PHOTOTUNABLE SELECTIVE REFLECTION OF CHOLESTERIC LIQUID CRYSTALS

The dependence of the helical pitch of a cholesteric liquid crystal based on a composite photosensitive chiral dopant (cChD) on the intensity of light irradiation was studied. The transmission spectra and the selective reflection spectra of cholesteric liquid crystal cells were measured. The concentration of the cChD additive is calculated, so that the peak of selective reflection and its rearrangement occurs in the visible range of the electromagnetic radiation spectrum (380-780 nm). The possibility of photo-control by shifting the peak of the selective reflection of the cChD additive was studied, when exposed to LEDs with wavelengths of 365 nm and 450 nm, while reducing or increasing the intensity, a change in the spiral pitch was observed. Depending on the light intensity, part of the molecules of the chiral additive containing the azo group underwent isomerization, i.e. molecules in the trans-form passed to the cis-form, which led to a spectral shift of the selective reflection peak. If a small intensity of the 365 nm LED was applied, then some of the molecules were forced to transition from the trans- to the cis-form, and then, when illuminated with a 450 nm LED, from the cisto the trans-form. After reversible rearrangement, the properties of cholesteric liquid crystal changes due to interaction with light, because under the influence of light, the equilibrium ratio of the trans- and cis-isomers of the molecules of the substance changed, which macroscopically changed the torsion force of the chiral additive. Using two LEDs of 365 nm and 450 nm with different emission spectra, a reversible control of the cChD selective reflection peak in the visible range was obtained. The maximum displacement occurred at approximately 145 nm.The dependence of the helical pitch of a cholesteric liquid crystal based on a composite photosensitive chiral dopant (cChD) on the intensity of light irradiation was studied. The transmission spectra and the selective reflection spectra of cholesteric liquid crystal cells were measured. The concentration of the cChD additive is calculated, so that the peak of selective reflection and its rearrangement occurs in the visible range of the electromagnetic radiation spectrum (380-780 nm). The possibility of photo-control by shifting the peak of the selective reflection of the cChD additive was studied, when exposed to LEDs with wavelengths of 365 nm and 450 nm, while reducing or increasing the intensity, a change in the spiral pitch was observed. Depending on the light intensity, part of the molecules of the chiral additive containing the azo group underwent isomerization, i.e. molecules in the trans-form passed to the cis-form, which led to a spectral shift of the selective reflection peak. If a small intensity of the 365 nm LED was applied, then some of the molecules were forced to transition from the trans- to the cis-form, and then, when illuminated with a 450 nm LED, from the cisto the trans-form. After reversible rearrangement, the properties of cholesteric liquid crystal changes due to interaction with light, because under the influence of light, the equilibrium ratio of the trans- and cis-isomers of the molecules of the substance changed, which macroscopically changed the torsion force of the chiral additive. Using two LEDs of 365 nm and 450 nm with different emission spectra, a reversible control of the cChD selective reflection peak in the visible range was obtained. The maximum displacement occurred at approximately 145 nm

Phototunable selective reflection of cholesteric liquid crystals

The dependence of the helical pitch of a cholesteric liquid crystal based on a composite photosensitive chiral dopant (cChD) on the intensity of light irradiation was studied. The transmission spectra and the selective reflection spectra of cholesteric liquid crystal cells were measured. The concentration of the cChD additive is calculated, so that the peak of selective reflection and its rearrangement occurs in the visible range of the electromagnetic radiation spectrum (380-780 nm). The possibility of photo-control by shifting the peak of the selective reflection of the cChD additive was studied, when exposed to LEDs with wavelengths of 365 nm and 450 nm, while reducing or increasing the intensity, a change in the spiral pitch was observed. Depending on the light intensity, part of the molecules of the chiral additive containing the azo group underwent isomerization, i.e. molecules in the trans-form passed to the cis-form, which led to a spectral shift of the selective reflection peak. If a small intensity of the 365 nm LED was applied, then some of the molecules were forced to transition from the trans- to the cis-form, and then, when illuminated with a 450 nm LED, from the cis-to the trans-form. After reversible rearrangement, the properties of cholesteric liquid crystal changes due to interaction with light, because under the influence of light, the equilibrium ratio of the trans- and cis-isomers of the molecules of the substance changed, which macroscopically changed the torsion force of the chiral additive. Using two LEDs of 365 nm and 450 nm with different emission spectra, a reversible control of the cChD selective reflection peak in the visible range was obtained. The maximum displacement occurred at approximately 145 nm

