Preparation of mesoporous cadmium sulfide nanoparticles with moderate pore size

The preparation of cadmium sulfide nanoparticles that have a moderate pore size is reported. This preparation method involves a hydrothermal process that produces a precursor mixture and a following acid treatment of the precursor to get the porous material. The majority of the particles have a pore size close to 20 nm, which complements and fills in the gap between the existing cadmium sulfide materials, which usually have a pore size either less than 10 nm or are well above 100 nm.     

Thermodynamic properties of DCl in D2O solution from 5 to 50°C

The themodynamic properties of solutions of deuterium chloride (DCl) in deuterium oxide (D₂O) have been determined from emf measurements of the electrochemical cell without transference from 5 to 50°C, and from 0.002 to 1.0 mol-kg^–1. The standard potential of the silver/silver chloride electrode relative to the platinum/deuterium electrode has been determined. An equation for the Gibbs energy as a function of temperature has been derived from which the enthalpy, entropy, and heat capacity have been computed. Equations for the activity coefficient and the osmotic coefficient of DCl in D₂O have been developed. The excess Gibbs energy of the solution and the excess partial molar free energy as a function of temperature have been calculated, from which the other excess thermodynamic properties have been computed. The values for the heat capacity and the apparent molar heat capacity have been compared with calorimetric data in the literature. The relative partial molar enthalpy has been calculated. The solvent isotope effect on the excess thermodynamic functions is discussed.     

Synthesis of nanostructured electrocatalysts based on magnetron ion sputtering

Nanostructured platinum catalysts for electrochemical systems with proton-exchange membranes (PEMs) have been synthesized by magnetron ion sputtering on a carbon support. The design of the powder support stirrer has been optimized to ensure uniform surface coverage with platinum metal nanoparticles. The deposition parameters (discharge power, deposition time, and bias voltage) that make it possible to obtain electrocatalysts with a large specific surface area (up to 44 m²/g) have been determined. The resulting catalysts have been studied by transmission electron microscopy and X-ray diffraction. The samples with platinum particles 3 to 4 nm in size uniformly distributed over the carbon surface and forming a single phase exhibit the greatest efficiency. The electrodes based on the synthesized electrocatalysts have been tested in a liquid electrolyte and as a component of a fuel cell and PEM water electrolyzer. The voltage across the fuel cell with the synthesized Pt/C electrocatalyst (44 m²/g) at a current density of 1 A/cm² is as high as 0.55 V, which corresponds to a specific power of 550 mW/cm². Qualitative correlations between the parameters of the synthesized catalysts and the deposition conditions have been established.     

C3H4: Theoretical study of structures and stabilities of isomers

The various isomers including stable structures, carbenes, and diradicals on the C₃H₄ surface have been investigated. The two carbenes propenylidene and cyclopropylidene have been found to have singlet ground states. Vinylmethylene is predicted to have a triplet ground state with a planar diradical type of structure. The syn and anti forms of this state are degenerate. This is in agreement with the observation of two triplet states in the electron spin resonance (ESR ) spectra. The π electrons are found to be delocalized over the three carbons. The singlet diradical structures are found to be more stable than the carbene structures, which retain the CH₂ (DOUBLE BOND) CH allylic structures. The orbital compositions of the frontier orbitals of all systems have been determined to examine the nature of these orbitals. © 1996 John Wiley & Sons, Inc.     

Non-symmetrical discotic liquid crystalline dimers: molecular design,synthesis and mesomorphic properties‡

The synthesis and mesomorphic properties of novel non-symmetrical discotic dimers have been investigated. Dimers have been prepared by the combination of electron-deficient (n-type) anthraquinone and electron-rich (p-type) triphenylene discotic monomers. The mesophases have been characterised using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. Most of the dimers have been shown to exhibit a rectangular columnar mesophase and one has a nematic columnar mesophase also. Charge transfer behaviour has been studied by UV–Vis spectroscopy.     

