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The study proposes a highly credible true random number generator based on the structural frustration of nematic liquid crystals, which refers to the appearance of two energetically equivalent structures in a nematic system. Frustration is induced in a simple liquid crystal cell by applying an electric field and observing optical textures under crossed polarizers. A clockwise or counterclockwise spiral image appears on 630 separate circular electrodes under the electric field, and random binary sequences are obtained by assigning a digit of 0 or 1 to each image. These sequences pass the strict statistical randomness tests of the National Institute of Standards and Technology with a pass rate of 0.992 or higher for the ten applicable tests and exhibit excellent uniformity. Furthermore, a simple method is introduced to convert the binary results to random decimal numbers with only a minimal amount of data processing. [ABSTRACT FROM AUTHOR]

As the diversity of information and data sources increases, anti-counterfeiting technologies become more critical in data recording, delivering goods and managing valuables. We propose a security device that can detect the denatured state or hacking of the information using liquid crystal's elastic and optical properties: Twist is allowed in the nematic phase, but not in the smectic phase. The optical polarisation varies in the twisted liquid crystal. The information images are engraved on the photo-alignment layer by irradiating polarised UV light in smectic phase. Several images are fabricated controlling polarisation directions. The engraved images are not visible as long as the smectic is maintained. To reveal the images, heating is necessary to nematic, where the twist is allowed. Even in nematic, we can selectively display or hide images by adjusting polariser angles. This security method can show a warning message or hide an image even if hacking occurs. Cooling back to the smectic phase distorts the image and it never returns to the initial phase. Therefore, if the texture is a distorted image, we notice an improper temperature change or product hacking. These devices are inexpensive, simple to manufacture, and effective in product security. [ABSTRACT FROM AUTHOR]

The anchoring strength of a nematic liquid crystal, 4-cyano-4'-pentylbiphenyl, is estimated on two-dimensional materials such as graphene, MoS2, and hBN. The changes in brightness attributed to the director rotation at the outer boundary or at the boundary of the orientation domains in the two-dimensional materials are optically observed. Anchoring energy coefficients in the polar and azimuthal directions are estimated by comparing the brightness profile between the experimental observations and numerical calculations. The azimuthal anchoring coefficient is larger than that of polar anchoring for all cases. The polar anchoring of graphite increases with the layer number within 10 layers. The anchoring of graphite is larger than that of MoS2 and hBN flakes. Although restricted results were obtained due to the limitations of the measurement, these results may give hints for understanding the interaction between liquid crystals and two-dimensional materials and can be used for applications. [ABSTRACT FROM AUTHOR]

This research proposes a general approach to determine the peculiarity of the interaction between colloidal particles in different liquid crystals. The main idea of this approach is in the definition of the colloidal particle as a source of the possible deformation of the ground state of the director field distribution. The ground state imposes restrictions on possible deformations and determines the peculiarity of the interaction between colloidal particles. Based on this approach, the Coulomb-like interaction between dipole particles in a cholesteric liquid crystal and a crucial change in the character of the interaction in a smectic liquid crystal are predicted. [ABSTRACT FROM AUTHOR]

A carbon fibre is a rod-like microstructure, the longitudinal axis of which is aligned with the orientation of the director in a nematic liquid crystal. A nematic liquid crystal with negative dielectric anisotropy is mixed with carbon fibres. By applying an electric field perpendicular to the director, the carbon fibres tend to rotate in response to the electric field, and the directors around the carbon fibres tends to suppress the rotation. We control individual carbon fibres to obtain an expected orientation by handling the competition of two actions. The carbon fibre barely reacts in a small electric field. Meanwhile, when the threshold electric field is exceeded, the carbon fibre rotates with a steep gradient in the direction of the electric field. The change in the rotation shows little hysteresis. As the length of the carbon fibre is increased, the threshold electric field decreases. We analysed the above process with a theoretical model considering the response of the carbon fibre and liquid crystal. This study shows the possibility of accurate analogue orientation control of individual rod-like microstructures. [ABSTRACT FROM AUTHOR]

Planarly aligned cholesteric liquid crystals of short pitch were applied by the in-plane electric field. The reorientation of the director, increasing pitch, and flexoelectricity induce the change of transmission. The main effect in this research is due to the director reorientation along the electric field. The flexoelectricity deters the change in the birefringence induced by the dielectric response. The response was very fast for the effectively thin periodic boundary of the half-pitch of liquid crystal. The contrast ratio was more than 80 for red light and the response time was less than 0.1 ms for the experimental conditions. [ABSTRACT FROM AUTHOR]

Presents information on a study which reported the measurements for the optical phase retardation of a polyimide-coated liquid crystal alignment layer that was rubbed at different temperatures. Experimental details; Results; Discussions.

