LC Physics

Poster Session
Tuesday, Feb. 14, 2017  16:10-18:10
Paper No.  2017-TUE-P0101-P001
Siang-Yi Hong
Surface stabilization effect based on chiral polymer-doped blue phase liquid crystals

We report a method to stabilize blue phase liquid crystals (BPLCs) by photo-polymerizing the doped chiral polymers at isotropic phase. Such a method is called “Surface-stabilized blue phase liquid crystals (SSBP-LCs)”. SSBP-LCs can simplify the conventional manufacturing process of extending the temperature range of BP-LCs because the temperature of BPLCs does not have to precisely control in the narrow range during photo-polymerization. Also, we compare the electro-optical properties of SSBP-LCs with those of conventional polymer-stabilized BPLCs [1], the results show that the response time, the operation voltage, and others, can be improved. Accordingly, we believe that such an approach can improve the development of BP-LCs in LC technology

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Paper No.  2017-TUE-P0101-P002
Yu-Lin Nian
Voltage conditions for the formation of the electrohydrodynamically induced uniformly lying helix structure

This study is aimed to clarify the optimal frequency regime for well-aligned ULH structure via the voltage-induced EHD effect. According to the complex dielectric and the tan δ spectra, three frequencies designated fL, fR, and fH can be acquired at a given temperature. These frequencies are meaningful to characterize transport behaviors of ion charges under the application of a probe ac electric field within distinct frequency regimes. Based on measurements of voltage- and frequency-dependent transmission spectra and observations of optical textures, it can be summarized that the frequency regime (fL,< f < fR), where electrical charges can apparently oscillate in the bulk of the cell with less ion-accumulation on the electrode surfaces, is adequate to obtain well-structured ULH due to the effective induction of the EHD flow by appreciable voltages. As a result, this work is helpful to obtain a more uniform ULH alignment so as to enhance the optical contrast of the proposed devices and promote their practical uses.

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Paper No.  2017-TUE-P0101-P003
Koki Imamura
Field-induced orientation of liquid crystal micro-particles in a dual-frequency liquid crystal host

Liquid crystal (LC) micro-particles can be fabricated by polymerizing pre-aligned pohotopolymerizable LC molecules in the LC state, and are functional materials possessing optical and dielectric anisotropy. When the particles are dispersed in nematic LC hosts, they spontaneously rotate to match their inner molecular alignment along the host alignment, because they possess an anchoring potential along their inner molecular alignment. Moreover, reversible orientation switching of particles is possible in LC hosts by an electric field, and the rotation angle of particles is determined so as to minimize the free energy of the system, which comprises the electrostatic energy generated by the dielectric anisotropy of the LC particles and the elastic energy generated by the director deformation of the host LC induced around the particles. Here we investigate orientation of LC micro-particles in a dual-frequency LC (DFLC) host. Rectangular parallelepiped micro-particles with inner molecular alignment along the long axis are fabricated via two-photon excited direct laser writing, and dispersed in a DFLC to be electrically driven by a voltage applied in the in-plane direction of the cell. Interestingly, it was found that the particle rotates either clockwise or anticlockwise to align the inner molecular alignment parallel or perpendicular to the applied field.

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Paper No.  2017-TUE-P0101-P004
Wen-Fa Cheng
Electrically switchable and stable light scattering modes by dynamic fingerprint chiral textures

Negative dielectric nematic liquid crystals (LCs) doped with two azobenzene materials provide electrically switchable and permanently stable scattering mode light modulators based on dynamic fingerprint chiral textures (DFCT) with inhomogeneously helical axes. These light modulators can be switched between transparent states and scattering states. This study is the first report on the advantages of the light scattering mode of DFCT, including low operating voltage, permanently stable transmission.

