Liquid crystal alignment behaviours on poly(methyl methacrylate) having polyhedral oligomeric silsesquioxane groups

A series of poly(methyl methacrylate) derivatives containing polyhedral oligomeric silsesquioxane (POSS) groups (MCP#) were synthesised via free radical polymerisation (FRP) using methacryl isobutyl POSS (MA-POSS) and methyl methacrylate as monomers to investigate liquid crystal (LC) alignment property of these polymer films. The LC cells made from the films of the polymers having 100 mol% of MA-POSS units (MCP100) showed vertical LC alignment having a pretilt angle of about 90°. The vertical LC alignment behaviour on the MCP100 film was ascribed to the very hydrophobic MCP100 surface having the surface energy value smaller than about 23 mJ/m² generated by the nonpolar bulky POSS group. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), were observed for the LC cells fabricated using MCP100 as a LC alignment layer.     

Vertical alignment of liquid crystal on tocopherol-substituted polystyrene films

We synthesised a series of vitamin-based and renewable tocopherol-substituted polystyrene (PTOC#, # = 20, 40, 60, 80 and 100), where # is the molar content of tocopherol moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of tocopherol side group showed vertical LC alignment behaviour. The vertical alignment (VA) behaviour was well correlated with the surface energy value of these polymer films. For example, VA was observed when the surface energy values of the polymer were smaller than about 35.22 mJ/m² generated by the nonpolar tocopherol moiety having long and bulky carbon groups. Good electro-optical characteristics, such as voltage holding ratio and residual DC voltage, and aligning stabilities at 200°C and ultraviolet irradiation of 10 J/cm² were observed for the LC cells fabricated using PTOC100 as a LC alignment layer. Therefore, it was first found that the renewable tocopherol-based materials can produce an eco-friendly vertical LC alignment system.     

Liquid crystal alignment properties of poly(styrenesulphonate)/alkyltrimethylammonium complexes

We synthesised a series of poly(4-styrenesulphonate)/alkyltrimethylammonium (PSS-#Cx, # = 12, 14 and 16; x?=?80, 60, 40 and 20) complexes, where # is the number of carbon atoms in the alkyl groups in alkyltrimethylammonium bromide, and x is the molar content (%) of alkyltrimethylammonium moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a longer alkyl side group and a higher molar content of alkyl side group showed homeotropic LC alignment behaviour with a pretilt angle of about 90°. The homeotropic LC alignment behaviour was well correlated with the surface energy of the polymer films. Homeotropic LC alignment was observed when the surface energy values of the polymer were smaller than about 44.87 mJ/m².     

Liquid crystal alignment property of n‐alkylthiomethyl‐ or n‐alkylsulfonylmethyl‐substituted polystyrenes

We synthesized a series of n‐alkylthiomethyl‐substituted polystyrenes (#T‐PS, # = 4, 8, 12, and 16) and n‐alkylsulfonylmethyl‐substituted polystyrenes (#S‐PS, # = 4, 8, 12, and 16), where # is the number of carbon atoms in the n‐alkyl side group of the polymers, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a longer n‐alkyl side group, a thioether linkage group, and a higher molar content of n‐alkyl side group showed homeotropic LC alignment behavior with a pretilt angle of about 90°. The homeotropic alignment behavior was well correlated with the surface energy of the polymer films; when the positive dielectric anisotropic LC (ZLI‐5900‐000 from Merck) and negative dielectric anisotropic LC (MLC‐7026‐000 from Merck) were used to fabricate the LC cells, homeotropic alignment was observed when the surface energy values of the polymer were smaller than about 25 and 32 mJ/m², respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Liquid crystal alignment properties of n-alkylsulphonylmethyl-substituted polyoxyethylenes