Details a study on optical retardation measurements as a function of rubbing strength for both rubbed polyimide-coated substrates and cells containing the liquid crystal hexylcyanobiphenyl. Sample preparation; Optical retardation measurements; Discussion; Conclusions.

We construct quasi four-fold symmetric orientation patterns by irradiating laser light on a photoactive alignment layer. Double irradiations of spatially modulating interference light in orthogonal directions form symmetric patterns consisted of two stably and dominantly aligning liquid crystal (LC) domains. The LC texture continuously changes accompanying the switching, each state is definitely memorized, with changing electric field strength. A large number of quasistable but effectively stable states exist between two equivalently stable states. This will be suitable for next generation displays that will express full gray scale with multistability. [ABSTRACT FROM AUTHOR]

The alignment of liquid crystals is important in the manufacturing of devices. Usually, the alignment layer is prepared using a thin-film coating, thermal processing and processes such as rubbing or photo-alignment. Several trials without processes related to the alignment layer were performed for realizing vertical alignment. The main approaches were to utilize the self-assembly of the alignment agent on the substrate. Here, tiny amount of fumed silica, a kind of nano-particle, was added to nematic liquid crystals. With a low frequency electric field and thermal treatment, the region of vertical alignment was obtained. In addition, the efficiency of alignment was related to the polarity of the electric field. The vertical alignment by the fumed silica was active for negative polarity. This results in an easy and convenient way of obtaining vertical alignment. [ABSTRACT FROM AUTHOR]

Abstract: The effective rotational viscosity and polar anchoring coefficient of a nematic liquid crystal were determined using electro-optical response by changing the frequency of the electric field in the kilohertz range. Both quantities monotonically decreased with an increase in the frequency and converged to a certain value at several tens of kilohertz. The effective rotational viscosity changes more than the order of magnitude in experimental range. On the other hand, the effective value of anchoring coefficient changes several times. We tried to explain the trends with the effect of an electric field induced by the motion of ionic impurity in liquid crystal. [Copyright &y& Elsevier]

The anisotropy of the substrate is responsible for inducing alignment of liquid crystal. Several techniques such as mechanical contact, light and plasma irradiation, which can create the anisotropy, are being tried to apply in commercial products. In this research, electron beam irradiation was used to induce liquid crystal alignment. A tilted electron irradiation of around 1016/cm2 supposed to induce planar alignment in a lecithin-coated substrate. Polar anchoring was weakened by one order of magnitude, as compared to a rubbed PI layer, and the azimuthal anchoring was significantly weakened. An electron-beam-irradiated PI layer seemed not to induce the alignment. [ABSTRACT FROM AUTHOR]

It has long been appreciated that liquid-crystal (LC) devices in which the LC molecules adopt multiple stable orientations could drastically reduce the power consumption required for highinformation-content displays. But for the commonly used nematic LCs, which are intrinsically uniaxial in symmetry, no industrially feasible multi-stable LC device has been realized. Recently we demonstrated how bistability can be robustly engineered into a nematic LC device, by patterning a substrate with an orientational chequerboard pattern that enforces orthogonal LC alignment in neighbouring square domains. As a result of the four-fold symmetry of the pattern, the two diagonal axes of the chequerboard become equally stable macroscopic orientations. Here we extend this symmetry approach to obtain a tristable surface-aligned nematic LC. A microscopic pattern exhibiting six-fold symmetry is inscribed on a polyimide surface using the stylus of an atomic force microscope. The hexagonal symmetry of the microscopic orientational domains in turn gives rise to three stable macroscopic LC orientations, which are mutually switchable by an in-plane electric field. The resulting switching mode is surface driven, and hence should be compatible with demanding flexible display applications. [ABSTRACT FROM AUTHOR]

Colloidal particles dispersed in nematic liquid crystals are aligned along the orientation that minimizes the elastic free energy. Through applying an electric field to a nematic colloidal system, the orientation of the director can change. Consequently, colloidal particles realign to minimize the total free energy, which is the sum of the elastic and electric free energies. Herein, we demonstrate that if the preferred rotation directions given by the electric and elastic free energies are different during realignment, the rotation direction of the particle can be controlled by how we apply the electric field. When the strength of the electric field gradually increases, the particles rotate in the same direction as the rotation of the director. However, when a sufficiently high electric field is suddenly applied, the particles rotate in the opposite direction. In this study, we analyzed the effect of free energy on the bidirectional rotation behavior of the particles using a theoretical model. This study provides an effective approach to control the rotational behavior of colloidal particles over a wide-angle range between two orientational local minima. [ABSTRACT FROM AUTHOR]