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Paper No.  2017-TUE-P0101-P005
Sheng-Kuang Wu
Observation of photo-induced dielectrophoresis in liquid crystal droplets

In recent years, manipulation of tiny particle which size ranges from nanometer to millimeter is an attractive and important topic for scientists. To achieve the manipulation of tiny particles, such as sorting, handling, transport, and trapping, a number of innovative methods, including electrophoresis and dielectrophoresis (DEP) [1], optical tweezers [2], magnetic tweezers [3,4], acoustic wave [5], and fluidics [6], has been developed. In this work, we report the observation of DEP in liquid crystal (LC) droplets on a photoconductive substrate. By illuminating the photoconductive polymer layer on a glass substrate with ultraviolet light and a binary mask, a non-uniform electric field distribution can be induced on the photoconductive substrate. The non-uniform electric field induces the dipoles in LC droplets and provides a static-electric force for transporting the LC droplets. The whole process is based on the principle of DEP and thus it is not necessary for the manipulation of LC droplets occurring with any extra electric field. Fig. 1 shows the dynamic and the corresponding of the polarizing microscope images of the DEP process for the LC droplets. This study provides a new route for developing DEP-based LC device being potentially applied on optics.

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Paper No.  2017-TUE-P0101-P006
Chia-Ming Chang
A large and bistable liquid crystal lens by integrating a polarization switch with a passively anisotropic focusing element

A bistable negative lens with a large aperture size (~10mm) by integrating a polarization switch of ferroelectric liquid crystals (FLCs) with a passively anisotropic focusing element is demonstrated. The proposed lens not only exhibits electrically tunable bistability but also fast response time of sub-milliseconds. The tunable lens power ranges rom 0 to -1.74 Diopters. The electro-optical properties and imaging performances are demonstrated. In our previous work, the bistable lens is designed for red light due to the chromaticity of FLC-wave retarders. In order to extend the range of operating wavelength, we design a FLC-wave retarder with a proper cell gap. According to the simulation, it is able to operate in visible range with the response time of 171 us. The impact of this study is to provide a solution of electrically bistable liquid crystal lenses for the applications of portable devices, wearable devices and colored ophthalmic lenses. The design of the FLC-wave retarder can also be applied to the wavelength control of low level light therapy.

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Paper No.  2017-TUE-P0101-P007
Bo-An Chen
Anchoring Energies and Ionic Behaviors of Vertically Aligned Liquid Crystal Cells with Dominant Ions from Polyimide-Alignment Films

In this paper, we have studied the ionic behaviors of a rubbed-polyimide(PI)-vertical-aligned (VA) cell whose ions were originated from both liquid crystal mixture and PI layers within the same VA cell. We have used a LCR meter to measure the capacitances of the VA cell and heterodyne interferometry[1] to measure the phase change versus voltage at 1 kHz and the phase change versus time by applying a mid-grayscale square-wave voltage at 0.1 Hz to the VA cell. The latter were converted into the ionic-charge densities (or voltages) versus time accumulated adjacent to the PI-to-LC interfaces contributed from PI- and LC-sides, respectively. We have observed that the measured interfacial ionic-charge densities versus time were dominated by the ions generated within PI-alignment layers rather than the LC mixture in the same VA cell. The measured data were fitted to analytic solutions[2,3] for the derivations of ionic physical parameters for liquid crystal mixture and PI-alignment layers, respectively. We have also measured anchoring energies of two such VA cells with same LC mixture but two different PI-alignment materials, and observed a substantial difference in anchoring energies between them.

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Paper No.  2017-TUE-P0101-P008
Lyotropic Liquid Crystal textures in free-standing films of various surfactant-solvent systems

A lyotropic liquid crystal is a mixture of a surfactant in an appropriate solvent at a specific concentration and temperature. After leaving for a while, lyotropic liquid crystal textures are formed from the mixture, and can be observed under a polarizing optical microscope (POM), Figure 1. Generally, the textures are observed sandwiched between two parallel glass plates i.e., a microscope slide and a cover glass. In this work, we employed Triton X-100, lecithin and commercial detergents as surfactants and water as a solvent to study their free-standing films compare to those sandwiched between glass plates. A hole (3 nm in diametre) in an acrylic slide (2.5 cm x 7.5 cm) was dropped with an aqueous surfactant mixture and the lyotropic textures were observed under a polarizing optical microscope, Figure 2. The results showed that for Triton X-100 in water, the surfactant molecules which formed hexagonal columns aligned randomly between two glass plates. On the other hand, due to an interaction with the surface of the free standing film, the columns tried to lie down along the radius of the film, thus forming twisting textures.

