A model of active acid-base surface sites for zinc sulfide electroluminescent phosphors

Results of studies into surface properties of ZnS: Cu,Al and ZnS: Cu electroluminescent phosphors by the indicator method were summarized. The surface and electrooptical properties of these phosphors were examined in relation to the reaction batch composition and synthesis atmosphere, as well as to heat-treatment and electron-beam-induced modification regimes. On this basis, the structure of the surface active sites having different acid powers was established, and a surface model for zinc sulfide electroluminescent phosphors was proposed.     

Atomic absorption spectrophotometry of zinc sulfide:Silver phosphors

An AD converter was interfaced between a conventional instrument of atomic absorption and microcomputer. The system can measure signals within a full-scale precision of 0.4%. For a single measurement only a small volume of sample solution, down to 200 μl. is aspirated. Backgrounds and atomic absorption signals are determined after averaging 64 binary data samples from a single measurement. Results of analysis are printed out by computer calculation after the measurements.The system was applied to the analysis of zinc sulfide phosphors having different particle sizes and structures. Differences in the chemical composition were found, for example, the largest size particles had a lower silver content and a higher sodium content than the medium and smaller size particles.     

Effect of oligomeric surface modifying agent on electro-optical properties of polymer dispersed liquid crystal

In order to lower the driving voltage of polymer dispersed liquid crystal (PDLC), an oligomeric surface modifying agent (SMA) which is a fluoroalkyl terminated polyurethane (PU) oligomer has been synthesized and added to polyurethane acrylate (PUA) resin. With the addition of SMA, contact angle of the resin surface with an LC drop increased and domain size decreased significantly due to the enrichment of SMA molecules at the surfaces. Operating voltage decreased up to 5 phr SMA and increased beyond this content. Regarding the effect of SMA molecular weight, lower molecular weight drove the shutter at lower operating voltage, indicative of more enrichment of the SMA molecules at the surfaces.     

Preparation of copper and zinc sulfide nanoparticles and their modification with cysteine

A new method for the preparation of copper and zinc sulfides nanoparticles in homogeneous aqueous solutions using cysteine as a surface modifier was proposed. The size of the particles obtained is 5–7 and 1.5–3 nm for copper and zinc sulfides, respectively, depending on the concentration of the reactants. Associates of the nanoparticles 10–30 nm in size are formed in the system with an increase in the total concentrations of the sulfides. Sols of the nanoparticles obtained in cysteine solutions are resistant to oxidation and coagulation within several weeks. The variation of the synthesis conditions makes it possible to obtain zinc sulfide particles with optical properties related to size effects.     

Relationships of lignosulfonate adsorption onto the zinc sulfide surface

Low-molecular-mass lignosulfonates (M _w = 9250 amu) are adsorbed more strongly onto ZnS from neutral solutions (pH 4.5–4.8), and high-molecular-mass lignosulfonates (M _w = 46300 rpm), from acid solutions (pH 1.4–1.5). The sorption of the low-molecular-mass sample at pH 1.5 is affected by competing sorption of the solvent (Н₂SO₄). The lignosulfonate samples studied are adsorbed onto zinc sulfide by the chemisorption mechanism.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Effect of shock-wave treatment of zinc sulfide on properties of ZnS:Cu,Mn phosphor

Method was developed for raising the brightness of photo- and electroluminescence from ZnS:Cu,Mn phosphor in dc and ac fields by preliminary shock-wave treatment of a starting zinc sulfide placed in a closed copper ampoule.     

Miscibility of zinc sulfide and zinc phosphide

Solid solutions in the system zinc sulfide/zinc phosphide (Zn(2+)(x)S(2-2xP(2x)) were investigated using the cyclic cluster model within the semiempirical MSINDO method. Results of cyclic cluster calculations for binding energies of the perfect ZnS and Zn(3)P(2) are presented and compared with the experimental data. The miscibility of ZnS and Zn(3)P(2) over the whole composition range of 0 < x < 1 was investigated by calculating the Gibbs free energy of mixing Delta(M)G for different values of x. A miscibility gap was found at both ends of the composition range and compared with experimental data.     

New electroluminescent materials based on chelate zinc complexes

Three new chelate zinc complexes with azomethine groups characterized by luminescence in the visible spectral region were synthesized: bis(N-(2-oxybenzylidene)cyclohexylamine)zinc, bis(N-(2-oxybenzylidene)-4-tert-butylaniline)zinc, and N,N′-bis(oxybenzylidene)-1,2-phenylenediaminezinc. Their spectral properties were studied. Based on these complexes, we prepared electroluminescence devices giving an intense emission in the blue, green, and red spectral regions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2056–2059, October, 2004.     

