Ferroelectric Liquid Crystal Film Research Articles

Linear defects forming the ground state of polar free standing smectic-C* films.

In this paper we report on observations of unusual linear defects forming spontaneously in polar free-standing smectic-C* films near the temperatures of thinning transitions. At high temperature a periodic structure of defects becomes the ground state of the system. We found that the defects are characterized by continuous rotation of the molecular orientation with a change of the sense of the rotation across the defects. We develop a simple theoretical model that describes the observed behavior. The structure of the defects is governed by the competition between two-dimensional quadratic and linear orientational elasticity. The proposed model explains the origin of the linear defects, the periodic structure and their transformation with temperature and chirality of the liquid crystal.

3a08 有機デバイスへの応用を目指した軸性強誘電性カラムナー液晶薄膜の作製及び表面観察(ソフトマター,口頭発表,2013年日本液晶学会討論会)

3a08 有機デバイスへの応用を目指した軸性強誘電性カラムナー液晶薄膜の作製及び表面観察(ソフトマター,口頭発表,2013年日本液晶学会討論会)

Self assembling effects of nano-particles in mesomorphic LB films

abstractLangmuir–Blodgett (LB) films of ferroelectric liquid crystal (FLC) doped with low concentration of functionalized nano-particles were prepared and characterised. Technique provides uniqueness for controlling molecular architecture through self-assembling. Pressure–area isotherms indicate nano-particles as well as FLC composite systems have capability to from stable monolayer. The molecular interaction between nano-particles and FLC molecules get increased during barrier compression. We observed various phase changes with doping of nano-particles in the FLC matrix. X-Ray diffraction confirmed that FLC retains its SmC* structure at low concentration doping of nano-particles. AFM images indicate that composites are deposited without disturbing translation behaviour FLC.

Effects of nanoparticle doping on the phase transitional behaviour of ferroelectric liquid crystal Langmuir–Blodgett composite films

Langmuir–Blodgett films of ferroelectric liquid crystals (FLCs) doped with a low concentration of functionalized Al: ZnO (AZO) nanoparticles were prepared and characterized. Pressure–area isotherms show that the nanoparticles as well as FLC composite systems have the capability to form stable monolayers at the air–water interface. The molecular interaction between nanoparticles and FLC molecules increased during barrier compression, which resulted in increased surface pressure. We observed various phases in isotherms with increasing concentration of nanoparticles in the FLC matrix. An X-ray diffraction profile at a low angle confirmed that FLCs retain their layer structure at a low concentration doping of AZO nanoparticles in the FLC matrix. Atomic force microscopy images indicate that low wt% composites are uniformly deposited without disturbing the translation behaviour of SmC* liquid crystals.

Influence of single-wall carbon nanotubes on Langmuir–Blodgett films of ferroelectric liquid crystals as studied by atomic force microscopy

Langmuir–Blodgett films of ferroelectric liquid crystal (LC) doped with low concentration of single-wall carbon nanotubes have been prepared and characterised. Pressure–area isotherms show that the films are stable and have good spreading properties. The interaction between nanotubes and LC molecules in the monolayer was increased during barrier compression, resulting in increased surface pressure. We observed phase change with increasing nanotube concentration in ferroelectric LC matrix. Atomic force microscopy profiles indicate uniform deposition of material on single crystal silicon wafer.

Mechanism of homeotropic alignment of ferroelectric liquid crystals doped with ferro-fluid and applications

We report homeotropic (HT) alignment of ferroelectric liquid crystal (FLC) doped with various concentrations of ferro-fluid (FF) without using any type of alignment layer. The FF induced HT alignment of FLC was found to be dependent on the doping concentration as revealed by optical micrographs, contact angle, and dielectric spectroscopy studies. Higher water contact angle of FF doped FLC films with respect to pure FLC film suggests higher surface energy of FF doped FLC than the surface energy of substrate. The physico-chemical mechanism together with steric model successfully explains the HT alignment of the studied FLC on the ITO substrate.

Effects of polymer viscosity on the polymerization switching and electro-optical properties of unaligned liquid crystal/UV curable polymer composites

Polymer dispersed ferroelectric liquid crystal composite films consisting of varying polymer viscosities were prepared by polymerization induced phase separation (PIPS) technique. It was found that polymer viscosity influences the polarization switching and optical responses. A polymer dispersed ferroelectric liquid crystal film of low polymer viscosity shows faster switching, however a higher optical transmission at ~ 70% was observed in a higher polymer viscosity film.