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Paper No.  2017-TUE-P0101-P009
Bo-An Chen
Measurements of Residual Direct Current Voltage in Liquid Crystal Cells with Ionic Properties Dominated by Polyimide-Alignment Films

Prior publications on the measurements and interpretations of residual direct current (RDC) voltages in polyimide(PI)-film-aligned LC cells have been based on assumption that ions existed only in the LC medium but not in the PI-films. The RDC voltages were caused by the LC-to-PI-interfacial trapped ions originated only from the LC side. Based on the above assumption, Masanobu Mizusaki et al.[1] published a paper on generation mechanism of RDC voltage in a liquid crystal display and its evaluation parameters related to liquid crystal and alignment-layer materials. In this paper, for the first time, we report the measurements of RDC voltage in LC cells with ionic properties dominated by PI-alignment films [2] such that there are more ions driven to the PI-to-LC interfaces from PI sides than from LC side. We will discuss the interpretations of our data in comparison to the results published by Masanobu Mizusaki et al.

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Paper No.  2017-TUE-P0101-P010
Yu-Lin Shen
Optically switchable and electrically tunable photonic bandgap structure with an azo-chiral-doped liquid crystal defect layer

We consider photo-induced trans–cis isomerization of a chiral-azobenzene dye and propose an azo-chiral-doped liquid crystal (ACDLC) enabling photoswitching among the planar-nematic (N), the fingerprint (FP) and the planar (P)-cholesteric (CLC) states. The N with unwound molecular orientation and the P-CLC with helical pitch of ~900 nm can readily be achieved by illuminating the ACDLC cell with ultraviolet (UV, λ = 365 nm) and green (λ = 532 nm) lights, respectively. Noticeably, because dye molecules tend to be oriented in the state with the lowest absorptivity for the incident light, it is found that a metastable FP state is realized during the photo-induced textural transition between the N and the P states (Fig. 1). Furthermore, the ACDLC is employed as a central defect layer of a 1D PC. Since the ACDLC in the N, FP, and the P states possesses effective refractive indices of ne, no, and (ne + no)/2, respectively, three photoswitchable sets of defect modes in the 1D-PC/ACDLC cell are realized according to the photoswitching mechanism of the ACDLC. As a result, the proposed PC/ACDLC hybrid structure is promising for developing a multifunctional photonic device with unique optically switchable and electrically tunable spectral properties of defect-mode peaks.

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Paper No.  2017-TUE-P0101-P011
I-Tsang Lee
Hysteresis-free responses and morphological properties of polymer-stabilized uniformly lying helix structure

By means of temperature-dependent dielectric spectroscopy and observations of optical textures, our results show that the PS-ULH structure with excellent uniformity and stability, as examined after cycles of temperature tests, can be obtained in the temperature range covering both the CLC and the SmA phases. While the ULH state is regarded as a uniaxial crystal in the CLC phase, the voltage-dependent transmission (VT) curve of the cell under crossed polarizers as shown in Fig. 1 exhibits hysteresis-free electro-optical responses, suggesting the ability of linear gray-levels. Noticeably, the switching time between the PS-ULH and the homeotropic states measured in the order of a submillisecond can be reduced by increasing the concentration of the monomer doped into the cell. In the present work, the response time of the cell can be promoted to ~10 ms when the monomer concentration is 7 wt%. Consequently, the proposed PS-ULH structure, with high contrast ratio, hysteresis-free responses and millisecond order response time, is potentially applicable for developments of electro-optical devices, such as phase modulators and displays. Other remarkable results including phase behaviors and improved electro-optical properties of the PSULH structure based on our proposed approach will be clarified accordingly.