Synthesis,crystal structure,and electroluminescent properties of zinc and cadmium tetradentate azomethine complexes

Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetradentate Schiff bases (H₂L¹ and H₂L²) resulting from condensation of 2-tosylaminobenzaldehyde with 3,6-dioxa-1,8-octanediamine or 4,9-dioxa-1,12-dodecanediamine were performed. The structure, composition, and properties of the complexes were studied by elemental analysis, IR, ¹H NMR, and UV spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction. The zinc(II) and cadmium(II) complexes luminesce in a DMF solution in the blue spectral region (λ_PL = 425–433 nm), the photoluminescence quantum yield φ being 0.25–0.30. Multilayer zinc(II)- and cadmium(II)-based electroluminescent structures with green-blue emission of the exciplex nature were fabricated.     

Effect of surface modification of montmorillonite on the properties of rigid polyurethane foam composites

<正>This study investigated the influence of various organically modified montmorillonites(organoclays) on the structure and properties of rigid polyurethane foam(RPUF) nanocomposites.The organoclays were modified with cetyltrimethyl ammonium bromide(CTAB),methyl tallow bis(2-hydroxyethyl) quaternary ammonium chloride (MT2ETOH) and tris(hydroxymethyl)aminomethane(THMA) and denoted as CMMT,Cloisite 30B and OMMT, respectively.MT2ETOH and THMA contain hydroxyl groups,while THMA does not have long aliphatic tail in its molecule. X-ray diffraction and transmission electron microscopy show that OMMT and Cloisite 30B can be partially exfoliated in the RPUF nanocomposites because their intercalating agents MT2ETOH and THMA can react with isocyanate.However, CMMT modified with nonreactive CTAB is mainly intercalated in the RPUF matrices.At a relatively low filler content,the RPUF/CMMT composite foam has a higher specific compressive strength(the ratio of compressive strength against the apparent density of the foams),while at relatively high filler contents,RPUF/Cloisite 30B and RPUF/OMMT composites have higher specific compressive strengths,higher modulus and more uniform pore size than the RPUF/CMMT composite.     

Buffer-induced changes of purple membrane surface electric properties: an electro-optical study

Buffer-induced alteration of the purple membrane electric dipole moments and electrokinetic charge was studied by electric light scattering and microelectrophoresis. The permanent dipole moment and electrophoretic mobility of purple membranes change in opposite direction in presence of 'P'- and 'N'-type buffer molecules, shown to produce 'positive' and 'negative' additional components to the bR light-induced charge displacement current. It is concluded that the two types buffer molecules distribute differently on the membrane surfaces, depending on their protonation state, as a result of different interaction with the membrane cytoplasmic and extracellular surfaces.     

Structure and properties of nanocomposites based on zinc sulfide and poly(vinylidene fluoride)

The structure and properties of nanocomposites based on zinc sulfide and poly(vinylidene fluoride) were studied. The nanocomposite material was prepared by the matrix isolation technique: ZnS nanoparticles are formed by chemical reactions in a poly(vinylidene fluoride) powder of particle size 0.5–1.0 μm.     

Effect of surface modification of montmorillonite on the properties of aromatic polyamide/clay nanocomposites

The surface modification of montmorillonite clay was carried out through ion‐ exchange reaction using p‐phenylenediamine as a modifier. This modified clay was employed to prepare aromatic polyamide/organoclay nanocomposite materials. The dispersion behavior of clay was examined in the polyamide matrix. Polyamide chains were synthesized from 4‐aminophenyl sulfone and isophthaloyl chloride (IPC) in dimethylacetamide. These amide chains were suitably end‐capped with carbonyl chloride end groups to interact chemically with modified montmorillonite clay. The resulting nanocomposite films containing 2–20 wt% of organoclay were characterized by TEM, X‐ray diffraction (XRD), thin‐film tensile testing; thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and water absorption measurements. Mechanical testing revealed that modulus and strength improved up to 6 wt% organoclay loading while elongation and toughness of nanocomposites decreased with the addition of clay content in the matrix. Thermal decomposition temperatures of the nanocomposites were in the range 225–450 °C. These nanocomposites expressed increase in the glass‐transition temperature values relative to pure polyamide describing interfacial interactions among the phases. The percent water uptake of these composites reduced upon the addition of modified layered silicate depicting improved barrier properties. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of enantiomeric excess on thermotropic and electro-optical properties of ferroelectric sulphinate liquid crystals

