Yu et al. fabricated a photoresponsive 2D microarray with a period of about 1 μm
using CLCP containing azobenzene groups by using the replica molding technique
(Fig. 20, Yan et al. 2012). The CLCP microarray showed switchable behavior on the
reflection spectra by alternate irradiation of UV and visible light, accompanying with
the deformation of the CLCP pillars. Because the trans-cis photoisomerization
results in the alignment change of LC molecules especially in the side surface region
of pillars, the pillars contract along the long axis while they undergo expansion along
the short axis, leading to the increase in the diameter of the pillars and variation in
reflection spectra of the CLCP microarray. This is the first time to use the CLCP to
fabricate the microarray with a period of about 1 μm and manipulate switchable
behavior on the reflection spectra of the LC polymer microarray by light.
Furthermore, Yu et al. prepared novel photo and thermal dual-responsive inverse
opal films based on CLCP (Fig. 21, Zhao et al. 2014). The inverse opal film showed
switchable behavior on the reflection spectra by alternate irradiation of UV and
visible light or temperature, owing to the change in the order of the holes. This
change in the periodic structure is ascribed to the contraction of CLCP induced
by the photochemical reactions of the azobenzene moieties or the thermal-induced
phase transition. The optical properties drastically decreased by thermal or photoinduced phase transitions of the CLCP. It is the first time that azobenzene-containing
CLCPs have been used to prepare inverse opal film and achieve repeatable
switching behavior on the reflection spectra of film by using light, which can be
manipulated conveniently and controlled in situ. The reflectivity changed to a greater
extent compared to the 2D CLCP photonic crystals.
Wiersma et al. used direct laser writing system to pattern the complex 3D structures with sub-micrometer resolution (Zeng et al. 2014, 2015a). Microrobots were
fabricated with the CLCPs acting as the main body of walkers (Zeng et al. 2015b).
The light-induced maximum stress of these systems was measured to be 260 Æ 2 kPa,
which was comparable to natural muscles (10–200 kPa). The legs of walkers had a
conical shape, which was chosen to reduce the surface contact area, while 45
tilt of
the leg created asymmetry adhesion necessary for walking (Fig. 22a and b). The
artificial creature automatically performed various locomotion highly depended on
the interactions with the environment. The microscopic walker finished random or
directional walking, rotating, or jumping when placed on surfaces with different
treating methods (Fig. 22c).
Summary
It is the elegant combination of self-organization of properties of LCs and mechanical performance of organic polymers that enables photoresponsive CLCPs to
directly convert light energy into mechanical work. Light is an ideal stimulus,
for it can be localized, selective, and nondamaging and allows for remote activation and delivery of energy to a system. Due to their photocontrollable properties
without any aid of other motors, gears, and wires, it is very convenient and
attractive to reduce the size of the photo-driven CLCP actuators for their potential
384
L. Qin et al.
using CLCP containing azobenzene groups by using the replica molding technique
(Fig. 20, Yan et al. 2012). The CLCP microarray showed switchable behavior on the
reflection spectra by alternate irradiation of UV and visible light, accompanying with
the deformation of the CLCP pillars. Because the trans-cis photoisomerization
results in the alignment change of LC molecules especially in the side surface region
of pillars, the pillars contract along the long axis while they undergo expansion along
the short axis, leading to the increase in the diameter of the pillars and variation in
reflection spectra of the CLCP microarray. This is the first time to use the CLCP to
fabricate the microarray with a period of about 1 μm and manipulate switchable
behavior on the reflection spectra of the LC polymer microarray by light.
Furthermore, Yu et al. prepared novel photo and thermal dual-responsive inverse
opal films based on CLCP (Fig. 21, Zhao et al. 2014). The inverse opal film showed
switchable behavior on the reflection spectra by alternate irradiation of UV and
visible light or temperature, owing to the change in the order of the holes. This
change in the periodic structure is ascribed to the contraction of CLCP induced
by the photochemical reactions of the azobenzene moieties or the thermal-induced
phase transition. The optical properties drastically decreased by thermal or photoinduced phase transitions of the CLCP. It is the first time that azobenzene-containing
CLCPs have been used to prepare inverse opal film and achieve repeatable
switching behavior on the reflection spectra of film by using light, which can be
manipulated conveniently and controlled in situ. The reflectivity changed to a greater
extent compared to the 2D CLCP photonic crystals.
Wiersma et al. used direct laser writing system to pattern the complex 3D structures with sub-micrometer resolution (Zeng et al. 2014, 2015a). Microrobots were
fabricated with the CLCPs acting as the main body of walkers (Zeng et al. 2015b).
The light-induced maximum stress of these systems was measured to be 260 Æ 2 kPa,
which was comparable to natural muscles (10–200 kPa). The legs of walkers had a
conical shape, which was chosen to reduce the surface contact area, while 45
tilt of
the leg created asymmetry adhesion necessary for walking (Fig. 22a and b). The
artificial creature automatically performed various locomotion highly depended on
the interactions with the environment. The microscopic walker finished random or
directional walking, rotating, or jumping when placed on surfaces with different
treating methods (Fig. 22c).
Summary
It is the elegant combination of self-organization of properties of LCs and mechanical performance of organic polymers that enables photoresponsive CLCPs to
directly convert light energy into mechanical work. Light is an ideal stimulus,
for it can be localized, selective, and nondamaging and allows for remote activation and delivery of energy to a system. Due to their photocontrollable properties
without any aid of other motors, gears, and wires, it is very convenient and
attractive to reduce the size of the photo-driven CLCP actuators for their potential
384
L. Qin et al.