205 research outputs found
Π€ΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΡ ΠΈ ΡΠΎΡΠΎΠΏΠ°ΡΡΠ΅ΡΠ½ΠΈΠ½Π³: ΠΠΎΠ²Π°Ρ ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠ°Ρ ΡΠ΅Ρ Π½ΠΎΠ»ΠΎΠ³ΠΈΡ Π΄Π»Ρ Π΄ΠΈΡΠΏΠ»Π΅Π΅Π² ΠΈ ΡΠΎΡΠΎΠ½ΠΈΠΊΠΈ
Objectives. Since the end of the 20th century, liquid crystals have taken a leading position as a working material for the display industry. In particular, this is due to the advances in the control of surface orientation in thin layers of liquid crystals, which is necessary for setting the initial orientation of the layer structure in the absence of an electric field. The operation of most liquid crystal displays is based on electro-optical effects, arising from the changes in the initial orientation of the layers when the electric field is turned on, and the relaxation of the orientation structure under the action of surfaces after the electric field is turned off. In this regard, the high quality of surface orientation directly affects the technical characteristics of liquid crystal displays. The traditional technology of rubbing substrates, currently used in the display industry, has several disadvantages associated with the formation of a static charge on the substrates and surface contamination with microparticles. This review discusses an alternative photoalignment technology for liquid crystals on the surface, using materials sensitive to polarization of electromagnetic irradiation. Also, this review describes various applications of photosensitive azo dyes as photo-oriented materials. Results. The alternative photoalignment technology, which employs materials sensitive to electromagnetic polarization, allows to create the orientation of liquid crystals on the surface without mechanical impact and to control the surface anchoring force of a liquid crystal. This provides the benefits of using the photoalignment technology in the display industry and photonicsβwhere the use of the rubbing technology is extremely difficult. The optical image rewriting mechanism is discussed, using electronic paper with photo-inert and photoaligned surfaces as an example. Further, different ways of using the photoalignment technology in liquid crystal photonics devices that control light beams are described. In particular, we consider switches, controllers and polarization rotators, optical attenuators, switchable diffraction gratings, polarization image analyzers, liquid crystal lenses, and ferroelectric liquid crystal displays with increased operation speed. Conclusions. The liquid crystal photoalignment and photopatterning technology is a promising tool for new display and photonics applications. It can be used for light polarization rotation; voltage controllable diffraction; fast switching of the liquid crystal refractive index; alignment of liquid crystals in super-thin photonic holes, curved and 3D surfaces; and many more applications.Π¦Π΅Π»ΠΈ. Π‘ ΠΊΠΎΠ½ΡΠ° XX Π²Π΅ΠΊΠ° ΠΆΠΈΠ΄ΠΊΠΈΠ΅ ΠΊΡΠΈΡΡΠ°Π»Π»Ρ Π·Π°Π½ΠΈΠΌΠ°ΡΡ Π»ΠΈΠ΄ΠΈΡΡΡΡΠ΅Π΅ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΠ΅ ΡΡΠ΅Π΄ΠΈ ΡΠ°Π±ΠΎΡΠΈΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ² Π΄Π»Ρ Π΄ΠΈΡΠΏΠ»Π΅ΠΉΠ½ΠΎΠΉ ΠΈΠ½Π΄ΡΡΡΡΠΈΠΈ. Π ΡΠ°ΡΡΠ½ΠΎΡΡΠΈ, ΡΡΠΎ ΡΡΠ°Π»ΠΎ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΡΠΌ Π±Π»Π°Π³ΠΎΠ΄Π°ΡΡ Π΄ΠΎΡΡΠΈΠΆΠ΅Π½ΠΈΡΠΌ Π² ΠΎΠ±Π»Π°ΡΡΠΈ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠ½ΠΎΠΉ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠ΅ΠΉ Π² ΡΠΎΠ½ΠΊΠΈΡ
