Doping effects of fluorinated chiral dopant in blue phase liquid crystals and its electro-optical behavior

ABSTRACT

We reported a fluorine-containing binaphthyl derivative, denoted as BD-F, which showed a low helical twisted power. The blue phase liquid crystal (BPLC) doped with BD-F achieved a lower operating voltage than that only used traditional chiral dopant, resulting from the larger dielectric property of fluorinated BD-F. In addition, the BPLC composite exhibited a wider temperature range and an enhanced Kerr effect with the decreased frequency. In terms of the applications, the devices revealed microsecond response time, thereby providing broad prospects for photonics and displays.     

Polarisation-independent blue-phase liquid crystal microlens array with different dielectric layer

A fast response (sub-milliseconds) and polarisation-independent blue-phase liquid crystal (BPLC) microlens array with periodical double layer electrodes using different dielectric layers is proposed. The bottom double layer electrodes are coated with transparent and different dielectric layers to generate linearly varying electric potential from the centre to the edge, while the top planar electrode iridium tin oxide (ITO) electrode has a constant potential. As a result, gradient vertical electric fields are generated, and a gradient refractive index profile is obtained. When the applied voltage is changed, the focal length of the BPLC microlens array can be tuned from ∞ to 12.05 mm while keep a low operating voltage (~35V_rms). Besides, the driving mode (simplification driving) and fabrication process (using printing method or mold-pressing method) of the BPLC microlens array is very simple. The simulation results show that the BPLC microlens array is insensitive to the polarisation of incident light while keeping parabolic-like phase profile.     

A hysteresis-free polymer-stabilised blue-phase liquid crystal

We report a polymer-stabilised blue-phase liquid crystal (BPLC) in an in-plane-switching (IPS) cell with negligible hysteresis and good stability. Long ultraviolet (UV) wavelength and top-side (no IPS electrode) exposure create uniform polymer network, which in turn helps to suppress hysteresis. The effect of photoinitiator is also investigated. Although a BPLC precursor without photoinitiator requires a higher UV dosage to stabilise the polymer network, it is favourable for keeping high resistivity and reducing image sticking.     

Blue-phase liquid crystal display with high dielectric material

A blue-phase liquid crystal display (BPLCD) with low operating voltage and high transmittance is demonstrated by using a high dielectric material, which is used as an insulation layer or protrusion fixed on the pixel and common electrodes in in-plane switching (IPS) mode. The operating voltage is reduced to about 14 V and the transmittance is improved for the BPLCD with high dielectric constant protrusion. Compared with the conventional protrusion electrode structure, the proposed protrusion can make manufacturing process simple and easy because the electrode has no complex shape. The results will be significant in designing optimal BPLCDs.     

Reflective blue phase liquid crystal displays with double-side concave-curved electrodes

Reflective blue phase liquid crystal display (BPLCD) is a promising candidate for field sequential colour displays with reflective liquid-crystal-on-silicon (LCoS). However, the issue of high operation voltage still hinders its widespread applications. We propose a reflective BPLCD with double-side concave-curved electrode and research its operation voltage and electro-optic characteristics in simulation, which is compared to the transmissive mode. The effect of double-side electrodes on horizontal electric field and operation voltage is analysed. The improvement of concave-curved electrodes on reflectance is discussed. A reflective BPLCD has two times the optical path difference compared to the transmissive mode. By using double-side concave-curved electrodes, the reflectance increased by 23% and the operation voltage reduced by 32% compared to the traditional in-plane switching mode. This work enables BPLC to be integrated with reflective LCoS.     

The effects of silica nanoparticles on blue-phase liquid crystals

We investigate the effects of hydrophobic silica nanoparticles (SNs) on blue-phase liquid crystals (BPLCs). The optical microscope and reflection spectra observation reveal that a tiny hydrophobic SN dopant stabilises the BPLC phase, and widens the temperature range of the BP I phase. Furthermore, the doped dilute SNs can fine-tune their positions to relax the formation stress of the BPLC lattices, and slightly increase the platelet sizes of the BPLCs. The doped SNs also decrease the driving voltage and response time of the BPLC cell, because the added SNs decrease the elastic constant of the LC host and the relaxation time constant of the BPLC mixture.     