Interaction between sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) investigated with forward and reverse component addition protocols employing tensiometric, conductometric, microcalorimetric, electrokinetic, and DLS techniques

The interaction between polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) after the procedure of addition of the surfactant to polymer and the reverse procedure of addition of polymer to SDS micelles has been studied by tensiometric, conductometric, and microcalorimetric methods. The results have been analyzed and correlated with reference to SDS interfacial adsorption, association, and binding to PVP. Two aggregation states of SDS in presence of PVP have been found. The enthalpies of formation of SDS aggregates/micelles and their binding to the polymer have been evaluated. The interaction of PVP with SDS at concentrations below its critical micellar concentration (CMC) and above have evidenced distinctions. The forward addition protocol (FAP, SDS addition to PVP) and reverse addition protocol (RAP, PVP addition to SDS) have shown similarities and differences. Electrokinetic measurements have evidenced the interacted (SDS–PVP) colloidal products to possess negative zeta potential in the range of −39 to −65 mV. The hydrodynamic diameters of the PVP–SDS dispersion obtained from DLS measurements have ranged between 60 and 160 nm. Both zeta potential and hydrodynamic diameter have depended on [SDS] showing a maximum for the former at twice the critical micellar concentration of SDS.     

Heat capacities and thermodynamic functions of d-ribose and d-mannose

The heat capacities of d-ribose and d-mannose have been studied over the temperature range from 1.9 to 440 K for the first time using a combination of Quantum Design Physical Property Measurement System and a differential scanning calorimeter. The purity, crystal phase and thermal stability of these two compounds have been characterized using HPLC, XRD and TG–DTA techniques, respectively. The heat capacities of d-Mannose have been found to be larger than those of d-ribose due to its larger molecular weight, and the solid–liquid transition due to the sample melting has also been detected in the heat capacity curve. The heat capacities of these two compounds have been fitted to a series of theoretical models and empirical equations in the entire experimental temperature region, and the corresponding thermodynamic functions have been derived based on the curve fitting in the temperature range from 0 to 440 K. Moreover, the phase transition enthalpy and melting temperature of these two compounds have also been determined from the heat flows obtained in DSC measurements.

     

A systematic approach to the AA′BB′, AA′BB′MX and derived systems in nuclear magnetic resonance

The AA′BB′ and AA′BB′MX nuclear magnetic resonance spin systems for I = ½ nuclei have been analysed. Expressions for the transition frequencies and intensities have been obtained which have the maximum accuracy consistent with practicable use. The analyses have been applied respectively to a hypothetical AA′BB′ nuclear spin system and to the two molecules para- fluoro-phenyldichlorophosphine and tris-para-fluorophenylphosphine. Inconsistencies in earlier treatments of the AA′BB′ system have been clarified.     

Phase equilibria in the Tl-TlBr-Te system and thermodynamic properties of the compound Tl5Te2Br

The Tl-TlBr-Te composition region of the Tl-Te-Br phase diagram has been explored by DTA, X-ray diffraction, microhardness measurements, and electromotive force (emf) measurements relative to a thallium electrode in concentrations cells. The phase diagrams along a number of joins, the isothermal section at 400 K of the phase diagram, and a projection of the liquidus surface have been constructed. Extensive phase-separation areas, including a three-liquid-phase field in the Tl-TlBr-Tl₂Te subsystem, have been revealed. The homogeneity ranges and primary crystallization fields of phases have been mapped, and the coordinates of nonvariant and univariant equilibria in the T-x-y diagram have been determined. The standard thermodynamic functions of formation of the Tl₅Te₂Br compound and its standard entropy have been derived from emf data.     

Hafnia sol-gel films synthesized from HfCl4: Changes of structure and properties with the firing temperature

Thin sol-gel hafnia films have been synthesised from HfCl₄, the synthesis has revealed to be a simple route to fabrication of hafnia films with high transparency in the UV-visible range. The films have been fired at different temperatures in air up to 1000°C and have been characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Infrared absorption spectra of hafnia films have allowed to follow the formation of monoclinic crystalline phases together with XRD. Formation of monoclinic hafnia crystallites has been observed upon calcination at temperatures higher than 600°C, as shown by infrared spectroscopy and XRD. The optical transmission and the refractive index as a function of the temperature of firing have been characterized by UV-Visible spectroscopy and spectroscopic ellipsometry. The hafnia films, after firing at 600°C, had a refractive index of 1.92 with a thickness of around 70 nm.     