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Paper No.  2017-TUE-P0101-P012
Beom-Kyu Lee
The motion of a micro-particle in non-uniform director field of nematic liquid crystal

We investigate motions of spherical micro-particle in non-uniform director fields. In this study, we mix a particle into nematic liquid crystal. The director alignment on the particle is homeotropic boundary condition. The particle has to induce dipole or quadrupolar configuration. The dipole configuration accompanies a hyperbolic hedgehog defect and the quardrupolar configuration is encircled by a Saturn-ring disclination ring around particle [1,2]. We construct a liquid crystal cell. One substrate is prepared to have striped alignment patterns. To make a pattern we use a photo-alignment technique [3]. At this system, boundaries of striped pattern induce a distortion of liquid crystal. When the single particle locates in a position of the alignment pattern, it shows various dynamic motions. There seems to be an interaction between distortion of liquid crystal and particle configuration. In this report, we would like to show the interaction and its results.

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Paper No.  2017-TUE-P0101-P013
Chia-Hua Yu
Formation of a stable uniformly lying helix structure for the development of a tristable cholesteric liquid crystal

Cholesteric liquid crystals (CLCs) with uniformly lying helix (ULH) structure are well-known for their superior electro-optical characteristics, including fast flexoelectric switching and tunable birefringence that are potentially for a variety of optoelectronic and photonic applications. Unfortunately, simple device geometry is unavailable to permit the ULH structure as a minimum energy state so that it has been proven difficultly in creating a defect-free ULH alignment. In considering the prospective developments, we propose an approach to the formation of a stable and switchable ULH structure. Here, CLC mixtures with distinct helical pitches were individually injected into 90-twisted cells. When sustaining the cell in the homeotropic state by an external voltage, turning off the voltage quickly and switching directly to a lowered voltage, result in the formation of planar and focal conic states, respectively. Noticeably, a stable ULH texture can be created by descending the voltage slowly to zero, due to the generation of twist deformation of LC molecules near the substrates during the nematic–CLC transition. Accordingly, by utilizing the aforementioned tristable-switching mechanism together with the feature of electrically controllable birefringence in the ULH state, the proposed CLC cell is potentially applicable as a tunable phase modulator and an energy-efficient photonic device.

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Paper No.  2017-TUE-P0101-P014
Zhi-Hong Jian
Development of an energy-efficient guest–host nematic device with a high-dielectric-anisotropy nematic host

The concept supporting the aforementioned results can be explained as follows. In a dye-doped LC cell, dye molecules follow the director of the LC host in that they are squeezed by and attached to the long axes of LC molecules. From the point of view of material design, the rod-like LC with larger refractive index as well as dielectric anisotropy typically reflects longer molecular conjugation and higher ordering. Accordingly, promoted CR and reduced operating voltages are expected in a guest–host LC device comprising a high- nematic host, presumably due to the enhancement in ordering of dye molecules. As a result, our work provides a promising pathway to a high contrast and energy-efficient guest–host device for the application in, say, smart windows.

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Paper No.  2017-TUE-P0101-P015
Shao-Ming Lu
Electrically switchable cholesteric liquid crystals with Bragg reflection and phase retardation

In this study, we explore a cholesteric liquid crystal device with a three-terminal electrode structure that can be switched between standing-helix (SH) and lying-helix (LH) molecular configurations by in-plane and vertical electrical field. The ITO interdigital electrode arrays with a width of 8𝜇m and separation of 12𝜇m are fabricated on the bottom glass substrate to produce in-plane electric field, and the uniform ITO thin film is deposited on the top glass substrate as the sheet electrode to create nonuniform vertical electric field. The ChLC cell with a three-terminal electrode structure exhibits interesting optical characteristics. Both Bragg reflection and phase retardation can be electrically switched.

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Paper No.  2017-TUE-P0101-P016
Dae Young Gwon
Liquid Crystal Director Field in a colloidal confinement

In this paper, we calculate liquid crystal director field in circularly confined capsules by using Q-tensor method, which can calculate not only the LC director field in bulk area but the local phase transition in high elastic distortion area. We calculated LC director filed in colloidal capsule with the boundary condition of both homogeneous state and homeotropic state.

