In this study we investigated a new sorbent system, Azoic Direct Dye-attached poly(S-DVB functionalized)microbeads, for removal of heavy metal ions from aqueous solutions. Quaternary phosphonium salts grafted on a“gel-type”styrene-7%divinylbenzen copolymer were prepared by polymer-analogues direct quaternization reaction, and characterized by IR spectroscopy. A symmetric disazoic direct dye, containing 4, 4′-diaminobenzanilide as middle component and naphthionic acid as coupling component, was then attached to these microbeads. Microbeads carrying 1.33 mmol Azo Direct Dye/g polymer were used in adsorption/desorption studies. Adsorption rate and capacity of the microbeads for selected metal ions, i.e., Cu(II)and Zn(II), were investigated in aqueous media containing different amounts of these ions(6–200 ppm)at different pH values(2–7). Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 5–80 minutes. The maximum adsorptions of metal ions onto the azo direct dye attached microbeads were 2.9 mg/g for Cu(II)ions, and 53.8 mg/g for Zn(II)ions. Desorption of metal ions was studied by using 0.1 M HNO3solution(pH 1.0). High desorption ratios(more than 85%)were achieved in all cases. Adsorption/desorption cycles showed the feasibility of repeated use of this novel sorbent system.
Results are shown from computer simulations of droplets of model 8CB-like liquid crystal molecules in contact with a crystal surface. It is shown that the type of wetting observed depends on the strength of the interaction energy between the liquid crystal molecules an the substrate. For a low energy surface, partial wetting is found, and the liquid crystal forms a sessile droplet. However, for higher energies, the droplet spreads rapidly, forming a percursor layer and clearly defined molecular terraces. These results are qualitatively in line with experimental findings. The dynamics of spreading of the precursor layer have been examined, and the experimentally observed proportionality of the film radius on roott has been reproduced. However on examining the structure of the spreading layer, it is found that, at temperatures corresponding to a bulk smectic A phase, the spreading layer has a diamond shape, with edges perpendicular to the [110] directions in crystal surface. At higher temperatures, when the bulk system is in the isotropic phase, the spreading layer reverts to a radial symmetry.
Catalytic cross-dehydrocoupling polymerization of silane and water, and deaminative polymerisation between silanol and aminosilane are used to synthesize a variety of silicon-containing polymers with controlled structure.n-Hexylamine-2-ethylhexoate was used to catalyze silanol condensation. Among transition metal derivatives investigated, Pd2(dba)3is the most active catalyst for the dehydrocoupling polymerisation, and deaminative polymerisation proceeded smoothly by heating. Optically active siloxane materials of branched structure were obtained from(S,S)-1,3-dimethyl-1,3-diphenyldisiloxanediol and(S,S)-1,5-di(1-naphthyl)-1,5-diphenyl-1,5-divinyl-3-methyltrisiloxane(>99%ee)as optically active building blocks.
Non-symmetrical nickel(II) complexes containing a single acrylate or methacrylate motif have been synthesised and polymerised radically in tetrahydrofuran solution using AIBN as the initiator. This results in the incorporation of the metal complexes into a polyacrylate and a polymethacrylate as freely mobile side chains, free from cross-linking. Whilst the monomers are non-liquid crystalline, the polymers show smectic A liquid crystal phases.
A series of novel mesogens have been prepared by a five-fold Sonogashira reaction of terminal acetylenes with a functionalized pentabromophenol. The corresponding side chain polymers were prepared by a polymer analogous substitution reaction. The mesogens differ in the nature of the substituents, linking five hexyl tails to the aromatic core, i.e. CH2, O, S, SO2 and CONH groups. A wide range of mesophases and corresponding transition temperatures has been detected, ranging from low melting nematic phases to highly stable columnar phases. The widely variable phase behavior is described in terms of specific intermolecular interactions.
In the search for novel nematic liquid crystal materials for display applications, it is common to investigate several different alkyl chain homologues of a particular core structure. It is sometimes possible to develop a synthetic pathway that allows homologous variation in the ultimate step, but the majority of published methods for liquid crystal synthesis begin from an alkyl chain containing intermediate. This results in a separate pathway for each homologue. A “one-pot” technique has been developed for the parallel synthesis of up to five homologues of a given core structure, exemplified by “the 4-alkyl-4′-cyanobiphenyl series, together with their isolation in gram quantities and high purity by preparative high performance liquid chromatography. The technique demonstrates that it is possible to identify and monitor each intermediate throughout the synthetic pathway, using gas chromatography/mass spectrometry. It is also shown that there are no substantive losses in yield for any homologue throughout the pathway. It is concluded that this technique is a viable method for the synthesis of novel liquid crystal materials.