Photoaligned liquid-crystal lens with a single low-voltage electrode

The simple design of liquid-crystal lenses with single electrode and operation voltage below 5 V is highly desired. We offer a new type of photoaligned liquid-crystal lens, where the refractive gradient is created by voltage application due to the patterned twist angle gradient. In this paper, we present our calculations and experimental data

New dyes for guest-host mode

New guest-host dyes of red and purple colour suitable for fabrication of ultrathin film polarizer from polymerizable liquid crystals are developed. When the absorption spectrum of dye matches the photopic curve, samples with total film thickness below 50 μm show good visual contrast

Изучение зависимостей углов подвеса градиентных фоточувствительных полимерных материалов от дозы экспонирования

The optimum composition of material and its treatment conditions for tilt angle gradient formation required for creation of liquid crystal (LC) lens is determined. The distinctive feature of the material is the two-step process of alignment layer surface for variable tilt angle: standard rubbing step that defines the azimuthal direction of LC alignment, and the exposure step that forms pretilt angle profile of the alignment layer. The subject is a copolymer, characterized by the percentage of its components. We used antiparallel LC cells to determine optimum сopolymer composition. The cells have alignment layers from polymer under investigation rubbed and exposed to different doses. It is established that before exposure materials have the property of vertical LC alignment, and after exposure planar LC alignment. Material without defects of both planar and vertical alignment suitable for LC lens application - VA-30 comprises 10% photosensitive styrene-based monomer; 30% methacrylate monomer, causing vertical LC alignment and 60% methacrylate monomer, causing planar LC alignment.Предметом исследования является тройной сополимер, отличающийся процентным содержанием его компонентов. Для определения оптимального состава сополимера изготовлены антипараллельные ЖК-ячейки с ориентирующими слоями, которые подвергались стандартной процедуре натирания и облучались при разных дозах. Установлено, что до облучения материалы вертикально ориентируют жидкий кристалл, а после облучения - планарно. Материал ВО-30, состоящий из светочувствительного блока 10%, полученного на основе стирола, метакрилатного мономера, вызывающего вертикальную ориентацию ЖК 30%, и метакрилатного мономера, вызывающего планарную ориентацию ЖК 60%, обладает бездефектной планарной и вертикальной ориентацией и может быть применим для создания ЖК-линзы

Photo-induced hole dipoles’ mechanism of liquid crystal photoalignment

We explain the observations and show the existence of the new photoalignment mechanism based on photo-induced dipole moments in azo-dye layer. Strong azimuthal anchoring energy >2x1 O'4 J/m2 is obtained within <0.5 J/cm2 exposure dose

Mass production of patterned polymerizable liquid crystal devices by roll-to-roll technology

Roll-to-Roll fabrication of patterned liquid crystal films and film-based devices is one of the most promising and anticipated LCD technology of today. The constraint of mass production is the suitable alignment process. The problem of high anchoring patterned liquid crystal alignment on plastic substrates has been challenged for over a decade. We solved it. The possibility of R2R fabrication of retarders with custom azimuthal angle, patterned retarders and vortex retarders is demonstrated

ГРАДИЕНТНЫЕ ОРИЕНТИРУЮЩИЕ МАТЕРИАЛЫ С РАЗНЫМ ПОРОГОМ ФОТОЧУВСТВИТЕЛЬНОСТИ ДЛЯ СОЗДАНИЯ УПРАВЛЯЕМЫХ ПОЛЯРИЗАЦИОННО-НЕЗАВИСИМЫХ ЖИДКОКРИСТАЛЛИЧЕСКИХ ЛИНЗ