The liquid crystal (LC) alignment properties of LC cells fabricated with films of n-alkylsulphonylmethyl-substituted polyoxyethylenes (#S-PEO, #?=?4, 6, 7, 8 and 10), where # is the number of carbon atoms in the n-alkyl side groups having different n-alkyl chain length, were investigated as a function of the rubbing density. The LC cells made from unrubbed #S-PEO (# ≥8) films having more than eight carbon atoms in the n-alkyl side groups showed homeotropic LC alignment. The homeotropic LC alignment behaviour correlated well with the surface energy values of the unrubbed #S-PEO films; homeotropic LC alignment was observed when the surface energy values of the unrubbed #S-PEO films were smaller than about 21.62 mJ m^?2. The LC cells made from rubbed #S-PEO (# ≥7) films having more than seven carbon atoms with a rubbing density of 150 showed homeotropic LC alignment. It was also found that the tilt angle of the LCs on the rubbed #S-PEO films was affected not only by the n-alkyl chain length of the polymers, but also by the rubbing density, regardless of the surface energy value of the #S-PEO film.     

Protic ionic liquid-based gel polymer electrolyte: structural and ion transport studies and its application in proton battery

Proton-conducting free standing gel polymer electrolyte (GPE) films containing protic ionic liquid, 1-butyl-3-methylimidazolium hydrogen sulphate, immobilized in blend of poly(vinylidenefluoride-co-hexafluoropropylene) and poly(vinylpyrrolidone) have been prepared by solution-cast technique. Films have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), complex impedance spectroscopy, and cyclic voltammetry. Ionic conductivity of the semicrystalline and porous GPE films has been obtained as ~3.9?×?10^?3 S cm^?1 at room temperature. Protonic nature of conduction in the films has been established by performing cyclic voltammetry and complex impedance spectroscopy on the cells having both blocking (stainless steel) and both reversible electrodes (Zn + ZnSO₄.7H₂O). The electrochemical stability window of the films has been found as ~3.8 V. The highest conducting film has been used as a separator and proton conductor to fabricate a proton battery of configuration Zn + ZnSO₄.7H₂O |GPE film| PbO₂ + V₂O₅. The battery shows an open circuit voltage of ~1.62 V. Energy density of the cell has been obtained as 35.2 W h kg^?1 for low current drain. Rechargeability of the cell has been tested for ten cycles. The maximum discharge capacity of the cell has been obtained as ~2.50 mA h g^?1 during the first discharge cycle.     

Study of dynamic light scattering in nematic liquid crystal and its optical,electrical and switching characteristics

In the present study, the polarisation-independent dynamic light scattering (DLS) in a nematic liquid crystal (LC) with a negative dielectric anisotropy has been compared in two operating modes by applying DC voltage or AC voltage to LC cells with a vertical and hybrid alignment. The attenuation of light transmittance and the DLS optical threshold without polarizers as well as a phase retardation of LC bend–splay deformation and a Fredericks threshold voltage with polarizers have been determined. Diffuse scattering of a light beam and broadband transmittance spectra of LC cells have been examined using the DC voltage in the interval of 0–40 V. Multi-domain structures and turbulent flows in the LC cells have been observed by polarisation optical microscope. The results show that the enhancement of the diffuse scattering of light in the LC cells correlate with ion density increase. The largest attenuation of the light intensity in the LC cells with a vertical alignment was 16.4 dB at a wavelength of 650 nm with a minimum decay time equal to 2.5 ms at DC voltage of 60 V. Our study has been shown that switching from a diffuse light scattering state to a transparent state can be twice accelerated by applying AC voltage with high frequency to LC cells.     

Effects of the fluorinated liquid crystal molecules on the electro-optical properties of polymer dispersed liquid crystal films

The different fluorinated liquid crystal (LC) molecules doped to E8 were used as LC component to prepare polymer dispersed liquid crystal (PDLC) films. The mass fraction of the LC mixture is fixed 50.0 wt%. Results indicate that doping 8.0 wt% fluorinated LC molecule ME3CP to E8 significantly reduced the driving voltage of the PDLC films, and the driving voltage reduced with the rise of mass fraction of ME3CP. Besides, the terminal flexible chain length of the fluorinated LC molecule influenced the LC mixture properties based on E8, such as the dielectric anisotropy, birefringence and viscosity of the LC mixture, and the morphology and the electro-optical properties of PDLC films were controlled not only by the physical properties of the LC mixture, but also by the terminal flexible chain length of the fluorinated LC molecule .     