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Paper No.  2017-TUE-P0101-P017
Wei-Jin Chang
Verification of nonlinear optical properties of diacrylate using Z-scan technique

Recently, two-photon absorption (TPA) in diacrylate mesogens, RM82 and RM257, was reported [1]. However, the authenticity that the TPA happened in the mesogens has been questioned. A major feature that distinguishes TPA from one-photon absorption is that TPA is, as being classified, a third-order nonlinear optical process at a wavelength λ [2]. Z-scan is a simple and highly sensitive single-beam experimental technique, and has been widely used to measure both nonlinear absorption and nonlinear refraction [3]. Recently, we employed Z-scan technique to verify the nonlinear optical property of diacrylate. In the present study, a 21 mW HeNe laser operated at wavelength 632.8nm was used to provide probe beam. Sample was mounted in a holder which was controlled to move along the laser beam. Data were acquired when the samples were at difference temperature. Marked response signals were observed from both diacrylate compounds RM82 and RM257, and indicate the existence of nonlinear optical process in the mesogens.

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Paper No.  2017-TUE-P0101-P018
Meng-Ju Pan
Electrically construable optical filters using silver nanoslits embedded with liquid crystals

Nanoscale plasmonic structures have attracted much attention owing to their strong absorption at visible-light regime [1-3]. The strong absorption arises from the collective oscillation of the electrons at the surfaces of nanoscale metal structures, and the wavelengths of their absorption peaks depend on the refractive indices of the media that surround the structures. As a result, the nanoscale plasmonic structures can be used to develop biomedical sensors [1-3]. This work fabricates an electrically construable optical filter using silver nanoslits embedded with liquid crystal. The intensity (wavelength) of the filter can be tuned at a low (high) voltage region between 1 (5) V and 3 (50) V due to the strong anchoring energy of the nanoslits, as presented in Fig. 1(a) [1(b)]. The optical filter, together with an LED, functions as a single-wavelength light source. Such a light source can be used to develop lab-on-chips for biomedical detection and photonic integrated circuits.

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Paper No.  2017-TUE-P0101-P019
Jia-Heng Dai
Thermal and optical studies of perovskite quantum dots doped cholesteric liquid crystal resonating cavity

We experimentally studied the thermal and optical properties of the laser lines and fluorescent spectrum generated by a thermally tunable cholesteric liquid crystal (CLC) laser. High-quality perovskite quantum dots with cubic structure were simply synthesized by a novel low temperature solvothermal pathway. Relationship between band edge effect and threshold energy has been investigated in optical emission using perovskite quantum dots embedded in the one dimensional photonic crystal device (CLC). Upon 532nm pulse laser excitation, amplified spontaneous emission (ASE) and optical gain were observed, for the first time, perovskite quantum dots doping cholesteric liquid crystal (PDCLC). This work demonstrates a thermally tunable perovskite quantum dots-doped cholesteric liquid crystal distributed feedback (DFB) laser or ASE. Such a tunable optical can be used in the fabrication of tunable optical sources and biosensors, and in integrated photonic circuits, optical communication, and displays.

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Paper No.  2017-TUE-P0101-P020
Jun-Yong Lee
Measuring the anchoring strength of homeotropic alignment using reflection in optical microscope

Compared to planar alignment, the homeotropic alignment is not ease to obtain the anchoring strength for large background signal. Here, the anchoring strength of the homeotropic alignment is obtained by measuring the reflected light from the liquid crystal cell in reflection mode of the optical microscope and modelling the cell response. We prepared a cell made of two substrates of homeotropic alignment. One substrate has the alignment layer we have interest in. The other has weak anchoring. The liquid crystal we used has a positive dielectric anisotropy in nematic phase and the electrodes are prepared to apply planar electric field. The depth of focus of the objective lens is selected to be less than the cell gap and light was focused on the interested substrate. With applying the electric field, the director near weak anchoring substrate responds rapidly. In contrast, the director near interested substrate responds slowly. The reflected light from the cell is mostly from the near the interface of interested substrate. The process of the director response is modelled and the change of reflection can be obtained for different anchoring strength. Finding appropriate anchoring strength, we obtain well fitted calculation result to the experiment.