The liquid crystalline behaviour and the electro-optical properties of mixtures of two pure ferroelectric enantiomers are studied as a function of the enantiomeric excess and compared with those of the corresponding racemate. It appears clearly that, depending upon the value of the enantiomeric excess, distinct thermotropic sequences are observed. The transition temperatures change significantly, and an additional SmB phase is observed for the racemate and for the mixtures of neighbouring concentrations. Moreover, the variation of the spontaneous polarization as a function of the enantiomeric excess is found to be strongly nonlinear. All these experimental observations show unambiguously that the thermotropic behaviour, the polar order, and consequently all the related electro-optical properties of the ferroelectric liquid crystal materials studied in the present work depend significantly upon the optical purity of the materials.     

Synthesis and electroluminescent properties of naphthalimide derivatives

Naphthalimide derivatives, N-ethyl-4-acetylamino-l ,8-naphthalimide (EAAN) and polymer with N-propyl-4-acetylamino-l,8-naphthalimide (PAAN) side-chain (P-PAAN) were successfully synthesized. Electroluminescent devices of ITO/PVK(120nm)/EAAN(50nm)/Al(150nm) (Ⅰ) and ITO/PVK P-PAAN( 10:1) (50nm)/Al(150nm) (Ⅱ) constructed with EAAN and P-PAAN as the emitting layer were investigated, whereas the single-layer devices of ITO/EAAN or P-PAAN(50nm)/Al(l50nm) (Ⅲ) were not observed to have any e-mission light. The emission results revealed that the exciton recombination formed by positive and negative charge carriers injected from electrodes of devices Ⅰ and Ⅱ was much more balanced than that of devices Ⅲ, which implied that naphthalimide derivatives are a new type of electron-transporting materials with high performance. The electron-transporting properties of naphthalimide derivatives were also elucidated by investigation of the electroluminescent behaviors from both devices of ITO/PPV (80nm)/Al and ITO/P     

Effect of monomer concentration and functionality on electro-optical properties of polymer-stabilised optically isotropic liquid crystals

Optically isotropic nature can open a new type of high-performance liquid crystal (LC) displays. The main features emerge from the interaction between LC and polymer network at the interface. At this point, we investigated the influence of cross-linking monomer concentration and functionality on electro-optic properties of optically isotropic liquid crystal (OILC) obtained by polymerisation-induced phase separation method. Interestingly, we obtained a pore-like network structure constructed by highly interlinked polymer beads in acrylate monomers and achieved fast decay response time (0.6 ms). We found that the voltage-dependent hysteresis was mostly eliminated (~0.25%), and the contrast ratio was enhanced (1:1550) for high functional monomers. The result inspires a simple way to optimise the materials to fabricate a high-performance OILC device and it shows high-transparency, low-driving voltage, hysteresis-free and sub-millisecond response time.     

Effect of the structure of gelators on electro-optical properties of liquid crystal physical gels

Low molecular mass organic gelator (LMOG) as an important component of liquid crystal physical gel has a great influence on the electro-optical properties. In this paper, three analogues of amide gelator were synthesized and employed as LMOGs in nematic liquid crystal 5CB. Both hydrogen-bonding and pi-pi-stacking interactions in the gel phase were found to stabilize the self-assembled structure. It was observed that the morphology was highly dependent on the crystallinity of gelators, which was affected by the intensity of hydrogen bonding. The thicker fibril was obtained with higher crystallinity of LMOG, while the thinner fibril was obtained with lower crystallinity. Moreover, the electro-optical properties of liquid crystal physical gels were proposed to be related to the interaction between the fibrils and the liquid crystal molecules.     

Optical and magnetic properties of manganese-incorporated zinc sulfide nanorods synthesized by a solvothermal process

Manganese-incorporated ZnS (MnxZn1-xS) nanorods were synthesized by a simple solvothermal process. Synthesized nanorods were single crystalline. Manganese incorporation in the ZnS lattice induces a phase transformation from hexagonal wurtzite to cubic zinc blende structure. The diameter of the nanorods increased with the increase of Mn concentration. Intense orange luminescence at approximately 585 nm was observed for the nanorods. Six-line hyperfine splitting was observed in the EPR spectra for lower Mn concentrations, whereas broad Lorentzian-shaped EPR spectra were obtained for higher Mn concentrations because of the Mn-Mn cluster formation at higher Mn concentrations.