RM may form three-dimensional (3D) networks without disrupting the molecular
order in a monomeric phase, revealing the enhanced thermal conductivity.
Optical Polarizers for Color Tunable Film
Birefringent film is suitable to change the polarization state of polarized light.
Several literatures have dealt with the properties of the cross-linked NÃ networks.
The reflective polarizer for circularly polarized light can be easily converted into
linearly polarized light by addition of the cholesteric layer. Reflection wavelength is
determined by adjusting the content of chiral RM within the anisotropic media and
the final morphology. A single-pitch NÃ-LC reflects circularly polarized light of the
same handedness, while outside the reflection band, all polarization states are
transmitted. The cross-linked NÃ-LC optical films are useful for the formation of
polarized light. By changing the amount of chiral component, the reflection wavelength and the color are determined. Generally, the NÃ-LC film is effective to
implement a specific color rather than the whole visible spectrum. Introduction of
a gradient in pitch may increase bandwidth to the visible region. The different
reactivity of RMs at the same location induces the concentration gradient between
the upper and lower regions during the polymerization process (Fig. 6). The area
exposed to a strong UV light in the LC cell reveals fast conversion of chiral RM,
while the other side with a low intensity of UV light consumes less RM. Helical pitch
gradient is accompanied with broadening reflective wavelength due to the concentration change of chiral moieties. Decreasing the polymerization rate increases the
bandwidth. The helix gradient is permanently fixed by cross-linking of RM. The
NÃ-LC polymer networks have been widely used as color flop pigments or color
filters with a distinct viewing angle dependence.
Lyotropic mesophases are formed when the amphiphilic chromic LC molecules,
consisting of hydrophobic discotic or calamitic mesogenic cores and hydrophilic
ionic functions at the periphery of cores, are dissolved in aqueous solution (Bae et al.
2011). The electrons are rapidly transported along the long axis of the self-assembled
LLC columns, and additionally the oriented anisotropic film exhibits a selective light
absorption parallel to the in-plane of the discotic core of LLC. However, the
aqueous-based LLC films often cause the macroscopic cracks and defects during
the coating and drying processes. The LLC containing polymerizable monomers has
been used to fabricate the robust polarizers with high thermal, mechanical, and
chemical stability by spontaneous self-assembly and subsequent photopolymerization (Fig. 7). The patterned polarizers prepared by a lithographic method
may provide the new opportunities in the various application fields including
biosensors.
Photo- and Electroluminescence
The anisotropic LC networks can be used as active layers in polarized electroluminescence devices (Jose et al. 2011). The major advantage of RM is based on the high
solubility in a wider range of organic solvents before the cross-linking reaction and
the easy formation of mono-domain even at ambient temperature. Polymerization of
light-emitting RM may provide the full color displays by tailoring the active core
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D.-Y. Kim et al.
order in a monomeric phase, revealing the enhanced thermal conductivity.
Optical Polarizers for Color Tunable Film
Birefringent film is suitable to change the polarization state of polarized light.
Several literatures have dealt with the properties of the cross-linked NÃ networks.
The reflective polarizer for circularly polarized light can be easily converted into
linearly polarized light by addition of the cholesteric layer. Reflection wavelength is
determined by adjusting the content of chiral RM within the anisotropic media and
the final morphology. A single-pitch NÃ-LC reflects circularly polarized light of the
same handedness, while outside the reflection band, all polarization states are
transmitted. The cross-linked NÃ-LC optical films are useful for the formation of
polarized light. By changing the amount of chiral component, the reflection wavelength and the color are determined. Generally, the NÃ-LC film is effective to
implement a specific color rather than the whole visible spectrum. Introduction of
a gradient in pitch may increase bandwidth to the visible region. The different
reactivity of RMs at the same location induces the concentration gradient between
the upper and lower regions during the polymerization process (Fig. 6). The area
exposed to a strong UV light in the LC cell reveals fast conversion of chiral RM,
while the other side with a low intensity of UV light consumes less RM. Helical pitch
gradient is accompanied with broadening reflective wavelength due to the concentration change of chiral moieties. Decreasing the polymerization rate increases the
bandwidth. The helix gradient is permanently fixed by cross-linking of RM. The
NÃ-LC polymer networks have been widely used as color flop pigments or color
filters with a distinct viewing angle dependence.
Lyotropic mesophases are formed when the amphiphilic chromic LC molecules,
consisting of hydrophobic discotic or calamitic mesogenic cores and hydrophilic
ionic functions at the periphery of cores, are dissolved in aqueous solution (Bae et al.
2011). The electrons are rapidly transported along the long axis of the self-assembled
LLC columns, and additionally the oriented anisotropic film exhibits a selective light
absorption parallel to the in-plane of the discotic core of LLC. However, the
aqueous-based LLC films often cause the macroscopic cracks and defects during
the coating and drying processes. The LLC containing polymerizable monomers has
been used to fabricate the robust polarizers with high thermal, mechanical, and
chemical stability by spontaneous self-assembly and subsequent photopolymerization (Fig. 7). The patterned polarizers prepared by a lithographic method
may provide the new opportunities in the various application fields including
biosensors.
Photo- and Electroluminescence
The anisotropic LC networks can be used as active layers in polarized electroluminescence devices (Jose et al. 2011). The major advantage of RM is based on the high
solubility in a wider range of organic solvents before the cross-linking reaction and
the easy formation of mono-domain even at ambient temperature. Polymerization of
light-emitting RM may provide the full color displays by tailoring the active core
104
D.-Y. Kim et al.