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Paper No.  2017-TUE-P0101-P021
Yi-Ti Wen
Response of diacrylate mesogens to He-Ne laser interference field

Diacrylate, compounds RM257 and RM82 are liquid crystal reagents. They are light sensitivity and two-photon absorption activity can be polymerized when initiated by ultraviolet irradiation. In previous studies , their non-linear characteristics were reported and optical interference patterns can be produced in the compounds.In this study, we studied effects of optical irradiation on the diacrylate reagents using a two-beam interference field that was produced using a He-Ne laser with a power of 21 mW and a wavelength of 632.8 nm. Samples of the diacrylate reagents were irradiated at the position where the interference fringes formed. In additional, a three-beam interference pattern was also used in order to form a spatial periodic structure in the samples. In this report, discussions on the relevant observations are provided.

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Paper No.  2017-TUE-P0101-P022
Ting-Hui Chen
Diffraction-tuned circular symmetrical gratings with cholesteric liquid crystals

The diffraction-tuned circular gratings with the cholesteric liquid crystals (CLCs) have been investigated by using circular alignment method. The phase-grating like fingerprint texture of CLCs can be obtained by operating at the low voltage under a suitable d/p ratio (d/p ≤ 3) and two types of the fingerprint texture are defined with various range of d/p ratio [1,2]. Fingerprint texture with d/p ratio of 0.5~1.0 is the developable-modulation (DM) type and the stripes simultaneously appear across the whole sample. For the cell with d/p ratio of 1.5~3.0 is growing-modulation (GM) type and the stripes slowly extend to the whole sample along the rubbing direction from defects. In this study, the pitch of CLC sample fabricated with GM type can be easily tuned by varying voltage. The tuning maximum angle of second-order diffraction achieves 20.9 degrees with the CLC sample under the condition of d/p = 2.5. The circular gratings have the polarization-independent property because its stripe exhibits the circular symmetrical structure. According to above characteristics, the CLC circular gratings are polarization-insensitive and can be potentially applied in optical switching devices for widely tunable feature.

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Paper No.  2017-TUE-P0101-P023
Tian-Yi Jhuang
High-efficiency reflective display based on polymer-stabilized blue phase liquid crystals

A simple method of fabricating high-reflective display with the polymer-stabilized blue phase liquid crystals (PS-BPLCs) is proposed. The PS-BPLCs are formed from the polymer monomer-doped BPLCs curing by the UV light, resulting in the more stable structure and the wider temperature range of the BPLCs. The uniform reflective color and high Bragg's reflection of the BPLCs can be obtained by rubbing the surface of sample. In this work, three PS-BPLC samples are produced as the basic sub-pixels of the display, which can reflect the red (R), green (G), and blue (B) lights, respectively. The results show that the G- and B-sub-pixel of the PS-BPLC samples have a good behavior of photoelectric when applied voltage. The reflectances of three PS-BPLC samples (R, G, and B) are about 50, 77, and 60 %, respectively. Moreover, the major problem of PS-BPLCs with high operating voltage is expected to improve in the further study.

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Paper No.  2017-TUE-P0101-P024
Che-Wen Chiang
Entanglement-Free Determination of Pretilt Angles of Twisted Nematic Liquid-crystal Cells by Phase Measurement

For twisted nematic(TN) liquid crystal (LC) displays, the pretilt angle of the TN LC medium within the cell has a significant impact on display qualities such as viewing angles and response times as well as shifting the light leaking disclination lines into the black-matrix area within pixels of thin-film-transistor driven TN panel for high contrast ratio. In this paper, we have developed an optical method to determine TN pretilt angle free of entanglement with TN cell gap based on heterodyne measurements of phase versus incident angle of a thin TN cell subjected to out-of-plane rotations. We believe that our method of measuring phases has advantages of a simpler setup, better stability, higher signal-to-noise ratio, and less sensitive to ambient EMI than the conventional method of measuring intensity[1].

