5.1: Optically Rewritable Liquid-Crystal Technology: A New Green E-Paper Approach

Abstract Optical rewritable E-paper is a valuable contribution to the green technology, as E-paper replaces usual paper with the same quality of image. The light printable rewritable paper is based on liquid crystal photoalignment and is suitable for labels and plastic card displays, price labels, E-albums, Eadvertisements. Introduction The idea of the electronic paper (E-paper) is to store and display information generated by computer on a light weight thin flexible and robust, yielded a writing time of 60 s). The alignment induced on a nematic LC by a photoaligned polymer film with azo-dye side groups was investigated [9]. The orientation of the LC molecules was be manipulated in a reversible manner by irradiating the film with a polarized light. The reversibility of the photo-induced alignment may allow recording and erasing of information in a LC display. The works mentioned above We will consider (i) development of new highly sensitive ORW photoaligning materials and layers; (ii) implementation of ORW liquid crystal structures, that are very durable, cheap and ready for the flexible challenge, contact printing of the polymer spacers and lamination; (iii) investigations of regimes of operation to allow to use cheap and low power consuming high efficient light sources such as blue LED as an alternative exposure light source instead of expensive and high power consuming mercury lamps or lasers. Results and Discussion Structure of ORW e-paper and them optical properties was investigated in our previous papers. In order to "print" some image on ORW e-paper, linear polarized light should be used [13] We investigate the influence of the optically addressing conditions on the stability and the speed for the reorientation process and describe optimal configuration of the STN cells for it. Best results are shown by thick TN LC cells with the thickness close to the third Mauguin minimum. Such TN cell rotates polarization plane on the angle equal to the twist angle of this cell for any wave length (wave guiding regime). Disadvantage this type display is small information capacity and very low resolution for graphic type display. STN LC display has larger information capacity and can be used for produce graphical information but such type cell requires a special optimization of its effective birefringence to obtain the optimal condition for operation in a blue region (440±10 nm), where the LED writing and erasing is the most efficien

The mechanism of interlayer interaction in smectic LC bringing to formation of ferro- and antiferroelectric phases

Interlayer interaction in the ferroelectric and antiferroelectric smectic phases is developed taking into account the distribution of dipole moment in molecule of liquid crystal. A very important role is played by mutual dislocation of different fragments of molecules inside smectic layer and it plays the key role in dipole-dipole interaction between neighbouring layers. Tilt of molecules in the smectic layer is followed from the ordering of the dipole moments in one direction of one layer. Three ordered phases are found, first is synclinic, second is anticlinic and third is twisted structure. In twisted structure the angle between two layers is 90 degree

Surface and liquid crystal interlayer interactions : characterizations and applications

For investigation of the interaction between alignment layer and nematic liquid crystal a simple method for determination of liquid crystal polar anchoring energy by electrical measurements was proposed. This method is based on two-channel scheme for capacitance measurements. The proposed method allows investigating anchoring properties of both planar and vertical aligned LC materials. This method was used for investigation the polar anchoring properties of photoaligning material before and after illumination and for LC structures with a high pretilt angle. Other method is the optical method for the determination of LC polar anchoring energy based on measurement of the reflection from LC cell versus voltage was proposed. The “bulk” electrooptical response of LC cell is not involved here at all. Best conditions for measurement are realized in twist configuration of LC cell. Polar and azimuthal anchoring energy can be measured in one cell. For smectic liquid crystal was done theoretical investigation of the interlayer interaction in the ferroelectric and antiferroelectric smectic phases. This description is based on the distribution of dipole moment in molecule of liquid crystal and dislocation them inside smectic layer. Tilt of molecules in the smectic layer is followed from the ordering of the dipole moments in one direction of one layer. Three ordered phases are found, first is synclinic, second is anticlinic and third is twisted structure. In twisted structure the angle between two layers is 90 degree. Theoretical investigation of the ferroelectric liquid crystals and the effects interaction liquid crystal with surface was used for develop a stabilization system for interferometer based on Zeeman laser. Received result, accuracy 10-7 for measurement of the linear dimensions, is better then can give other analogical systems. Application of liquid crystal technology decrease size of interferometer, weight and price. Company “Lasertex” (Poland) uses this stabilization system in interferometers which they produce

New method for determination of liquid crystal polar anchoring energy from reflective measurement

Liquid crystal (LC) polar anchoring energy was measured directly by determination of LC pretilt angle on the alignment surface analyzing the light reflected from the test cell. The LC cells with the cell gap less than 5 mu m with homogeneous and twist configuration were used in measurements

New method for measuring polar anchoring energy of nematic liquid crystals

A new method for measuring a polar anchoring energy of nematic liquid crystals (LCs) is proposed. A variation of LC tilt angle on the surface with an applied electrical field was determined by a reflective method. The twisted LC cell configuration was selected to compensate a contribution of the induced birefringence in the reflective spectra. The electrical field controlled reflectance was used to analyse the potential form of the polar anchoring energy and to define the anchoring strength. The proposed method is applicable for 2-5 m thick LC cells. © 2009 Taylor & Francis

Real-time simulation software for electro-optical calculation of LC cells

New principal for LCD modeling is proposed. We developed a real-time simulation software based on fast algorithms for solving differential equation. Rapid calculation of LC structure allows the change of electrooptical response to be seen immediately after changing any parameters of liquid crystal or cell configuration. The software is useful for fitting the measured parameters related to LC materials and device and for device optimization. To demonstrate the power of this software, transmittance voltage dependences were simulated and relaxation time optimizations were carried out. Our rapid algorithm can be used for dynamic driving simulations and overdrive optimization as well

Determination of the polar anchoring energy by electrical measurement

We propose a simple method for determination of polar anchoring coefficient by electrical measurements. The basic idea of this method is a two-channel scheme for capacitance measurements. The first channel uses one cell with planar alignment LC, the second channel uses the cell with vertical alignment (VA). Such method gives a possibility to investigate anchoring properties of planar and vertical alignment materials. Measurements of two cells at one time give possibility to compensate all volume effects in LC cell and investigate only surface effects. The method can be used for the cells, which do not have uniform planar or VA orientation. We applied this method to investigate the polar anchoring properties of photoaligning material before and after illumination. © 2005 SID

Integrated liquid crystal waveguide in polarization maintaining regime

The novel photonic devices based on integrated polarization maintaining Liquid Crystal waveguides are expected to have high optical performance in large photonic wavelength range, whereas the complexity of the design and the cost of the device are equivalent to regular passive matrix LC displays being cost efficient and friendly for mass-production. The combination of voltage controlled anisotropic properties of LC materials, specially shaped electrodes, pre-calculated applied voltage levels, dielectric layers and patterned liquid crystal alignment course the bulk of LC material to form a gradient waveguide. The layout of such LC waveguides can be created and switched by low voltages inside the liquid crystal cell. Suitable LC configurations were studied and optimized by commercial software LCD Master2D, Shintech. The waveguide properties were analyzed by the method of lines