Farzana Ahmad

Investigation of nonionic diazo dye-doped polymer dispersed liquid crystal film

Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV–Vis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (V

Properties of thiol–vinyl PDLC films without additional photoinitiator

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Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles

, increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.

Current trends in studies on reverse-mode polymer dispersed liquid-crystal films — A review

Polymer-dispersed liquid crystal (PDLC) films block UV light and have been used as smart windows, light shutters and rear screens on buildings. Generally, PDLCs are fabricated by photopolymerisation using photoinitiators (PIs), which may induce film degradation by UV light. In this study, we report the fabrication of thiol–vinyl PDLC films by the polymerisation-induced phase separation method without the addition of PI. The stoichiometric ratio of the thiol and vinyl monomers was optimised based on variations in the FT-IR absorbance intensity. The fabricated films displayed good electro-optical properties. The durability of the PDLC films (with and without PI) was investigated by observation under UV irradiation for 10 days, following which the films were characterised using a spectrophotometer, scanning electron microscope and polarised optical microscope. The thiol–vinyl PDLC film without PI exhibited good physicochemical durability and low haze variation under UV irradiation.

Characteristics of di- and tri-block copolymers: polymer disperse liquid crystal display

In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical properties for reflective D-PDLC displays at lower viewing angles below 30°.

Effect of cetyltrimethylammonium bromide coatings on indium tin oxide surfaces in reverse mode polymer dispersed liquid crystal films

Reverse-mode polymer dispersed liquid crystals (PDLCs) comprise an important new class of materials for optical device applications. Generally reverse-mode PDLCs are transparent and opaque in the absence and presence of an external field, respectively. Display devices based on reverse-mode PDLC technology are useful for large-area displays; because their fabrication for manufacturing shutters is considered to be easier and faster, they are also employed for automotive technology and smart windows. These devices can be operated at a low voltage, which conserves energy in intelligent-device applications. This work presents a comprehensive review of past research regarding reverse-mode PDLCs and includes the advantageous features, applications, and various fabrication methods of reverse-mode PDLCs and photo-chromic reverse-mode PDLCs. In addition, some new features of this technology that have recently been reported and future investigations by a variety of research groups are presented.

Magnetically driven vertical alignment of liquid crystals by ferromagnetic particles

In the reported work the block copolymers are used in the polymer disperse liquid crystal (PDLC) films. The present work has been performed to investigate the effect of block copolymer addition and block ratios on the PDLC characteristics. From our experimental finding, addition of block copolymer in PDLC shows variation in droplet size, electro-optical properties, extent of phase separation, and phase transition temperature. These finding indicate the alteration in solubility parameters of solutions with the addition of block copolymers. Moreover, the tri-block copolymer shows enlarge droplet size, enhancement in the degree of phase separation, and predict improvement in electro-optical properties, as compared to di-block copolymer. Similarly upon such comparison, the study suggests the tri-block copolymer have a relative lower molecular interaction with the liquid crystal molecules.

The effect of UV intensities and curing time on polymer dispersed liquid crystal (PDLC) display: A detailed analysis study

The vertical alignment of liquid crystals (LCs) on cetyltrimethylammonium bromide-coated (CTAB-coated)indium tin oxide (ITO) glass is the consequence of specific interactions between the LCs, CTAB and ITO surface. The CTAB concentration influences the LC orientation, which changes the ITO surface energy. Changes in the surface energy of CTAB-coated ITO glass are investigated by the Owens–Wendt method. Both polar- and dispersive-component energies on the ITO surface decrease as the CTAB concentration increases, and reach saturation around 0.002% CTAB. The physico-chemical interaction between the LCs and the ITO surface was diminished by the presence of the CTAB layer, which induced the vertical alignment of LCs having positive or negative dielectric anisotropy. Vertical alignment is confirmed using crossed polarisers and the crystal rotation method. The electro-optical properties of fabricated reverse mode polymer dispersed liquid crystal films display transmittance of Ton: 29.7%, Toff: 85% and a response time of τon: 33 ms, τoff: 107 ms.

Physicochemical properties of long-hydrocarbon-chain- silane-coated indium tin oxide glass for reverse-mode polymer-dispersed liquid crystals

We propose a simple methodology to vertically align nematic liquid crystal (LC) molecules by a single-step process. This is achieved by dispersing a small amount of ferromagnetic particles in LCs under a weak magnetic field. For this purpose, a magnetic field of 0.1T is applied for 5 min. The resulting vertical arrangement of LC molecules was confirmed by a cross-polarised optical microscope, Fourier transform infrared analysis and the optical transmittance of polymer-dispersed liquid crystal films.

Rotational viscosity calculation method for liquid crystal mixture using molecular dynamics

In current study polymer dispersed liquid crystal (PDLC) films whose composition based on nematic liquid crystal (LC) E7 and prepolymeric NOA65 were formed via the photo induced phase separation method, in a wide intensity range of the UV light (I = 0.33-1.8 mW/cm2) and curing duration (t = 120-600 sec). The PDLC characteristics were monitored by surface morphology, electro optical studies, as well as by phase separation process through measuring the FTIR absorption of the composite layers. Increase of curing light intensity accelerates the phase separation and drastically influences the final morphology of LC droplets inside PDLCs. Likewise by widening the curing duration the enhancement in phase separation was observed. Increase of light intensity from 0.89 mW/cm2 and duration t = 120-240 sec resulted into transition from large LC domains of irregular shape (due to aggregation of droplets) to fine mono dispersed LC droplets. This morphology caused increase in optical scattering on zero voltage and high driving voltage. However unexpectedly, this response was not directly related with the curing conditions (intensity and time). These findings extend the potential applications of thiol-ene based PDLCs.