One-dimensional model for simulating blue-phase liquid crystal display

We proposed a one-dimensional model for simulating some performances of blue-phase liquid crystal (BPLC) and polymer-stabilised blue-phase liquid crystal (PSBPLCD). The one-dimensional model treats liquid crystal arrangement of BPLC as cholesteric liquid crystal with high and uniform tilt angle to simulate the Bragg reflection of BPLC. The simulated results agree quite well with the experimental results. The elastic and dynamical equations are formed to calculate the effective elastic parameters and the response times of PSBPLCD. The effective elastic parameter is a constant for low electric field and decreases with the increasing of electric field. The varied effective elastic parameter means the varied restoring force of liquid crystal under the electric field. The dynamical equations are proposed to calculate response times, and the response mechanism of BPLCD is discussed by researching the difference between the decay times from equation and experiment. The sub-millisecond response time results from the weak anchoring of polymer network or the increasing of rotational viscosity of PSBPLC with high-concentration monomer, and the reason of 10 µs response time is the strong anchoring and small amount of chiral dopant and monomer.     

Blue-phase liquid crystal display with insulating protrusion

In order to lower the saturation voltage and enhance the transmittance of in-plane switching blue-phase liquid crystal display (IPS-BPLCD), IPS-BPLCD with insulating protrusion is proposed. The single-protrusion (only set on the top of pixel electrode) and double-protrusion (set on the top of pixel and common electrodes) structures are investigated in this work. The potential distribution changes when the protrusion is used. There is a thicker transverse electric field in BPLC range, because the stronger electric field at the edges of the electrodes is decentralised into BPLC range. As a result, the saturation voltage is reduced from 36.3 V to 28.9 V when the double-protrusion structure is used, and transmittance is increased by ~20%. The contrast ratio is larger than 1000:1 in 60° viewing cone using a half-wave biaxial film. Both single-protrusion and double-protrusion structures have the uniform gamma curves at large oblique viewing angles. Moreover, the off-axis image distortion index is 0.1590 at 60º polar angle when zigzag electrodes are used.     

A blue-phase liquid crystal lens array based on dual square ring-patterned electrodes

We propose a blue-phase liquid crystal (BPLC) lens array based on dual square ring-patterned electrodes. A high dielectric constant layer is used to smoothen out the horizontal electric field and reduce the operating voltage. By creating a potential difference between the dual square ring-patterned electrodes, gradient electric fields are generated and lens-like phase profile is obtained. Besides, the focal length of the BPLC lens is adjustable with voltage changes and all simulation results indicate that the BPLC lens array is polarisation-insensitive.     

Electrochemical behavior of new electrode material: Compact of boron-doped synthetic diamond

Electrochemical properties of new electrode material—compact of boron-doped synthetic diamond—is studied for the first time. Cylindrical samples 3.5–4 mm in diameter and 2.5 mm in height were obtained by thermobaric processing of graphite–boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8–9 GPa and temperature of ~2500 K). Their electrode behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammograms of the compact samples showed that their electrode characteristics are similar to those of traditional thin-film diamond electrodes obtained by the chemical vapor deposition (CVD) technique. In particular, they demonstrate rather wide potential window, low background current in indifferent electrolytes, and good reproducibility. It can be concluded that the diamond compacts practically are not inferior to the thin-film CVD-diamond electrodes and can serve as indicator electrodes, e.g., in electroanalysis. At the same time their compact form may be a convenience in the designing of electrolyzers and other electrochemical devices.     