Self-avoiding walks in slits and slabs with interactive walls

Self-avoiding walk models of a polymer confined between two parallel attractive walls in two and three dimensions (slits and slabs, respectively) have recently had a revival of interest. They were first studied as simple models of steric stabilisation and sensitised flocculation in colloids. The revival has been catalysed by new exact solution techniques, that have allowed the solution of directed walk models in two dimensions in full generality, and by new Monte Carlo techniques that have allowed the simulation of the full parameter space in the three-dimensional slab model. Additionally, rigorous techniques applied to the slab problem have also yielded new results. The contributions to the study of this problem that have been recently added include a novel phase diagram for the “infinite-slab” (when the walls are a macroscopic distance apart but both walls may still “see” the polymer) the delineation of the repulsive and attractive regimes of the parameter space, and a conjectured scaling theory for the problem in general dimensions.     

Synthesis, reactivity ratios and characterization of hydroquinone promoted CT co-polymerization of styrene and methyl methacrylate in a room temperature ionic liquid

For the first time, charge transfer (CT) co-polymerization of styrene and methyl methacrylate, promoted by hydroquinone (HQ) at various feed compositions, has been achieved in a hydrophobic ionic liquid. The co-polymers have been characterized for thermal and molecular weight properties. The molecular weights obtained for the co-polymers made in ionic liquid were found to be slightly lower than the corresponding polymers synthesized in conventional solvent. The reactivity ratios of the co-polymers have been computed and compared with conventional CT polymerization. The reactivity ratios of Sty-MMA indicate that the co-polymerization has a tendency to alternate and to produce a higher styrene content in the co-polymers. The numerical values of the inverse of r₁ and r₂ indicate that both monomer radicals have a distinct cross propagation tendency.     

The substitution structure of nitroethylene

The ^15N- and ¹⁸O-species of nitroethylene have been assigned in natural abundance using microwave-microwave double resonance techniques. Additional transition frequencies have been measured for previously assigned isotopic species in order to have the same set of transitions for all species. The ground state rotational constants of nitroethylene, all eight mono-, three di- and two trisubstituted species have been used to determine the complete substitution structure. The results of the conventional Kraitchman-Constain method are compared to those of a least-squares method.     

Thermogravimetric studies on the reduction of hematite ore fines by a surrounding layer of coal or char fines: Part 1. Isothermal kinetic studies

Although there is a good deal of literature on the reduction of iron oxide by carbonaceous materials, it mostly covers systems where the oxide and reductant are thoroughly mixed. The present work concerns a system where the oxide and the reductant are not mixed.The kinetics of isothermal reduction of a central column of ore fines by a surrounding layer of coal fines have been studied by thermogravimetry. The course of reaction has been expressed in terms of a “degree of reaction” (f) defined as weight loss measured at a given time (t) with respect to the maximum possible weight loss. The kinetic data expressed in terms of f have been analysed using a kinetic law appropriate for diffusion-controlled processes and apparent activation energies have been calculated for reduction by coal and char. The results have been interpreted to identify carbon gasification as the rate-controlling step.     

Volumetric studies and thermodynamics of viscous flow of hydroxamic acids in acetone + water solvent at temperatures 303.15 and 313.15 K

Densities ρ and viscosities η of two hydroxamic acids, N-phenyl-2-chlorobenzo- and N-o-tolyl-4-chlorobenzo-, have been determined as a function of their concentration in aqueous acetone solution at temperatures 303.15 and 313.15 K. Apparent molar volumes, standard-state partial molar volumes and relative viscosities have been calculated. The viscosity data have been analyzed using Jones-Dole equation. The activation thermodynamic parameters of viscous flow have been evaluated using Feakins equation. These were obtained to throw light on the mechanism of viscous flow. Thermodynamic interactions in solutions have been studied in terms of a number of excess functions calculated from the experimental data. The effect of hydroxamic acid concentration and temperature on these parameters has been discussed. The results were interpreted in the light of solute-solvent interactions in aquo-organic media.     