In situ control of surface molecular order in liquid crystals using a localised polymer network and its application to electro-optical devices

A liquid crystal (LC) alignment technique has been developed that allows local control of the polar pretilt angle over the range of 0–90°. This was achieved through the formation of a polymer network localised in the vicinity of the LC cell substrates. The network was formed as a result of in situ UV-induced polymerisation of a photo-reactive monomer added at concentrations of 0.5–1%. Localisation of the polymer network at the LC–substrate boundary was achieved by the application of a high voltage before polymerisation. The resultant pretilt angle was determined by the voltage applied during the polymerisation and/or the duration of the voltage application before the polymerisation step. The desired pretilt angle could be set over a small area of the sample, which allows the fabrication of LC devices with spatially variable optical retardation. Using this method we fabricated a converging lens, a bi-prism, and a phase diffraction grating with resolution greater than 50 lines mm^?1.     

Dye-dependent studies on droplet pattern and electro-optic behaviour of polymer dispersed liquid crystal

In order to study the droplet pattern and electro-optic (EO) behaviour of polymer dispersed liquid crystal (PDLC) with the addition of dye, dichroic polymer dispersed liquid crystal (DPDLC) films were prepared using a nematic liquid crystal (NLC), photo-curable polymer (NOA 65) and anthraquinone blue dichroic dye (B2), in equal ratio (1:1) of polymer and liquid crystal (LC) by polymerisation induced phase separation (PIPS) technique. Dichroic dye was taken in different concentration (wt./wt. ratio) as 0.0625%, 0.125%, 0.25%, 0.5% and 1% of the LC mixture in DPDLC films. Initially, in an open circuit when there is no proviso for external electric field (0 V), LC droplets in polymer matrix exhibited bipolar pattern, though on closing the circuit with the increase of electric field pattern of droplets starts changing, LC molecules align along the direction of applied electric field and aligned completely relatively at higher field (30 V), which illustrate vertical radial pattern. Further, results show that the DPDLC film containing 0.0625% dye concentration with consistent average droplet size ~4.30 μm, exhibits the best transmission at lower operating voltage.     

偶氮聚合物表面起伏光栅用于液晶定向研究

液晶显示具有低功耗、高画质、轻巧等优点，广泛应用于各种平板显示装置．使液晶分子能在显示器中均匀的定向排列是液晶显示的关键技术之一．液晶定向技术的主要方法有摩擦法、SiOx等氧化物或Au、Pt等金属蒸镀法、紫外偏振光(或激光)辐照法等．所谓摩擦法，即通过将基片在均匀移动的丝绒布表面摩擦来实现的．一般认为摩擦法是通过摩擦在基板表面形成的微沟槽来诱导     

Polymer-dispersed liquid crystal composites for bio-applications: thermotropic,surface and optical properties

Polymer-dispersed liquid crystal (PDLC) systems based on polysulfone as carrying matrix and 4-cyano-4?-pentylbiphenyl (5CB) liquid crystal (LC) were obtained as thin transparent films. The PDLC films were prepared by solvent- and thermally induced phase separation methods, with various compositions in the two components. Information on the phase separation was obtained by polarised light optical microscopy, differential scanning calorimetry and scanning electron microscopy. The PDLC composites show well-defined droplets of submicrometric size, around 650 nm for a medium content of LC and around 250 nm for a low one. The droplets show a radial configuration and a homeotropic alignment of the LC molecules within. By contact angle measurement and surface free energy calculations, it was established that self-assembling of aliphatic units of the two composite components, at droplet interface, is the driving force of the homeotropic alignment. Moreover, these data indicated the potential biocompatibility of the studied composites. The photophysical behaviour shows a better light emission of the PDLCs containing bigger droplets.     