Edge Plane Pyrolytic Graphite Electrodes for Stripping Voltammetry: a Comparison with Other Carbon Based Electrodes

The first examples of using edge plane pyrolytic graphite electrodes for anodic and cathodic stripping voltammetry (ASV and CSV) are presented, notably the ASV of silver and the CSV of manganese. In the former example, detection limits for silver (based on 3σ) of 8.1 nM and 0.185 nM for 120 s and 300 s accumulation time, respectively, were achievable using the edge plane electrode, which were superior to those observed on glassy carbon, basal plane pyrolytic graphite and boron‐doped diamond electrodes. In the second example, a detection limit for manganese of 0.3 μM was possible which was comparable with that achievable with a boron‐doped diamond electrode but with an increased sensitivity. Comparison of the edge plane pyrolytic graphite electrode with boron‐doped diamond electrodes reveals that the edge plane electrode has comparable detection limits and sensitivities whilst exhibiting a lower signal‐to‐noise ratio and large potential window for use in trace analysis suggesting boron‐doped diamond can be conveniently replaced by edge plane pyrolytic graphite as an electrode material in many applications.     

Electrochemical oxidation and determination of methylparaben at overoxidized polypyrrole film modified a boron-doped diamond electrode

Electrochemical oxidation of methylparaben (MP) is studied on an overoxidized polypyrrole (OPPy)-modified boron-doped diamond electrode using the cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. The OPPy-modified BDD electrode displays the catalytic activity of electrooxidation of methylparaben. The modification of BDD electrode surface results in higher values of recorded oxidation currents of the methylparaben than on a bare BDD electrode. The diffusion character of recorded current is determined on the basis of the relation between the current and the scan rate. The linear relationship between methylparaben oxidation peak current is obtained in the range 1.57?×?10^??6–2.06?×?10^??5 mol L^??1. A new voltammetric procedure is proposed to quantify methylparaben in cosmetic products using an overoxidized polypyrrole (OPPy)-modified BDD electrode. The results are compared to the HPLC technique described in the literature as the reference method.     

High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite

We demonstrated a relatively simple and effective method to fabricate a periodically isolated polymer wall of blue-phase liquid crystal Fresnel lens (BPLCFL) by employing a single-masking process of the ultraviolet (UV) irradiation, leading to excellent photopolymerisation-induced phase separation between blue -phase liquid crystal (BPLC) molecules and UV-curable monomers. Nevertheless, some uncured monomers would inherently reside in the BPLC-rich area and slightly inhibit the BPLC molecules realigned under the external electric field. To enhance the optical properties of the polymer-wall BPLCFL considerably, a novel technique for fabricating a pure BPLC zone is proposed that successfully expels the residual monomers from the BPLC volume using a thermal annealing process. Experimental results show that the maximum diffraction efficiency reaches ~36%, which approaches the theoretical limit of ~41%. Consequently, the annealing technique to purify phase-separated composite films has a strong potential to construct the BPLCFL in light of polarisation-free applications.     

A polarisation-free blue phase liquid crystal lens with enhanced tunable focal length range

A polarisation-free blue phase liquid crystal (BPLC) lens with enhanced tunable focal length range is proposed. A matched conventional glass lens is introduced on a BPLC lens to increase the range of the tunable focal length. The focal length of the BPLC lens can be switched from positive to negative, the negative lens-like phase profile can be neutralised by the conventional glass lens to get an infinity focal length and the positive lens-like phase profile can be enhanced by the conventional glass lens to get a shorter focal length. The minimum focal length can be decreased to almost half of that after the proposed method is adopted in our simulation. Moreover, the proposed BPLC lens exhibits a good polarisation-free feature and the optical effect is relatively good.     

Fabrication and electrochemical behaviour of vertically aligned boron-doped diamond nanorod forest electrodes

Vertically aligned boron-doped diamond nanorod forests (BDDNF) were successfully fabricated by depositing a diamond film onto silicon nanowires (SiNWs) using hot filament chemical vapor deposition (HFCVD). The boron-doped diamond nanorods were characterized by Raman spectroscopy and scanning electron microscopy (SEM). The BDDNF obtained from the SiNWs on the silicon wafer could be directly used as an electrode and its electrochemical behaviour is discussed here. Compared to a flat boron-doped diamond (BDD) electrode, the BDDNF electrode showed high sensitivity in the amperometric detection of adenine.     