We have determined the in-plane molecular order of a polyamic acid (PAA) film irradiated with linearly polarized ultraviolet light (LPUVL), as well as that of the polyimide film obtained by thermally imidizing it. The PAA examined in this study contains azobenzene units in the backbone structure. The in-plane molecular order of the PAA and polyimide films was determined from the anisotropy in the polarized IR absorption of the phenyl C-C stretching vibration polarized along the backbone structure. We found that the photoinduced anisotropy in the in-plane molecular orientation was small, but it increased significantly after thermal imidization; i.e. the in-plane molecular order of the polyimide film was much greater than that of the PAA film. The enhancement of the in-plane molecular order was tentatively attributed to the crystallization of the film caused by thermal imidization.
We theoretically study interfacial properties between two coexisting phases in mixtures of a flexible polymer and a low molecular weight liquid crystal. By numerically solving Eular equations for concentration and orientation order parameters, we calculate order parameter profiles and interfacial tensions between coexisting nematic-isotopic and isotropic-isotropic phases at equilibrium.
We examined the conditions that produce no grayscale inversion over a wide-viewing-angle. We also examined the optimum conditions for a retardation film that compensates for the retardation of all LC cells in the dark state. Using these conditions, we realized a wide-viewing-angle, high-contrast LCD with a simple structure and high brightness.
The poly(p-phenylenevinylene)/polyurethane (PPV/PU) composite films obtained from water-borne PU system with PPV precursor (PrecPPV) were investigated. UV-VIS absorption, photoluminescence (PL), thermoluminescence (TL) spectra and dynamic mechanical analysis (DMA) results of pure PPV and its composite are reported and analysed. The conversion of the PrecPPV/PU into PPV/PU composite was confirmed also by mean of dielectric spectroscopy. It was concluded from the UV-VIS absorption and PL spectra at room temperature that the conjugation length of the PPV chains in this composite and in pure PPV is similar. In the PL spectra at low temperatures positions of the peaks are the same in the pure PPV and in the composite. Upon cooling all peaks shift towards longer wavelengths and change their relative intensities. The TL spectra show that in these materials relatively shallow traps dominate, yielding TL maximum at ca. 70 K. The composite films cast from water suspension are flexible in contrast to pure PPV which forms rigid film. In DMA it is reflected by lower values of the storage modulus E' and of the amplitude of tandelta in the composites compared to pure PPV film.
We report the results of recent experiments where for the first time X-ray microdiffraction has been used to probe liquid crystal ordering and nematic director-field configuration in single micron-sized droplets of polymer-dispersed liquid crystals. The pattern of the bipolar configuration has been detected in a droplet with radius R ≤⃒ 1 µm and the main quantities characterizing the orientational and short-range positional order of the confined nematic have been determined. We report a detailed description of the procedure followed to determine the distribution function of the nematic director in the droplet and the droplet order parameter from the azimuthal intensity profile of the diffraction pattern.
We studied the behaviour of polymer particles in a moving interface between the nematic(N)and isotropic(I)phases of a nematic liquid crystal(LC). We showed that theNI-interface is extended(E)and has a layeredN-I-Nstructure in the vertical cross-section of the sample; the wedge of the isotropic phase is bounded by the nematic phase, which is limited by the cell substrates. The minimum of the cell free energy defines the position of particles in the interface region. We find that the preferable position of the particle is at the vertex of the wedge formed by the isotropic phase. The particles are captured by the vertex line and follow the interface when it moves.
An improved liquid crystal lens is proposed. Two liquid crystal layers are used in the new lens. The power of the new lens is about twice as large as the former one.
We propose a new voltage-transmittance (V-T) curve suitable to determine the driving pulse shapes. There are three alternating periods in the multiplex driving scheme; a selecting period, a holding period and a resetting period. Holding pulse shape and holding period affect the switching behavior of AFLCs. In this paper a new V-T characteristics of AFLCs applicable in the design of multiplex driving scheme is examined, where a square pulse is used for both selection and holding voltages.
