substrates or under external forces. The rod-shaped RMs are
usually aligned along the rubbing direction, where the interaction between the LC
molecules and the aligning surface determines the alignment direction. The polyimide-based alignment layers have been conventionally used because of the excellent chemical resistance, thermal stability, and transparency (Lee et al. 2012).
However, the mechanical contact method causes the serious drawbacks such as
unstable electric charges, residual stresses, and dust particles, which can deteriorate
the electrical and optical performances of LC devices.
To overcome those drawbacks, the photo-alignment methods have been
suggested. Photochromic azobenzene-based RM may align parallel to the
Fig. 3 Schematic diagrams of conceptual LC elastomers and thermosets
100
D.-Y. Kim et al.