ΡΠ»ΠΎΡΡ
ΠΆΠΈΠ΄ΠΊΠΈΡ
ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ², Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠΎΠΉ Π΄Π»Ρ Π·Π°Π΄Π°Π½ΠΈΡ ΠΈΡΡ
ΠΎΠ΄Π½ΠΎΠΉ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΡΡΡΠΊΡΡΡΡ ΡΠ»ΠΎΡ Π² ΠΎΡΡΡΡΡΡΠ²ΠΈΠ΅ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ. Π Π°Π±ΠΎΡΠ° Π±ΠΎΠ»ΡΡΠΈΠ½ΡΡΠ²Π° ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΈΡ
Π΄ΠΈΡΠΏΠ»Π΅Π΅Π² ΠΎΡΠ½ΠΎΠ²Π°Π½Π° Π½Π° ΡΠ»Π΅ΠΊΡΡΠΎΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΡΠ΅ΠΊΡΠ°Ρ
, Π²ΠΎΠ·Π½ΠΈΠΊΠ°ΡΡΠΈΡ
Π·Π° ΡΡΠ΅Ρ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΈΡΡ
ΠΎΠ΄Π½ΠΎΠΉ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ ΡΠ»ΠΎΠ΅Π² ΠΏΡΠΈ Π²ΠΊΠ»ΡΡΠ΅Π½ΠΈΠΈ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ ΠΈ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ΅Π»Π°ΠΊΡΠ°ΡΠΈΠΈ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΡΡΡΠΊΡΡΡΡ ΠΏΠΎΠ΄ Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ΠΌ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠ΅ΠΉ ΠΏΠΎΡΠ»Π΅ Π²ΡΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ. ΠΠΎ ΡΡΠΎΠΉ ΠΏΡΠΈΡΠΈΠ½Π΅ Π²ΡΡΠΎΠΊΠΎΠ΅ ΠΊΠ°ΡΠ΅ΡΡΠ²ΠΎ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠ½ΠΎΠΉ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ Π½Π°ΠΏΡΡΠΌΡΡ Π²Π»ΠΈΡΠ΅Ρ Π½Π° ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΈΠ΅ Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊΠΈ ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΈΡ
Π΄ΠΈΡΠΏΠ»Π΅Π΅Π². ΠΡΠΏΠΎΠ»ΡΠ·ΡΠ΅ΠΌΠ°Ρ Π² Π½Π°ΡΡΠΎΡΡΠ΅Π΅ Π²ΡΠ΅ΠΌΡ Π² Π΄ΠΈΡΠΏΠ»Π΅ΠΉΠ½ΠΎΠΉ ΠΈΠ½Π΄ΡΡΡΡΠΈΠΈ ΡΡΠ°Π΄ΠΈΡΠΈΠΎΠ½Π½Π°Ρ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ Π½Π°ΡΠΈΡΠ°Π½ΠΈΡ ΠΏΠΎΠ΄Π»ΠΎΠΆΠ΅ΠΊ ΠΈΠΌΠ΅Π΅Ρ ΡΡΠ΄ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΊΠΎΠ², ΡΠ²ΡΠ·Π°Π½Π½ΡΡ
Ρ ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ Π½Π° ΠΏΠΎΠ΄Π»ΠΎΠΆΠΊΠ°Ρ
ΡΡΠ°ΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π·Π°ΡΡΠ΄Π° ΠΈ Π·Π°Π³ΡΡΠ·Π½Π΅Π½ΠΈΠ΅ΠΌ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ ΠΌΠΈΠΊΡΠΎΡΠ°ΡΡΠΈΡΠ°ΠΌΠΈ. Π Π΄Π°Π½Π½ΠΎΠΌ ΠΎΠ±Π·ΠΎΡΠ΅ ΡΠ°ΡΡΠΌΠΎΡΡΠ΅Π½Π° Π°Π»ΡΡΠ΅ΡΠ½Π°ΡΠΈΠ²Π½Π°Ρ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ ΠΆΠΈΠ΄ΠΊΠΈΡ
ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² Π½Π° ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ², ΡΡΠ²ΡΡΠ²ΠΈΡΠ΅Π»ΡΠ½ΡΡ
ΠΊ ΠΏΠΎΠ»ΡΡΠΈΠ·Π°ΡΠΈΠΈ ΡΠ»Π΅ΠΊΡΡΠΎΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΈΠ·Π»ΡΡΠ΅Π½ΠΈΡ. Π’Π°ΠΊΠΆΠ΅ ΠΎΠΏΠΈΡΠ°Π½Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΡΠ΅ ΠΏΡΠΈΠ»ΠΎΠΆΠ΅Π½ΠΈΡ Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΡΠΎΡΠΎΡΡΠ²ΡΡΠ²ΠΈΡΠ΅Π»ΡΠ½ΡΡ
Π°Π·ΠΎΠΊΡΠ°ΡΠΈΡΠ΅Π»Π΅ΠΉ Π² ΠΊΠ°ΡΠ΅ΡΡΠ²Π΅ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠΈΡΡΠ΅ΠΌΡΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ². Π Π΅Π·ΡΠ»ΡΡΠ°ΡΡ. ΠΠ»ΡΡΠ΅ΡΠ½Π°ΡΠΈΠ²Π½Π°Ρ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΡΠΎΠ·Π΄Π°Π²Π°ΡΡ ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΡ ΠΆΠΈΠ΄ΠΊΠΈΡ
ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² Π½Π° ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ Π±Π΅Π· ΠΌΠ΅Ρ