The development of electrically tunable liquid crystal (LC) lenses is perspective and promising for a wide range of applications, for example, for imaging system, pico projectors, optical zoom systems, ophthalmology applications and other. Of particular note is the development of polarization-independent LC lenses, as eliminates polarizers from application devices that reduce the efficiency of light transmission through optical systems. Alignment benzaldehyde photosensitive materials, capable of changing the pretilt angles of nematic LC from 90 to 0 ºС in a controlled manner under UV exposure are developed. The anisotropy of the benzaldehyde alignment layers is generated by a two-stage treatment consisting of uniform rubbing with a cloth and subsequent non-polarized UV exposure. Inhomogeneous UV exposure of uniformly rubbed alignment layers allows formation of refractive index gradient inside the LC cell. The concept of tunable polarization-independent self-aligned LC lens based on gradient pretilt angle alignment materials with different photosensitivity is demonstrated. Self-alignment of two polarization-dependent sub-lens is achieved due to a single UV exposure act of two alignment layers, which are located on the same piece of glass on both sides, forming one common optical axis for a polarization-independent LC lens. The independence of the polarization of LC lenses is achieved by setting the azimuthal rubbing direction of the alignment layers of two polarizationdependent LC lenses perpendicular to each other. The sub-lens cells have uniform cell gap and are independently controlled using low-voltage driving. Devices based on gradient benzaldehyde alignment materials can be used in many modern optical and photonic devices.Разработка управляемых жидкокристаллических (ЖК) линз является перспективной и многообещающей для большого числа применений, например, для систем визуализации, пико- проекторов, систем оптического зума, офтальмологии, и др. Особого внимания заслуживает разработка поляризационно-независимых ЖК линз, так как позволяет исключить из прикладных устройств поляризаторы, которые снижают эффективность прохождения света сквозь оптические системы. Разработаны ориентирующие бензальдегидные фоточувствительные материалы, способные изменять углы преднаклона нематических жидких кристаллов от 90 до 0 º контролируемым образом под действием ультрафиолетового (УФ) экспонирующего излучения. Генерация анизотропии бензальдегидных ориентирующих слоев осуществлялась путем двухстадийной обработки, состоящей из однородного натирания тканью и последующего неполяризационного УФ экспонирования. Неоднородное УФ облучение однородно натертых тканью ориентирующих слоев позволяет сформировать градиент показателя преломления внутри ЖК ячейки. Продемонстрирован принцип изготовления управляемых поляризационно-независимых самосовмещенных ЖК линз на основе градиентных ориентирующих материалов с различным порогом фоточувствительности. Самосовмещение двух поляризационно-зависимых суб-линз обеспечивается благодаря простому единичному акту УФ экспонирования двух ориентирующих слоев, которые располагались по обе стороны одной стеклянной подложки, формируя общую оптическую ось поляризационно-независимых ЖК линз. Независимость от поляризации ЖК линз достигалась путем задания азимутального направления натирания ориентирующих слоев двух поляризационно-зависимых ЖК линз перпендикулярными друг другу. Ячейки суб-линз характеризовались однородным зазором, а их управление осуществлялось независимым образом с использованием низких управляющих напряжений. Устройства, изготавливаемые на основе градиентных бензальдегидных ориентирующих материалов, могут быть использованы в различных современных оптических и фотонных устройствах

Gradient pretilt angle alignment materials with different photosensitivity for tunable polarization-independent self-aligned LC lens

Alignment materials with different photosensitivity thresholds, capable of changing the pretilt angles from 90° to 0° under UV-B exposure have been developed. Inhomogeneous exposure of alignment layers allows formation of refractive index gradient inside the LC cell. The concept of polarization-independent self-aligned LC lens uniform cell gap and low-voltage driving is presented