Probing the Electric-Field Modulated Ferroelectric Liquid Crystal Films with Phase-Sensitive Raman Imaging Technique

The electric-field-induced modulation of surface stabilized ferroelectric liquid crystal (SSFLC) films was in- vestigated with a phase sensitive Raman imaging. We found the technique not only effectively suppresses the nonresonant background of a Raman spectrum, but also yields an insight into the modulated amplitudes and phases of Raman peaks. By using the technique, the electro-optical switching SSFLC film doped with ZnO nanocrystals (nc-ZnO) was shown to switch in a more organized way and be less sensitive to the modulation induced disordering than an undoped SSFLC film. The method can be implemented in a conventional Raman spectroscopy to allow researchers probing into the spatial dis- tribution and modulation dynamics of electro-optic active species in a complex thin film.

Measurement of electro-optical parameters of a high contrast FLC film

We have fabricated a ferroelectric liquid crystal (FLC) film by using a novel ferroelectric mixture. The various ferroelectric parameters such as response time, spontaneous polarization and contrast ratio of the FLC film have been measured. Experimental results show that the FLC film exhibits high contrast ratios and fast optical response. The FLC film has a possibility of the use in display applications because of the performance characteristics.

What's new in digital displays?

Flexible displays using plastic film substrates are key devices for ubiquitous and universal services of digital broadcasting because of their mobile characteristics, low-cost productivity, and flexibility of viewing style. Polymer organic light-emitting devices (POLEDs) and ferroelectric liquid crystal (FLC) films composed of FLCs and polymer networks are promising display devices and materials for the reproduction of TV images in which gray-scale and high-speed response characteristics are required. Both prototype flexible displays of POLED and A4-sized FLC have been fabricated using phosphorescence materials. Performances of these displays showed substantial potential for ubiquitous and universal digital broadcasting services.

Measurement of Mechanical Resonance in Freely Suspended Ferroelectric Liquid Crystal Film

Mechanical vibration distributions of freely suspended ferroelectric liquid crystal films with various thicknesses in the range from 15 nm to 12 µm induced by applying a sinusoidal electric field are observed using a laser Doppler vibrometer. Mechanical resonance profiles of the freely suspended film are represented in the form of mechanical vibration distributions. Resonance frequency increases with the number of mechanical resonance modes. Surface tension is calculated from the number of mechanical resonance modes and the resonance frequency. The surface tension is not constant and is proportional to the thickness of the freely suspended film below 1.2 µm.

Dynamics of the molecular orientation field coupled to ions in two-dimensional ferroelectric liquid crystals

Molecular orientation fluctuations in ferroelectric smectic liquid crystals produce space charges, due to the divergence of the spontaneous polarization. These space charges interact with mobile ions, so that one must consider the coupled dynamics of the orientation and ionic degrees of freedom. Previous theory and light scattering experiments on thin free-standing films of ferroelectric liquid crystals have not included this coupling, possibly invalidating their quantitative conclusions. We consider the most important case of very slow ionic dynamics, compared to rapid orientational fluctuations, and focus on the use of a short electric field pulse to quench orientational fluctuations. We find that the resulting change in scattered light intensity must include a term due to the quasistatic ionic configuration, which has previously been ignored. In addition to developing the general theory, we present a simple model to demonstrate the role of this added term.

Role of electrostatics in the texture of islands in free-standing ferroelectric liquid crystal films

Curved textures of ferroelectric smectic-C* liquid crystals produce space charge when they involve divergence of the spontaneous polarization field. Impurity ions can partially screen this space charge, reducing long-range interactions to local ones. Through studies of the textures of islands on very thin free-standing smectic films, we see evidence of this effect, in which materials with a large spontaneous polarization have static structures described by a large effective bend elastic constant. To address this issue, we calculated the electrostatic free energy of a free-standing film of ferroelectric liquid crystal, showing how the screened Coulomb interaction contributes a term to the effective bend elastic constant, in the static long-wavelength limit. We report experiments which support the main features of this model.