Π°Π½ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΡ, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΊΠΎΠ½ΡΡΠΎΠ»ΠΈΡΠΎΠ²Π°ΡΡ ΡΠΈΠ»Ρ ΡΡΠ΅ΠΏΠ»Π΅Π½ΠΈΡ ΠΆΠΈΠ΄ΠΊΠΎΠ³ΠΎ ΠΊΡΠΈΡΡΠ°Π»Π»Π° Ρ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΡΡ ΠΏΠΎΠ΄Π»ΠΎΠΆΠ΅ΠΊ. ΠΡΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°Π΅Ρ ΠΏΡΠ΅ΠΈΠΌΡΡΠ΅ΡΡΠ²ΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ Π² Π΄ΠΈΡΠΏΠ»Π΅ΠΉΠ½ΠΎΠΉ ΠΈΠ½Π΄ΡΡΡΡΠΈΠΈ ΠΈ Π² ΡΠΎΡΠΎΠ½ΠΈΠΊΠ΅, Π³Π΄Π΅ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ Π½Π°ΡΠΈΡΠ°Π½ΠΈΡ ΠΊΡΠ°ΠΉΠ½Π΅ Π·Π°ΡΡΡΠ΄Π½ΠΈΡΠ΅Π»ΡΠ½ΠΎ. ΠΠ° ΠΏΡΠΈΠΌΠ΅ΡΠ΅ ΡΠ»Π΅ΠΊΡΡΠΎΠ½Π½ΠΎΠΉ Π±ΡΠΌΠ°Π³ΠΈ Ρ ΡΠΎΡΠΎΠΈΠ½Π΅ΡΡΠ½ΠΎΠΉ ΠΈ ΡΠΎΡΠΎΡΡΠ²ΡΡΠ²ΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΡΠΌΠΈ ΡΠ°ΡΡΠΌΠΎΡΡΠ΅Π½ ΠΌΠ΅Ρ
Π°Π½ΠΈΠ·ΠΌ ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠ΅ΡΠ΅Π·Π°ΠΏΠΈΡΠΈ ΠΈΠ·ΠΎΠ±ΡΠ°ΠΆΠ΅Π½ΠΈΡ. ΠΠΏΠΈΡΠ°Π½Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΡΠ΅ Π²Π°ΡΠΈΠ°Π½ΡΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΈ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ Π² ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΡΡΡΠΎΠΉΡΡΠ²Π°Ρ
ΡΠΎΡΠΎΠ½ΠΈΠΊΠΈ, ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡΠΈΡ
ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠ΅ ΡΠ²Π΅ΡΠΎΠ²ΡΠΌΠΈ ΠΏΡΡΠΊΠ°ΠΌΠΈ. Π ΡΠ°ΡΡΠ½ΠΎΡΡΠΈ, ΡΠ°ΡΡΠΌΠΎΡΡΠ΅Π½Ρ ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ°ΡΠ΅Π»ΠΈ, ΠΊΠΎΠ½ΡΡΠΎΠ»Π»Π΅ΡΡ ΠΈ Π²ΡΠ°ΡΠ°ΡΠ΅Π»ΠΈ ΠΏΠΎΠ»ΡΡΠΈΠ·Π°ΡΠΈΠΈ, ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π°ΡΡΠ΅Π½ΡΠ°ΡΠΎΡΡ, ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ°Π΅ΠΌΡΠ΅ Π΄ΠΈΡΡΠ°ΠΊΡΠΈΠΎΠ½Π½ΡΠ΅ ΡΠ΅ΡΠ΅ΡΠΊΠΈ, ΠΏΠΎΠ»ΡΡΠΈΠ·Π°ΡΠΈΠΎΠ½Π½ΡΠ΅ Π°Π½Π°Π»ΠΈΠ·Π°ΡΠΎΡΡ ΠΈΠ·ΠΎΠ±ΡΠ°ΠΆΠ΅Π½ΠΈΡ, ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π»ΠΈΠ½Π·Ρ, Π° ΡΠ°ΠΊΠΆΠ΅ ΡΠ΅ΡΡΠΎΡΠ»Π΅ΠΊΡΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΆΠΈΠ΄ΠΊΠΎΠΊΡΠΈΡΡΠ°Π»Π»ΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π΄ΠΈΡΠΏΠ»Π΅ΠΈ Ρ ΠΏΠΎΠ²ΡΡΠ΅Π½Π½ΡΠΌ Π±ΡΡΡΡΠΎΠ΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ΠΌ. ΠΡΠ²ΠΎΠ΄Ρ. Π’Π΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ ΡΠΎΡΠΎΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ ΠΈ ΡΠΎΡΠΎΠΏΠ°ΡΡΠ΅ΡΠ½ΠΈΠ½Π³Π° ΠΆΠΈΠ΄ΠΊΠΈΡ
ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² ΡΠ²Π»ΡΠ΅ΡΡΡ ΠΌΠ½ΠΎΠ³ΠΎΠΎΠ±Π΅ΡΠ°ΡΡΠ΅ΠΉ Π΄Π»Ρ Π½ΠΎΠ²ΡΡ
ΠΏΡΠΈΠ»ΠΎΠΆΠ΅Π½ΠΈΠΉ Π² ΠΎΠ±Π»Π°ΡΡΠΈ Π΄ΠΈΡΠΏΠ»Π΅Π΅Π² ΠΈ ΡΠΎΡΠΎΠ½ΠΈΠΊΠΈ. Π’Π΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡ ΠΌΠΎΠΆΠ΅Ρ Π±ΡΡΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½Π° Π΄Π»Ρ Π²ΡΠ°ΡΠ΅Π½ΠΈΡ ΠΏΠΎΠ»ΡΡΠΈΠ·Π°ΡΠΈΠΈ ΡΠ²Π΅ΡΠ°; Π΄ΠΈΡΡΠ°ΠΊΡΠΈΠΈ, ΡΠΏΡΠ°Π²Π»ΡΠ΅ΠΌΠΎΠΉ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΠ΅ΠΌ; Π±ΡΡΡΡΠΎΠ³ΠΎ ΠΏΠ΅ΡΠ΅ΠΊΠ»ΡΡΠ΅Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Ρ ΠΏΡΠ΅Π»ΠΎΠΌΠ»Π΅Π½ΠΈΡ ΠΆΠΈΠ΄ΠΊΠΎΠ³ΠΎ ΠΊΡΠΈΡΡΠ°Π»Π»Π°; ΠΎΡΠΈΠ΅Π½ΡΠ°ΡΠΈΠΈ ΠΆΠΈΠ΄ΠΊΠΈΡ
ΠΊΡΠΈΡΡΠ°Π»Π»ΠΎΠ² Π² ΡΡΠΏΠ΅ΡΡΠΎΠ½ΠΊΠΈΡ
ΡΠΎΡΠΎΠ½Π½ΡΡ
Π΄ΡΡΠ°Ρ
, Π½Π° ΠΈΡΠΊΡΠΈΠ²Π»Π΅Π½Π½ΡΡ
ΠΈ 3D ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΡΡ
; ΠΈ ΠΌΠ½ΠΎΠ³ΠΎΠ³ΠΎ Π΄ΡΡΠ³ΠΎΠ³ΠΎ.
Photoinduced ordering and anchoring properties of azo-dye films
We study both theoretically and experimentally anchoring properties of
photoaligning azo-dye films in contact with a nematic liquid crystal depending
on photoinduced ordering of azo-dye molecules. In the mean field approximation,
we found that the bare surface anchoring energy linearly depends on the azo-dye
order parameter and the azimuthal anchoring strength decays to zero in the
limit of vanishing photoinduced ordering. From the absorption dichroism spectra
measured in the azo-dye films that are prepared from the azo-dye derivative