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Paper No.  2017-TUE-P0101-P025
Yu-Cheng Hsiao
On the phase sequence of a blue-phase liquid crystal

type of liquid-crystalline phases called the blue phases (BPs) was observed back in 1888. While BPIII is believed to be an amorphous network of disclination lines, BPII and BPI possess distinct three-dimensional cubic lattice structures induced by self-assembled double twist cylinders, exhibiting selective Bragg reflections in accordance with the cubic lattice. BPs appear in a temperature range between a chiral nematic phase and an isotropic phase, which has been recognized as a scientific fact. However, with technology advancing continually, an unusual phase sequence of BP liquid crystals (LCs) has been observed and some researchers termed a unique phase situated between the BP and isotropic phases as the sphere phase [1, 2]. Here, we show and elucidate the “corrected” phase sequence for BPs based on our experimental observations. The BP actually originates from a very narrow temperature range of a chiral phase near the isotropic phase in the cooling process. The random isotropic phase first transforms to a disclination-rich chiral phase, and then LC molecules become connected, pairing helices to produce a double twist cylinder. Finally a BP lattice grows.

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Paper No.  2017-TUE-P0101-P026
Ying-Hsiang Wang
TiO2 nanoparticles as an anti-UV agent for retaining device performance of nematic liquid crystals

Our experimental results of real-time measurements indicated that both the TiO2-doped and undoped LC cells exhibit promoted ion densities and reduced voltage holding ratios (VHRs) during the UV exposure. After turning off the UV light, the VHR of TiO2-doped LC cells can recover over time (in hours). For instance, we found that the VHR of TiO2-doped LC decreased from 71% to 43% by 2-mW/cm2 UV irradiation for 60 min but it was remarkably recovered to 61% in the UV-off condition for 180 min. The recovery of UV-degraded electrical properties over time in TiO2-doped LC cells is believed to be attributable to the regained ion-trapping ability of TiO2 NPs. For LC-based devices, cells exposed to the ultraviolet light often lead to the deterioration in electro-optical performance caused by the natural LC-material degradation and ion injection from the aligning materials. Accordingly, the proposed LC/TiO2 colloids can be regarded as a promising system for the use of outdoor LC devices characterized by regained excellence in electrical performance after UV exposure.

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Paper No.  2017-TUE-P0101-P027
Hung-I Wang
Optically induced electric dipole moment for the stabilization of ferroelectric liquid crystals

Surface-stabilized ferroelectric liquid crystal (SSFLC) possesses the advantages of ultra-fast response and bistability. However, the main key point is the extremely thin gap (usually < 2 m) of the LC cell, which is difficult to be fabricated. In this study, we found that the cell gap to achieve SSFLC can be increased if the dopant with high electric dipole moment is doped. Here, the employed dopant is an azobenzene material, whose electric dipole moment at cis-isomer is higher than that at trans-isomer. Briefly, the selected cell gap of the homogeneous alignment LC cell herein was about 5 m, and the material was azobenzene-doped FLC. Figure 1(a)-1(c) show the observations under cross-polarizer polarized optical microscope before being treated with UV illumination, as known as trans-isomers. Clearly, no bistability can be obtained. Moreover, after being treated with UV illumination, the trans-isomers having low electric dipole moment have been transferred to cis-isomers having high electric dipole moment so that the FLC can be stabilized at zero voltage application as shown in Figs. 1(d)-1(f) [1-3]. Reversely, by heating the FLC sample, the bistable characteristic of FLC can be removed.

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Paper No.  2017-TUE-P0101-P028
Kuanchanok Pienpanich
Mesomorphic properties of thermotropic liquid crystal free-standing films

Liquid crystals textures are the main implementation for liquid crystal phase classifications. By doing so, a mesogen is placed between two glass plates, i.e. a microscope glass slide and a cover slide, and the textures can be observed under a polarizing optical microscope (POM), with or without a temperature controller. According to this report, we dissolved 5CB in dichloromethane and the mixture was dropped a hole (2 nm in diameter) in a microscope slide (2.5 cm x 7.5 cm). The mixture was left to dry at room temperature for 2 hours, where the 5CB free standing film was developed in the hole. The textures of the film were observed under a polarizing optical microscope, Figure 2. On the other hand, 5CB was also observed under the microscope using the conventional method, Figure 1. It is concluded that 5CB molecules placed between two glass plates exhibited classical and colorful textures with some defects due to the birefringent properties of the compound. Contradictly, the textures of the free standing film were almost colorless with a defect point. The model of both textures, in sandwiched glass plates and in free standing film, will be presented and discussed in the presentation.