Optical,electrical, and electrochemical behavior of p-type nanostructured SnO<Subscript>2</Subscript>:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO₂ thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO₂ thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO₂ sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO₂ thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni²⁺ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm² (V s)^?1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO₂ thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2?×?10^?15 to 6.5?×?10^?15 cm² s^?1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.     

Ferroelectric liquid crystal composites based on the porous stretched polyethylene films

Electro-optically active polymer–liquid crystal composites based on ferroelectric liquid crystals and stretched porous polyethylene films were developed. The alignment of ferroelectric liquid crystals incorporated into the porous polyethylene films with average porous diameter of around 200 nm was observed and studied. It was shown experimentally that these samples containing ferroelectric liquid crystals are flexible electro-optical films exhibiting a saturation electric field near 2·10⁷ Vm^?1 and a response time of about 30 μs under the action of the saturation field. A simple theoretical model of ferroelectric liquid crystal molecules' complete reorientation in electric fields inside pores of the films has been proposed and confirmed experimentally.     

Proton-conducting membranes: poly (N-vinyl pyrrolidone) complexes with various ammonium salts

The present study focuses on the proton-conducting polymer electrolytes; poly (N-vinyl pyrrolidone)–ammonium thiocyanate and poly (N-vinyl pyrrolidone)–ammonium acetate prepared by solution casting technique. The XRD analysis indicates the amorphous nature of the polymer electrolytes. The Raman spectra of the C=O vibration of pure polymer PVP at 1,663 cm^?1 has been appeared as doublet in the polymer electrolytes. The introduction of this new peak in the salt-doped polymer electrolytes may be due to interaction of the cation with the polymer. The room temperature ionic conductivity σ _303κ has been found to be high, 1.7?×?10^?4 S cm^?1 for 80 mol% PVP–20 mol% NH₄SCN and 1.5?×?10^?6 S cm^?1 for 75 mol% PVP–25 mol% CH₃COONH₄. The polymer electrolytes have been tested for their application in Zn–air battery.     

Homogeneously aligned liquid crystal molecules on unidirectional buckle pattern of polyurethane films

We present the fabrication of an anisotropic structure on a polyurethane (PU) film for aligning liquid crystal (LC) molecules with ion beam (IB) irradiation at an incident angle. The obtained anisotropic structure assembles the LC cells in a layer that aligns LC molecules uniformly. Polarised optical microscopy images of an LC cell fabricated with IB-irradiated PU were captured to confirm the LC alignment state and compared with those fabricated with non-treated PU. To analyse the effects of the IB irradiation, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy were used to investigate the chemical and morphological modifications, respectively. IB irradiation modifies the chemical structure of PU, which indicates that a new skin layer is formed on the PU films. This skin layer generates an in-plane compressive strain, thereby creating buckles on the PU films. Simultaneously, the physical collision of the reactive Ar⁺ ions during IB irradiation induces a directional strain on the surface, thereby forming a unidirectional structure of buckles along the direction of IB irradiation. The PU film annealed at 200°C showed the high average transmittance of 88.9%, which is appropriate as an alignment layer.     

Novel self-dyed wholly aromatic polyamide–hydrazides covalently bonded with azo groups in their main chains