with polymerizable terminal groups (SDA-2) we obtain dependence of the dichroic
ratio on the irradiation dose. We also measure the polar and azimuthal
anchoring strengths in nematic liquid crystal (NLC) cells aligned by the
azo-dye films and derive the anchoring strengths as functions of the dichroic
ratio. Though linear fitting of the experimental data for both anchoring
strengths gives reasonably well results, it, in contradiction with the theory,
predicts vanishing of the azimuthal anchoring strength at certain nonzero value
of the azo-dye order parameter. By using a simple phenomenological model we
show that this discrepancy can be attributed to the difference between the
surface and bulk order parameters in the films.Comment: revtex4, 25 pages, 9 figure
Kinetics of photoinduced ordering in azo-dye films: two-state and diffusion models
We study the kinetics of photoinduced ordering in the azo-dye SD1
photoaligning layers and present the results of modeling performed using two
different phenomenological approaches. A phenomenological two state model is
deduced from the master equation for an ensemble of two-level molecular
systems. Using an alternative approach, we formulate the two-dimensional (2D)
diffusion model as the free energy Fokker-Planck equation simplified for the
limiting regime of purely in-plane reorientation. The models are employed to
interpret the irradiation time dependence of the absorption order parameters
extracted from the available experimental data by using the exact solution to
the light transmission problem for a biaxially anisotropic absorbing layer. The
transient photoinduced structures are found to be biaxially anisotropic whereas
the photosteady and the initial states are uniaxial.Comment: revtex4, 34 pages, 9 figure
Carbon - containing covering for anchoring breaking nematic microdevices
We demonstrate experimentally, that inresidual atmosphere of scanning electron microscope the nano-scale carbon-containing (hydrocarbon) films by snuff effect can be produced. The micropattern of carbon film including axial-symmetric ones is defined by the e-beam rasteryesBelgorod State Universit
Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis
We experimentally study the reorientation dynamics of the nematic liquid
crystal easy axis at photoaligned azo-dye films under the combined action of
in-plane electric field and reorienting UV light linearly polarized at varying
polarization azimuth, . In contrast to the case where the light
polarization vector is parallel to the initial easy axis and , at
, the pronounced purely photoinduced reorientation is observed
outside the interelectrode gaps. In the regions between electrodes with
non-zero electric field, it is found that the dynamics of reorientation slows
down with and the sense of easy axis rotation is independent of the
sign of .Comment: revtex-4.1, 4 pages, 3 figure
Photoinduced reordering in thin azo-dye films and light-induced reorientation dynamics of nematic liquid-crystal easy axis
We theoretically study the kinetics of photoinduced reordering triggered by
linearly polarized (LP) reorienting light in thin azo-dye films that were
initially illuminated with LP ultraviolet (UV) pumping beam. The process of
reordering is treated as a rotational diffusion of molecules in the light
intensity-dependent mean-field potential. The two dimensional diffusion model
