Influence of cell and LC parameters on the dynamics of STN liquid crystal displays

The dynamics of super-twisted nematic (STN) liquid crystal displays have rarely been studied. In this article, the dynamic response of STN is analysed in detail. The evolution of director configuration with time was obtained by solving Ericksen–Leslie hydrodynamic equations. The time varying midlayer tilt angle is presented as a measure of dynamic response. The influence on STN dynamics of cell parameters including pretilt angle, twist angle, cell thickness, and of material parameters including d/p, K ₂₂, K ₃₃, were studied.     

Cyano terminated tolane compounds for polymer dispersed liquid crystal application: relationship between cyano terminated tolane based molecular structures and electro-optical properties

ABSTRACT

The structures of the liquid crystal (LC) molecules have a key role in impacting the electro-optical performance of a polymer dispersed liquid crystal (PDLC) film. In this paper, the relationship between the LC molecular structures and the electro-optical properties of PDLC films is investigated based on an unexplored cyano-terminated tolane compounds (CTTCs) doped E8 LCs/UV polymers system. Due to the high polarity of CTTCs, LCs doped with the cyano-terminated tolane (CTT) molecules exhibit high birefringence and large positive dielectric anisotropy. On the whole, PDLC films doped with the CTT molecules exhibit a lower driving voltage than that doped with the pure E8. More excitingly, PDLC films based on CTT molecules with larger length-to-width ratio and longer conjugated system show higher contrast ratio (CR) and faster response time. Eventually, the mechanism of the effects of CTT-based molecular structures and the relationship between the electro-optical performance of PDLC films and CTT molecules are illustrated. This work paves a new way for optimising the electro-optical properties of PDLC films.     

Sol–gel derived ZnO nanoparticulate films for ultraviolet photodetector (UV) applications

Zinc oxide nanoparticles based UV detector was fabricated on thermally oxidized silicon substrate. ZnO nanoparticle films were deposited using sol–gel route. The seed solution was prepared using two different solvents (methanol and isopropyl alcohol (IPA)). The surface morphology of the prepared films was characterized by FESEM. Structural characterization along with optical measurements was carried out using XRD and UV–vis spectroscopy. For the UV photo-detector, ZnO thin film prepared in IPA is selected based on their structural and optical analysis. The changes in photo-response of ZnO thin film with respect to time was studied under the dark and variable UV intensities. It was observed that the photocurrent increased with a factor of 4.82 under 1.16 mW of UV intensity. It is believe that the synthesized ZnO thin films have potential to use in the ultraviolet photo-detector applications.     

Corrigendum on ‘investigation on molecular interaction studies of binary mixture of Dehpa and Petrofin at 298.15 K’

Expressions of Redlich–Kister (RK) excess function using polynomials on difference of molar composition are used. Calculated values of excess properties from experimental values are well presented in some curves as a function of mole fraction (x₂) of the second pure component of the studied binary liquid mixture. Nevertheless, the authors presented values of adjustable parameters, not for the polynomial of the popular RK equation (i.e. vs. x₂–x₁), but for globally the excess property Y^E as an overall three degree polynomial on (x₂) including implicitly the molar fraction product (x₁·x₂) in their nonlinear regression, which can then induces some readers to probable confusion.     

Dielectric properties of selected laterally fluoro-substituted 4,4′′-dialkyl,dialkoxy and alkyl-alkoxy [1:1′;4′:1′′]terphenyls

Measurements of the complex permittivity, ε*?=?ε′ – iε″, within the frequency range 200 Hz to 10 MHz for 15 laterally fluoro-substituted terphenyls have been conducted. In most cases the substances exhibited the nematic phase over a broad temperature range. All substances were characterised by negative dielectric anisotropy, and are potentially useful for vertical alignment mode systems. The static permittivity tensor components have been analysed in relation to the dipole structure of the molecules. Dielectric relaxation processes observed in the liquid crystalline (LC) and solid rotator (R) phases (obtained by slow cooling of the samples) are characterised by calculation of the relaxation times and activation barriers. The rotation motions around the short axes are typical for LC phases, whereas rotations about the long axes, accompanied in some cases by internal motions, are present in the R phase.     

Electroactive Polymers: Developments of and Perspectives for Dielectric Elastomers

We present the development and applications of dielectric elastomers. For the last 10 years the significance of this class of polymers has risen as more applications seem possible and first products have been commercialized.     

Reflective mode of deformed-helix ferroelectric liquid crystal cells for sensing applications

We present a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers. Using a model based on the effective dielectric tensor approximation, we derive simple analytical formulas to design a LC cell with maximum modulation depth and optimal linearity of the electro-optical response intensity versus the electric field. Our experimental results show that the cell works at frequencies up to 10 kHz and exhibits excellent linearity, with a total harmonic distortion as low as ?70 dB. These findings suggest that DHF-LCs can be exploited to develop simple and accurate optical sensors.     

Nickel(II) complexes of N-(dialkylcarbamothioyl)-4-nitrobenzamide as single-source precursors for the deposition of nanostructured nickel sulfide thin films by chemical vapor deposition

Nickel(II) complexes of N-(di-alkyl-carbamothioyl)-4-nitrobenzamide (alkyl?=?ethyl or n-propyl) have been synthesized and characterized by infrared spectroscopy, elemental analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The structures of bis[N-(diethylcarbamothioyl)-4-nitrobenzamide]nickel(II) (2a) and bis[N-(dipropylcarbamothioyl)-4-nitrobenzamide]nickel(II) (2b) have been determined by X-ray crystallography. FTIR and NMR of the nickel complexes showed the absence of the N–H proton resonance and the N–H stretch and shift of ν _C=O and ν _C=S as expected. Both complexes have been used as single-source precursors for the deposition of nickel sulfide nanostructured thin films by aerosol-assisted chemical vapor deposition. The nanostructured thin films were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and atomic force microscopy.     

Migration of indium ions in amorphous indium-gallium-zinc-oxide thin film transistors

Electromigration of In in amorphous indium-gallium-zinc-oxide thin film transistors under repeated switching operation was investigated by analyzing the distribution of component elements. During the repeated switching operations up to 300 times, threshold voltage of this device increased gradually implying alteration to the internal device structures. Energy dispersive X-ray spectroscopy revealed noticeable redistribution of metallic components, especially In, in the channel layer beneath the source electrode during switching operations by the migration of metallic ions away from the source electrode, which is attributed to electromigrations similar to those observed in organic light emitting diodes having indium tin oxide electrodes.