Thermal characteristics of several novel self-dyed wholly aromatic polyamide–hydrazides covalently bonded with azo groups in their main chains and containing o-hydroxy group as a substituent group in the aryl ring of the aminohydrazide part of the polymers have been investigated in nitrogen and in air atmospheres using differential scanning calorimetry, thermogravimetric analyses, infrared spectroscopy, and elemental analyses. The effect of introducing different predetermined proportions of para- and meta-phenylene moieties into the backbone chain of the polymers on their thermal characteristics has been evaluated. Azopolymers having different molecular masses of all para-oriented phenylene type units were also thermally characterized. These polymers were prepared by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide containing 3 % m v^?1 LiCl as a solvent at ?10 °C. All the polymers have the same structural formula except the mode of linking phenylene units in the polymer chain. The content of para- and meta-phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0–100 mol%. The results reveal that these polymers are characterized by high thermal stability and could be cyclodehydrated into linear aromatic polymers with alternating 1,3,4-oxadiazole and benzoxazole structural units within the same polymer approximately in the region of 200–480 °C, either in nitrogen or in air atmospheres by losing water from the hydrazide and o-hydroxybenzamide groups, respectively. Along with the cyclodehydration, the polymer may lose molecular nitrogen from the azo groups. This is not a true degradation, but rather a thermo-chemical transformation reaction of the evaluated polymers into the corresponding poly(1,3,4-oxadiazolyl-benzoxazoles). The resulting poly(1,3,4-oxadiazolyl-benzoxazoles) start to decompose in the temperature range above 330–560 °C, either in nitrogen or in air atmospheres without mass loss at a lower temperature. The thermal and thermo-oxidative stabilities of the polymers are affected by the nature and amount of arylene groups incorporated into their chains, being higher for polymers with greater content of para-oriented phenylene rings, which permits more interchain hydrogen bonds as a result of greater chain symmetry, packing efficiency, and rod-like structure. Increasing the content of para-oriented phenylene rings leads to a strong improvement in both the initial decomposition temperature as well as in the residual mass at a particular temperature. The stability of the polymers was found to be independent of their molecular masses. This confirms that high thermal stability is not a polymer property which would depends upon the length of its macromolecular chains, but rather upon its chemical structure in which all and every atomic group contributes by its own thermal stability to the macroscopic properties of the whole polymer.     

The effect of polymerizable surfactants on morphology and electro-optical of PDLCs films based on epoxy acrylate system

Polymer dispersed liquid crystals (PDLCs) have been extensively studied for various excellent electro-optical applications. The anchoring interaction of liquid crystals (LCs) molecules on the surface of the polymer cavity surrounding an LCs droplet has a crucial effect on the electro-optical performance of the PDLCs. The effect of polymerizable surfactants on the electro-optical properties of PDLCs films was studied in detail. The active double bonds were polymerized with prepolymer to stabilize the performance of polymer matrix. The experimental results showed that polymerizable surfactants could effectively reduce the driving voltage. The speed of polymerization was monitored by real-time transmittance. The electro-optical properties of PDLC films were measured by Polarimeter (PerkinElmer Model 341). The driving electric field was reduced from 3.9 V/μm to about 2.8 V/μm for doping undec-10-enoic acid at curing temperature 80?°C. The surfactants containing polymerizable functional groups, polarity, and alkyl chain weakened the surface anchoring between LCs droplets and polymer interface. The morphologies of PDLCs films were also investigated by polarizing optical microscopy (POM) and Fourier transform infrared (FTIR) images. The LC droplets were encapsulated by polymerizable surfactant according to FTIR images.     

Poly(o-phenylenediamine) thin film for organic solar cell applications

Poly(ortho phenylenediamine) (PoPDA) microrods with ladder-type structure are synthesized in acidic medium (pH?=?0.5) at room temperature based on a developed and facile method. The molecular structure, thermal stability, and surface morphology of the microrods-shaped PoPDA were described by different characterization techniques comprising FTIR, TGA, ¹HNMR, and SEM. Optimized thin films of PoPDA were successfully fabricated by thermal deposition method. The thin film was characterized by XRD and AFM. Au/PoPDA/p-Si/Al heterojunction diodes have been successfully fabricated. Dark current–voltage and capacitance–voltage characteristics were applied to get the particular parameters of the devices. Photovoltaic features of Au/PoPDA/p-Si/Al heterojunction at various intensities of white light illumination are studied. Under optimized conditions, the fabricated planar heterojunction solar cells utilizing a 95?±?10 nm of PoPDA film exhibited a power conversion efficiency (PCE) of ~?5.64% (J_SC?=?41.78 A/m², V_OC?=?0.36 V, and FF?=?28.11%). The relatively small FF (at room temperature with IP) and R_s of the devices designate that by increasing of the absolute temperature, the photovoltaic performance of the solar cells can be improved.