A three-dimensional numerical study for understanding the fringe-field effect on the dynamic behavior of liquid crystal is presented. Our three-dimensional numerical simulator (TechWiz LCD) is based on the FEM (finite element method) formulation of Ericksen-Leslie equation, flow equation, and Laplace equation. Since our FEM solver has a fully unstructured mesh generator, it is possible to investigate the dynamic performance of any mode of LC cell with an arbitrarily shaped electrode structure including a chevron-type LC cell. In this paper, we report our preliminary result on the simulation of the dynamic behavior of the fringe-filed switching (FFS) mode LC cell that is designed for the fast response and wide viewing angle. The simulated dynamic response of the director distribution for the FFS-mode LC cell is also compared with experimental observations. The simulation reveals that most of the directors over the LC cell experience horizontal rotations despite the existence of both the vertical and the horizontal electric fields in the LC cell.
Renormalized Transmission Ellipsometry CRTF,) was applied to a precise measurement of anisotropic refractive indices of nematic liquid crystals. It is quite important for the evaluation to use an monodomain cell with high quality. To realize the good alignment, the alignment film was coated. In this study, the influence of the alignment film thickness and its refractive indices on the accuracy of the measurement is reported. From the numerical analysis and several experiments, it is shown that if n(lambda) > n(0)(lambda) approximate to n(glass) (lambda) is satisfied and n(glass)(lambda) is nearly equal to n(al)(lambda), the evaluated results of n(0)(lambda) and n(e)(lambda) are not influenced by the film thickness d(al). From the results, RTE can be the powerfull tool to measure n(0)(lambda) and of n(e)(lambda) for the LC substances with easy operation.
New heterocyclic electron donors based on a 1,3,5-triazine nucleus are presented. Three phenyl rings are grafted to the triazine core either via secondary amino groups or by a direct C,C-linkage and a specific number of decyloxy chains is attached to the molecular periphery. The compounds are non-liquid crystalline in their pure states. Lamellar or columnar mesophases are induced by attractive interactions with electron acceptors.
We investigated effects of particle modification on physical properties of particle/liquid-crystal composites by polarizing optical microscopy and rheology. The surface modification of particles (ZrO2) was performed with an azobenzene carboxylic acid (8AB5COOH) in acetone. Surface coverage was evaluated as 56%. Under a polarizing microscope, the composites containing the surface-modified particle (8AB5COOH-ZrO2/8CB) exhibited characteristic textures in both smectic A (SmA) and nematic (N) phases. These textures could be observed repeatedly by changing the phase structures (SmA ↔ N) indicating the presence of strong coupling between the particle surface and 8CB molecules. In the rheological measurements, we observed cooperative changes of steady shear viscosity associated with isotropic → N phase transition in 8AB5COOH-ZrO2/8CB composites. With increasing the particle concentration, although the inherent discontinuous change of the viscosity around 42°C became small, a new characteristic change in the viscosity appeared around 46°C and became dominant. Effects of the shear rates on these changes suggest that structured regions may be formed with the modified particles. The viscosity change around 46°C would be attributable to the phase transition behavior of 8CB coupled with the particle surface in the structured regions. In addition, the morphology of the system can be reversibly modulated with the aid of the isomerization of the azobenzene moieties.
The first liquid crystal devices have recently been installed in the fibre optic networks that provide the backbone of the modern telecommunications system. Most optical network devices are concerned with the manipulation of the amplitude and phase of the optical signal. Liquid crystals have the highest figure of merit for field addressed electro-optic response and can have excellent transparency in, the optical telecommunications window.Here we consider the importance of liquid crystals in controlling the phase and the state of polarisation of light in these systems. We. also consider arrays of liquid crystal phase modulators, fabricated using LCOS technology, in holographic switches and multifuction devices.
Colloidal solutions containing fully redispersed crystalline In2O3: Sn (ITO) nanoparticles with an average size up to 30 nm and adequate organic binders (e.g. hydrolysable silanes) offer new possibilities to coat substrates with a transparent or antiglare conducting layer by different wet chemical coating techniques. The layers can be fully processed by UV light irradiation at low temperature (< 130 &DEG;C). The process allows to coat any types of transparent substrates which cannot withstand high temperature such as plastics ( tested with PC, PE, PMMA, PVC) and preformed glass substrates. The resistivity of these coatings is 5 x 10(-2) &UOmega; cm and comparable to that of commercial organic conducting polymers. Sheet resistance as low as 800 &UOmega;(&SQU;) and transparency in the visible range higher than 85% have been obtained for 600 nm thick single layers. The mechanical properties of these coatings is also reported. The coatings can be easily patterned at room temperature by soft photolithography technique.