Phase Modulation of Light by a Composite Film with Fine Ferroelectric Liquid Crystal Droplets: Theoretical Treatment

To describe phase and intensity modulation of the plane wave transmitted through a polymer dispersed ferroelectric liquid crystal (PDFLC) film with nanosized liquid crystal (LC) droplets the model based on the Foldy-Twersky and anisotropic dipole approximations is proposed. The dependence of phase shift and transmittance of films with fine droplets on their properties has been elucidated. The films with polarization-independent phase shift at switching of cylindrically symmetric structure of bistable smectic LC droplet director are investigated.

Measurement of Electrically Induced Vibration Profile in Freely Suspended Film of Ferroelectric Liquid Crystal

A mechanical vibration profile of a freely suspended film of a ferroelectric liquid crystal induced by applying a sinusoidal electric field is observed using a laser Doppler vibrometer. Mechanical resonance profiles of the freely suspended diaphragm are represented in the form of mechanical vibration distributions. The number of modes in the mechanical vibration increases with frequency. The peak displacement decreases with frequency and the magnitude is of the order of 0.8 µm under the application of 100 V/mm. The vibration displacement is proportional to the electric field applied to the liquid crystal diaphragm existing between two parallel electrodes. The observed mechanical displacements are due to the resonance of the freely suspended diaphragm, which is essential for the construction of a membrane device in relation to light beam reflection.

Self-Restoration by Smectic Layer Structures of Monostable Ferroelectric Liquid Crystal in Flexible Devices

In this paper, we discuss a self-restoration phenomenon affecting smectic layer deformation and molecular alignment in monostable ferroelectric liquid crystals used for flexible displays. First, the mechanical stability of tilted `bookshelf' structures of smectic layers anchored on substrates using alignment layers was examined by precisely shearing two substrates. The microscopic texture of a monostable ferroelectric liquid crystal showed tolerance to shearing and the self-restoration was thought to be due to a smectic layer reconnection phenomenon, whereas a conventional bistable ferroelectric liquid crystal film generated alignment defects due to the tilting of the stable molecular direction. We then fabricated a flexible monostable device containing fine polymer fiber networks, where anchoring of molecularly aligned polymer fibers led to the observation of monostable liquid crystal switching. A uniform liquid crystal alignment was maintained in a 100 mm×100 mm device even after bending more than 10000 times at a minimum radius of curvature of 20 mm, due to the enhanced shearing tolerance of the smectic layer structure.

Grating Based on Polymer-Stabilized Ferroelectric Liquid Crystal Films

A surface-stabilized ferroelectric liquid crystal (SSFLC) film, doped with a small amount of monomer, BAB-6, was fabricated. The alignment performance and electrooptical effect of SSFLC films polymerized under different polarities of the DC field were examined. A grating was then fabricated by curing a doped SSFLC cell with UV through a photomask. The grating thus formed was found to be a combination of a phase grating and an amplitude grating, between which the grating could be switched by applying a suitable voltage. The response time was in the order of 500–600 µs.

Influence of vapors of volatile organic compounds on spectral shift of bending vibrations of freely suspended ferroelectric liquid-crystal films

The influence of the vapors of volatile inert fluorocarbon compounds on the mechanical properties of freely suspended ferroelectric liquid-crystal films has been studied. It was shown that spectral shift of bending vibrations of freely suspended films depends on the mass variations of the associated ambient gas as well as on the adsorption of the vapors of volatile fluorocarbon compounds onto the film surface. It was also shown that adsorption layers similar to surfactants decrease the film surface tension by 11%–35% (4–12.5 dyn/cm).

HOLOGRAPHIC GRATING BASED ON DYE-DOPED SURFACE-STABLIZED FERROELECTRIC LIQUID CRYSTAL FILMS

A surface stabilized ferroelectric liquid crystal (SSFLC) film, doped with an azo dye, methyl red (MR), is fabricated. A holographic grating is written in this film, using two coherent Ar+ laser beams. Such a grating is formed by the re-orientation of the liquid crystal molecules caused by interaction with the photo-induced adsorption of the doped azo dyes. Experimental results show that the formed grating is permanent but electrically switchable, with a field of ~0.08 V/μm.

PA17 フォトクロミック色素を添加した強誘電性液晶自己保持膜の電界誘起振動特性(物理・物性)

PA17 フォトクロミック色素を添加した強誘電性液晶自己保持膜の電界誘起振動特性(物理・物性)