Whole cell environmental biosensor on diamond

A whole-cell environmental biosensor was fabricated on a diamond electrode. Unicellular microalgae Chlorella vulgaris was entrapped in the bovine serum albumin (BSA) membrane and immobilized directly onto the surface of a diamond electrode for heavy metal detection. We found that the unique surface properties of diamond reduce the electrode fouling problem commonly encountered with metal electrodes. The cell-based diamond biosensor can attain a detection limit of 0.1 ppb for Zn(2+) and Cd(2+), and exhibits higher detection sensitivity and stability compared to platinum electrodes.     

Pyrolytic graphite electrode modified with a thin film of a graphite/diamond nano-mixture for highly sensitive voltammetric determination of tryptophan and 5-hydroxytryptophan

We have prepared a pyrolytic graphite electrode (PGE) whose surface is covered with a thin film of a nano-mixture of graphite/diamond (NGD). The electrode is shown to be capable of electrochemically sensing of tryptophan (TRP) and 5-hydroxytryptophan (HTRP). The presence of the NGD film resulted in a remarkable increase in the peak currents and sharpness of the waves so that submicromolar concentrations of TRP and HTRP become detectable. Potential scan rates, the pH of the solution, the accumulation conditions and the amount of the modifier were optimized via cyclic voltammetry. Linear sweep voltammetry, under optimized accumulation time and in open circuit operation, was applied to the determination of TRP and HTRP with detection limits (S/N = 3) of 30 nM (TRP) and 6 nM (HTRP). The electrode can be easily prepared, displays high sensitivity, sharp peaks, long-term stability, and remarkable voltammetric reproducibility and repeatability. These properties make the sensor suitable for the trace analysis of TRP and HTRP in pharmaceutical and clinical preparations.

A pyrolytic graphite electrode modified with a thin film of a nano-mixture of graphite/diamond. This electrochemical sensor applied for determination of tryptophan and 5-hydroxytryptophan in aqueous solutions. The modified electrode showed a remarkable increase in the peak currents and sharpness of the waves.

     

Aligned Pt-diamond core-shell nanowires for electrochemical catalysis

Heavily boron-doped diamond electrode has been applied as a robust substrate for Pt based catalyst. However, by simply applying a planar electrode the effective surface area of the catalyst is limited. In this article we for the first time prepared vertically aligned Pt-diamond core-shell nanowires electrode in a convenient and scalable method (up to 6-inch wafer size). The diamond nanowires are first fabricated with reactive ion etching with metal nanoparticles as etching masks. The following Pt deposition was achieved by DC sputtering. Different amounts of Pt were coated on to the nanowires and the morphology of the core-shell wires is characterized by SEM and TEM. The catalytic oxygen/hydrogen adsorption/desorption response are characterized by cyclic voltammetry. The results show that the active Pt surface area is 23 times higher than a planar Pt electrode, and 4.3 times higher than previously reported on Pt nanoparticles on diamond by electro-deposition. Moreover, this highly active surface is stable even after 1000 full surface oxidation and reduction cycles.     

Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system.

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.     

Pt-polyaniline nanocomposite on boron-doped diamond electrode for amperometic biosensor with low detection limit

Boron-doped diamond electrodes covered with a nanostructured Pt nanoparticle-polyaniline composite have been fabricated and employed as sensitive amperometric sensors with low detection limit. A highly conductive boron-doped diamond thin film (BDD) was prepared by chemical vapor deposition, and its morphology was characterized by scanning electron microscopy and transmission electron microscopy. The nanostructured composite layer was grown on the BDD electrode by electrochemical deposition of polyaniline and Pt nanoparticles. Glucose oxidase (GOx) was then adsorptively immobilized on the modified BDD electrode. The biosensor displays a large surface area, high catalytic activity of the Pt nanoparticles, efficient electron mediation through the conducting polymer, and low background current of the electrode. The biosensor exhibits an excellent response to glucose, with a broad linear range from 5.9 μM to 0.51 mM, a sensitivity of 5.5 μA·mM^?1, a correlation coefficient (R) of 0.9947, and a detection limit of 0.10 μM. The apparent Michaelis-Menten constant (K _M ^app ) and the maximum current density of the electrode are 4.1 mM and 0.021 mA, respectively. This suggests that the immobilized GOx possesses a higher affinity for glucose at the lower K _M ^app , and that the enzymatic reaction rate constitutes the rate-limiting step of the response.