cooled down into the LC phases. The elastic properties can be easily tailored by
varying the blending ratio between the polymer networks and LMWLC. Strong
intermolecular interaction may generate a residual orientation even above the isotropization temperature. Under an electric field, the LC director is reoriented,
modifying the dielectric and optical anisotropy of the cell. In contrast to polymerdispersed LC (PDLC) system in which polymer matrix is optically isotropic, the LC
gels are optically anisotropic. The optical axes of the polymer matrix and the LC are
parallel, so that macroscopically oriented anisotropic gels are transparent in
the offstate, irrespective of the angle of the incident light. The advantages of
anisotropic gels over the PDLC systems are their low viewing angle dependence
due to the refractive index matching between the LMWLC component and the
mesogenic moieties of the networks. Moreover, the relaxation of LC solvents is
faster since the mesogenic units in the polymer networks provide the internal director
field. The LC monomers used for anisotropic gels include N, NÃ, Sm, and ferroelectric materials (Artal et al. 2001). Polymer-stabilized LC (PSLC) is another
anisotropic LC gel system, where the concentration of polymer networks is less
than 10 wt % (Kemiklioglu et al. 2014).
Recent Interests and Applications
Alignment Modification and Electric Field-Induced Light Scattering
Incorporation of RMs in gels may not only provide new functionalities but also
improve a variety of properties of the final products. They are often used to modify
the surface properties of the substrate. Incorporation of a polymerizable group into a
gelator leads to the induction of phase-separated structure in the LC gels. As shown
in Fig. 12, when the homogeneous mixtures composed of reactive isoleucine
derivatives and a Sm LC are introduced into a cell, the fibers grow in a direction
perpendicular to the long axis of LC molecules (Kato et al. 2007). The anisotropic
structures of the oriented fibers are then stabilized by the photopolymerization of
methacryloyl moieties of the gelator. Upon heating above isotropization temperature
and then cooling to the room temperature, the LC is aligned along the groove
structures of the polymerized fibers. In display devices, the gel layers are employed
to amplify the low-tilting angles on the rubbed surfaces. In order to preserve the
amplified orientation, RMs in the gel are required.
Light transmission of the LC gels depends on the initial orientation and dielectric
anisotropy of LC. The uniaxially planar gels with a positive anisotropic LC or the
homeotropically aligned gels with a negative anisotropic LC may scatter the light
when an electric field is applied. The hydrogen-bonded molecules are preferentially
used as a LC gelator for the light scattering. As the temperature from I state
decreases, the fully dissolved gelator undergoes the micro-phase separation
from the LC media, and then the continuously self-assembled fiber networks are
formed. The finely dispersed fiber networks within the LC divide the LC molecules
into the small domains. Without applying an electric field, the LC cells completely
block the behind image because of the highly scattering states. As the voltage is
applied, the LC molecules are aligned perpendicular to the substrate plane, and
110
D.-Y. Kim et al.
varying the blending ratio between the polymer networks and LMWLC. Strong
intermolecular interaction may generate a residual orientation even above the isotropization temperature. Under an electric field, the LC director is reoriented,
modifying the dielectric and optical anisotropy of the cell. In contrast to polymerdispersed LC (PDLC) system in which polymer matrix is optically isotropic, the LC
gels are optically anisotropic. The optical axes of the polymer matrix and the LC are
parallel, so that macroscopically oriented anisotropic gels are transparent in
the offstate, irrespective of the angle of the incident light. The advantages of
anisotropic gels over the PDLC systems are their low viewing angle dependence
due to the refractive index matching between the LMWLC component and the
mesogenic moieties of the networks. Moreover, the relaxation of LC solvents is
faster since the mesogenic units in the polymer networks provide the internal director
field. The LC monomers used for anisotropic gels include N, NÃ, Sm, and ferroelectric materials (Artal et al. 2001). Polymer-stabilized LC (PSLC) is another
anisotropic LC gel system, where the concentration of polymer networks is less
than 10 wt % (Kemiklioglu et al. 2014).
Recent Interests and Applications
Alignment Modification and Electric Field-Induced Light Scattering
Incorporation of RMs in gels may not only provide new functionalities but also
improve a variety of properties of the final products. They are often used to modify
the surface properties of the substrate. Incorporation of a polymerizable group into a
gelator leads to the induction of phase-separated structure in the LC gels. As shown
in Fig. 12, when the homogeneous mixtures composed of reactive isoleucine
derivatives and a Sm LC are introduced into a cell, the fibers grow in a direction
perpendicular to the long axis of LC molecules (Kato et al. 2007). The anisotropic
structures of the oriented fibers are then stabilized by the photopolymerization of
methacryloyl moieties of the gelator. Upon heating above isotropization temperature
and then cooling to the room temperature, the LC is aligned along the groove
structures of the polymerized fibers. In display devices, the gel layers are employed
to amplify the low-tilting angles on the rubbed surfaces. In order to preserve the
amplified orientation, RMs in the gel are required.
Light transmission of the LC gels depends on the initial orientation and dielectric
anisotropy of LC. The uniaxially planar gels with a positive anisotropic LC or the
homeotropically aligned gels with a negative anisotropic LC may scatter the light
when an electric field is applied. The hydrogen-bonded molecules are preferentially
used as a LC gelator for the light scattering. As the temperature from I state
decreases, the fully dissolved gelator undergoes the micro-phase separation
from the LC media, and then the continuously self-assembled fiber networks are
formed. The finely dispersed fiber networks within the LC divide the LC molecules
into the small domains. Without applying an electric field, the LC cells completely
block the behind image because of the highly scattering states. As the voltage is
applied, the LC molecules are aligned perpendicular to the substrate plane, and
110
D.-Y. Kim et al.