film of LC using new fluorine-containing polyimides. We have provided detailed
spectroscopy study to understand the possible mechanism behind the photoalignment effect for liquid crystal molecules.
Keywords
Liquid crystal · Photoalignment · Fluorine-containing polyimide · Charge
transfer complexes · Optical property · Molecular orbital calculation
Definition
LC alignment methods are very important for manufacturing LCDs. The alignment
film located outside the LC layer is crucial for LCDs, because it is necessary to
precisely control the movement of LC molecules. The photoalignment method in
which polyimide films are radiated with LPUV light is one of the most effective
non-rubbing processes. We have summarized new photoalignment polyimides that
are different from the existing photoalignment polymers such as azo- and coumarincontaining polymers. We theorized that charge transfer interaction between the
polymer segments strongly depended on the photoreaction caused by LPUV
irradiation.
Photoalignment of Liquid Crystal Molecules
LCDs are widely used in cell phones, computers, and televisions because of their
high definition image combined with thinness and low power consumption compared with previously used cathode-ray tube displays. Figure 1 shows a cross section
of an LCD. In general, LCDs consist of a light source, two pieces of a polarizing
filter, an LC cell, a color filter controlling the color of the picture, and an antireflection film or the like. The LC cell is composed of an LC and LC alignment film
located outside the LC layer so that the LC molecules can be oriented. The thickness
of the LC alignment film is approximately 100 nm. The thin alignment film is crucial
for LCDs, because it is necessary to precisely control the movement of LC molecules. In addition, a precise molecular design is required for the alignment film.
The function and principle of an LCD are shown in Fig. 2. The LCD consists of two
polarizing filters and LC molecules between two electrodes. The change in the optical
refractive index when the voltage is applied controls the switching (ON/OFF).
As is evident from Fig. 2, the LC alignment on the substrate is very important for
manufacturing LCDs. It is generally impossible to orient LC molecules on the surface
of a nontreated substrate. However, it is possible to orient them when a polymer film is
coated on the surface of the substrate and some surface treatment is applied.
Mechanical rubbing method has been extensively used in the alignment of LC
molecules. However, mechanical rubbing causes problems such as electrostatic
charge and dust accumulation (Cognard 1982). To solve these problems, the
494
S. Sato et al.
spectroscopy study to understand the possible mechanism behind the photoalignment effect for liquid crystal molecules.
Keywords
Liquid crystal · Photoalignment · Fluorine-containing polyimide · Charge
transfer complexes · Optical property · Molecular orbital calculation
Definition
LC alignment methods are very important for manufacturing LCDs. The alignment
film located outside the LC layer is crucial for LCDs, because it is necessary to
precisely control the movement of LC molecules. The photoalignment method in
which polyimide films are radiated with LPUV light is one of the most effective
non-rubbing processes. We have summarized new photoalignment polyimides that
are different from the existing photoalignment polymers such as azo- and coumarincontaining polymers. We theorized that charge transfer interaction between the
polymer segments strongly depended on the photoreaction caused by LPUV
irradiation.
Photoalignment of Liquid Crystal Molecules
LCDs are widely used in cell phones, computers, and televisions because of their
high definition image combined with thinness and low power consumption compared with previously used cathode-ray tube displays. Figure 1 shows a cross section
of an LCD. In general, LCDs consist of a light source, two pieces of a polarizing
filter, an LC cell, a color filter controlling the color of the picture, and an antireflection film or the like. The LC cell is composed of an LC and LC alignment film
located outside the LC layer so that the LC molecules can be oriented. The thickness
of the LC alignment film is approximately 100 nm. The thin alignment film is crucial
for LCDs, because it is necessary to precisely control the movement of LC molecules. In addition, a precise molecular design is required for the alignment film.
The function and principle of an LCD are shown in Fig. 2. The LCD consists of two
polarizing filters and LC molecules between two electrodes. The change in the optical
refractive index when the voltage is applied controls the switching (ON/OFF).
As is evident from Fig. 2, the LC alignment on the substrate is very important for
manufacturing LCDs. It is generally impossible to orient LC molecules on the surface
of a nontreated substrate. However, it is possible to orient them when a polymer film is
coated on the surface of the substrate and some surface treatment is applied.
Mechanical rubbing method has been extensively used in the alignment of LC
molecules. However, mechanical rubbing causes problems such as electrostatic
charge and dust accumulation (Cognard 1982). To solve these problems, the
494
S. Sato et al.