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Paper No.  2017-TUE-P0101-P029
Chi-Ting Horng
An organic photoconductive film applied in optically tunable focus of Fresnel lens

This study presents an optically tunable focal length of Fresnel lens with PVK/C60 layer and Sagnac interferometer. The PVK doped with C60 can enhance the absorbance in visible wavelength range. By using Sagnac interferometer with visible wavelength, a Fresnel-like pattern can be induced on the PVK/C60 layer which results in conductive and nonconductive structures corresponding to bright and dark regions. Thus, a Fresnel lens can be constructed through the mismatch of refractive index between adjacent zones with an external voltage. The focal length of the proposed Fresnel lens can be easily tuned by varying the size of the Sagnac pattern and the focusing efficiency can also be controlled optically.

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Paper No.  2017-TUE-P0101-P030
Yu-Tzu Yang
Morphology and topology of cholesteric liquid crystal microdroplets on electrospun polymeric fibers

The orientation of liquid crystals and the formation of topological defects of liquid crystals in confined geometries are determined by the nematic elasticity, chirality and surface anchoring [1-3]. Here we report the deformations of the inner orientation in cholesteric liquid crystal (CLC) microdroplets with short- and long-pitch deposited on polymeric fibers, as shown in Fig. 1. Two kinds of surface anchoring, perpendicular anchoring at the air-CLC droplet interface and planar anchoring at the fiber-CLC droplet interface, coexist in this system. We observed the equilibrium structures of the CLC microdroplets thermally cooled down from isotropic phase to chiral nematic phase. In addition to the thermal dependent deformations of the CLC microdroplets, this study also discusses the photo-dependent deformations of the azo-CLC microdroplets, which are composed of azo-LC-doped CLCs or azo-chiral-doped CLCs. The UV-irradiation induced trans to cis isomerization of the azo-materials can disturb the orientations of the LCs or the pitch of the CLCs inside the microdroplets and thus the disclinations, as shown in Fig. 2. The photo-controlled deformations of the CLC microdroplets on polymeric fibers presented in this work can be used to achieve topological remote control and open a route to develop devices based on topologically structured soft media.

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Paper No.  2017-TUE-P0101-P031
Byeong-Cheon Kim
Enhancement of the Helical Twisting Power with Increasing the Terminal Chain Length of Achiral Bent-core Molecules doped in a Cholesteric Liquid Crystal

A series of non-chiral bent-core molecules with different alkoxy chain at the terminal positons were prepared, and we carried out doping experiments in a cholesteric liquid crystal (ChLC) phase mixed with the bent-core homologues. The helical twisting power (HTP) of the doped bent-core molecule in the ChLC strongly depended on the terminal alkoxy chain length of the bent-core molecules used in this study; Bent-core molecule with the longer alkoxy chain length shows the stronger HTP in a chiral circumstance such as a ChLC. Namely, not only the axial conformations at wings linked to bent central unit [1] but also the length of the alkoxy chain at the terminal positons of the bent-core molecules play an important role in showing the unusual chiral behavior. Details will be discussed in ACLC 2017.

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Paper No.  2017-TUE-P0101-P032
Sung-wook Jeon
Enhanced Chirality by Achiral Rod-like Smectic Phase Nanosegregated in the Helical Nano Filament Phase of Achiral Bent-Core Molecules

Chirality in a mixture system consisting of bent-core molecule (P8-O-PIMB) and rod-like molecule (8CB) molecules has been studied using circular dichroism (CD) observations. The observed CD spectra indicate as follows: (1) the CD signals originate from chiral-segregated helical nano filament (HNF) [1] of binary mixtures comprising bent-core P8−O−PIMB and rodlike 8CB molecules, where 8CB is in the isotropic phase; (2) the enhanced CD signal is detected in the BX1 phase of the binary achiral mixtures, where 8CB is in the nematic phase; (3) furthermore, remarkably enhanced CD signal emerged in the BX2 phase of the binary achiral mixtures, where 8CB is in the smectic phase. Details will be discussed in ACLC 2017.

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