The authors devised a technique for measuring the azimuthal anchoring coefficient of nematic liquid crystals. The coefficient was estimated calculating the varying ratio of magnetic coherence length to extrapolation length using light transmission to magnetic field. The paralleled control of the directors on the entrance surface, polarizer axis and magnetic field enables the transmission to sensitively reflect the anchoring. The extrapolation length was 0.48 μm for polyimide rubbed surface, 0.56 μm for rubbed poly-vinyl alcohol and 5.6 μm for photo-aligned polyimide. This technique has advantages such as insensitiveness to sample adjustment, covering wide range of anchoring and independence on the cell gap, electrodes and impurity. [ABSTRACT FROM AUTHOR]

An effective anchoring model for the patterned surface with bidirectional rubbing by atomic force microscope was proposed. The model was a simple additive function of two bidirectional anchoring contributions of the patterned surface, with consideration of higher-order terms of the anchoring function. The bistable switching behavior of the nematic liquid crystal cells with the patterned surface was investigated analytically and numerically using this anchoring model. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate a robust in-plane bistability of liquid-crystal surface alignment based on tailored submicrometer-sized surface domains imposing a frustrated alignment. By a nanorubbing technique utilizing the atomic force microscope, we prepared an orientational checkerboard pattern on polyimide layer, consisting of square unit domains on which the alignment is locally constrained to be planar yet orthogonal between the neighboring domains. Due to the four-fold rotational symmetry of the pattern, the two diagonal axes of the square domain become equally stable directions for the macroscopic liquid crystal alignment. The alignment could be switched between these two states by an in-plane electric field above a certain threshold, determined by the local azimuthal anchoring. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optical retardation measurements were performed on rubbed polyimide-coated substrates used for liquid-crystal cells. Based on measurements with and without a refractive index matching fluid, the retardation component due to the rub-induced scratches was extracted, and found to dominate the total retardation at higher rubbing strengths. Additionally, atomic force microscope measurements were performed to examine the rub-induced surface topography. The retardation calculated from the topography measurements was found to be in agreement with the optical results.© 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The embedding of liquid crystal (LC) droplets into polymer matrices yields polymer-dispersed liquid crystals (PDLCs), which play an important role in the formation of mechanically resistant films for flexible photonic devices. Despite the fact that PDLCs respond to a variety of physical and chemical stimuli, LCs have had limited success in detecting environmental pollutants due to a lack of reactive functional groups in their structures. In this work, we execute the idea of integrating functionalized carbon nanotubes (f-CNTs) into PDLCs to accelerate the absorption of gas molecules at room temperature (RT). The proposed f-CNT-PDLC sensor device was prepared by depositing the composite mixture onto an interdigitated electrode substrate and carrying out phase separation under UV light exposure. Compared to the pure PDLC device, the proposed device exhibited a response of ~12.9 % and 1 % for 100 and 5 ppm of NO 2 gas, and a linear relationship was obtained with gas concentrations. Furthermore, this device displayed a good reproducibility over five cycles, exhibiting an excellent selectivity against other interfering gases, such as H 2 S, CO, H 2 , and NH 3. The boosted response was attributed to charge transport between the NO 2 gas molecules and the f-CNTs, which was detected by measuring the change in electrical resistance caused by the f-CNTs, in addition to the orientational phase modulation of the f-CNTs and the LCs within a droplet. Our experimental results revealed that the proposed f-CNT-doped PDLCs are promising candidates for sensing various physical and chemical stimuli. [Display omitted] • An f-CNT-doped PDLC sensor device was developed for NO 2 gas detection. • The f-CNT dopant significantly improved the sensing performance of the PDLC device. • A difference in the droplet configuration was identified with NO 2 gas molecules. • A fast and specific sensing response was achieved with proposed f-CNT-PDLC sensor. [ABSTRACT FROM AUTHOR]

Abstract: Several studies have focused on synthesizing large-size graphene with an uniform crystal structure. However, graphene synthesized thus far is generally grainy. Grain properties such as size, shape, and crystal orientation are the basis for improving quality. In this study, a nematic liquid crystal is used to observe the several structural properties of graphene synthesized by chemical vapor deposition on the copper foil at once. The liquid crystal texture indicates the grain boundaries, and the liquid crystal directors reveal the crystal orientations of the graphene. The graphene islands appear to have plural grains of different crystal orientations, and the orientation of every lobe in island is mapped. The crystal rotating angles between layers in multilayer graphene are determined. In addition, the fine repeating lines on the graphene are shown to consist of graphene wrinkles. The liquid crystal does not damage graphene, and the process is easy, fast, reliable and applicable to large size; thus, the liquid crystal can be widely applied to analyze the structure of large-size graphene. [Copyright &y& Elsevier]