Ab initio calculations on porphin

Ab initio SCF calculations are reported for the porphin molecule. The positions of the central protons have been optimized, and the equilibrium geometry is found to be a linear NH ? HN arrangement. The NH vibrational frequencies have been computed and are compared to experimentally measured quantities. Several low ionized states have also been studied in separate spin-restricted SCF calculations. The lowest state is found to have B_1u symmetry with an ionization potential of 8.0 eV.     

Cyclopolymerization of diastereomeric diepoxides

The meso- and d,l-diastereomers of o-bis(epoxyethyl)benzene have been synthesized and identified. The diastereomers were polymerized by a variety of catalysts to give a polymer which has mainly isochroman recurring units as a result of a cyclopolymerization mechanism. Some features of the polymerization with the triisobutylaluminum catalyst system have been studied. The rates of polymerization of the monomers and the transition temperatures of the resulting polymers have been determined. The results are explained on the basis of a controlled intramolecular propagation and a stereospecific polymerization.     

Uptake and release of surfactants from polyampholyte microgel particles

Polyampholyte microgel particles, containing both methacrylic acid and 2-(dimethylamino) ethyl methacrylate (a weak base), in a mainly N-isopropyl acrylamide network, have been prepared by free-radical dispersion polymerisation. The swelling properties of the particles have been shown to be pH and temperature dependent and to exhibit a minimum in size at the iso-electric point. The uptake and release of cetylpyridinium chloride and Triton X-100, into and from, the polyampholyte microgel particles have been investigated as a function of pH. The absorbed amounts at different pH values have been related to various specific interactions between the surfactant and the microgel network.     

Modulation of the Physicochemical Properties of Donor–Spiro–Acceptor Derivatives through Donor Unit Planarisation: Phenylacridine versus Indoloacridine—New Hosts for Green and Blue Phosphorescent Organic Light‐Emitting Diodes (PhOLEDs)

This work reports a detailed structure–property relationship study of a series of efficient host materials based on the donor–spiro–acceptor (D‐spiro‐A) design for green and sky‐blue phosphorescent organic light‐emitting diodes (PhOLEDs). The electronic and physical effects of the indoloacridine (IA) fragment connected through a spiro bridge to different acceptor units, namely, fluorene, dioxothioxanthene or diazafluorene moiety, have been investigated in depth. The resulting host materials have been easily synthesised through short, efficient, low‐cost, and highly adaptable synthetic routes by using common intermediates. The dyes possess a very high triplet energy (E_T) and tuneable HOMO/LUMO levels, depending on the strength of the donor/acceptor combination. The peculiar electrochemical and optical properties of the IA moiety have been investigated though a fine comparison with their phenylacridine counterparts to study the influence of planarisation. Finally, these molecules have been incorporated as hosts in green and sky‐blue PhOLEDs. For the derivative SIA‐TXO₂ as a host, external quantum efficiencies as high as 23 and 14 % have been obtained for green and sky‐blue PhOLEDs, respectively.     

Concave cell design for FTIR measurements

Wedged and V-shaped cells have advantages on depressing strong absorption bands and keeping the photo windows wide open without absorption block.Alternatively,this work presents a concave cell design,which is constructed by a plano-convex CaF₂ lens in combination with a flat plate.Mathematical equations have been provided for data treatment with Matlab programs.The result indicates that the concave cell has advantages similar to the V-shaped cell.Reflection-absorption measurements of ethanol have been conducted on the cell in mid-IR region for demonstration.The spectrum obtained from the concave cell can easily be interpreted to regenerate its normal spectrum,which is fitting well with the spectrum taken in a conventional thin-layer cell.The concave cell is easier to construct and more convenient to operate,willing to have popular usages.