which is based on the free energy rotational Fokker-Planck equation and
describes the regime of in-plane reorientation is generalized to analyze the
dynamics of the azo-dye order parameter tensor at varying polarization azimuth
of the reorienting light. It is found that, in the photosteady state, the
intensity of LP reorienting light determines the scalar order parameter (the
largest eigenvalue of the order parameter tensor), whereas the steady state
orientation of the corresponding eigenvector (the in-plane principal axis)
depends solely on the polarization azimuth. We show that, under certain
conditions, reorientation takes place only if the reorienting light intensity
exceeds its critical value. Such threshold behavior is predicted to occur in
the bistability region provided that the initial principal axis lies in the
polarization plane of reorienting light. The model is used to interpret the
experimental data on the light-induced azimuthal gliding of liquid-crystal easy
axis on photoaligned azo-dye substrates.Comment: 27 pages, 11 fugure
Liquid crystal anchoring transitions on aligning substrates processed by plasma beam
We observe a sequence of the anchoring transitions in nematic liquid crystals
(NLC) sandwiched between the hydrophobic polyimide substrates treated with the
plasma beam. There is a pronounced continuous transition from homeotropic to
low tilted (nearly planar) alignment with the easy axis parallel to the
incidence plane of the plasma beam (the zenithal transition) that takes place
as the exposure dose increases. In NLC with positive dielectric anisotropy, a
further increase in the exposure dose results in in-plane reorientation of the
easy axis by 90 degrees (the azimuthal transition). This transition occurs
through the two-fold degenerated alignment characteristic for the second order
anchoring transitions. In contrast to critical behavior of anchoring, the
contact angle of NLC and water on the treated substrates monotonically declines
with the exposure dose. It follows that the surface concentration of
hydrophobic chains decreases continuously. The anchoring transitions under
consideration are qualitatively interpreted by using a simple phenomenological
model of competing easy axes which is studied by analyzing anchoring diagrams
of the generalized polar and non-polar anchoring models.Comment: revtex4, 18 pages, 10 figure
Orientational instabilities in nematics with weak anchoring under combined action of steady flow and external fields
We study the homogeneous and the spatially periodic instabilities in a
nematic liquid crystal layer subjected to steady plane {\em Couette} or {\em
Poiseuille} flow. The initial director orientation is perpendicular to the flow
plane. Weak anchoring at the confining plates and the influence of the external
{\em electric} and/or {\em magnetic} field are taken into account. Approximate
expressions for the critical shear rate are presented and compared with
semi-analytical solutions in case of Couette flow and numerical solutions of
the full set of nematodynamic equations for Poiseuille flow. In particular the
dependence of the type of instability and the threshold on the azimuthal and
the polar anchoring strength and external fields is analysed.Comment: 12 pages, 6 figure
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