Quartz Microbalance Microcalorimetry: A new method for studying polymer-solvent thermodynamics

We have developed a sensitive method of determining enthalpy changes for gas-surface interactions: quartz microbalance microcalorimetry. We mount in an isoperibol environment both sample and reference combinations of a quartz crystal microbalance (QCM) in intimate thermal contact with a heat flow sensor. We coat the sample QCM with a thin (1 µm) polymer film. By exposing the film to ethanol vapor, we measure simultaneously the change in mass per unit area (to ±0.25 ng cm^–2) and the resulting heat flows (to ±50 nW) when the polymer adsorbs or desorbs ethanol. The molar enthalpies of sorption of ethanol vapor in Tecoflex, an aliphatic polyurethane elastomer, are _adsorptionH= –53±8 kJ mol^–1 and _desorptionH=52±3 kJ mol^–1.This revised version was published online in November 2005 with corrections to the Cover Date.     

A new method for studying crystallization of amorphous alloys

Experiments on the crystallization of amorphous Fe?Si?B alloys were carried out by thermogravimetric analysis (TG). This new method gives us some important information about the magnetic phase transformation of amorphous alloys, especially the magnetic volume change in crystallization beside the energy change obtained by the traditional DSC and DTA methods. Crystallization activation energies of Fe?Si?B amorphous alloy are calculated from both TG and DTA curves. The experiment also showed that the addition of Nb, Cu and Mo would influence the crystallization transition temperature of amorphous Fe?Si?B alloys greatly.     

A new cellular carbon support for catalysts: preparation and study of structure

Cellular carbon has been prepared by pyrolysis of a propane—butane mixture in a flow reactor at 700–1250 K. Its structural characteristics were studied by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and adsorption methods. It was shown that cell-type carbon possesses a unique structure in contrast to carbon composite “Sibunnit” and filamentous carbons and it may be a promising support for catalyst preparation.     

A new method for the preparation of peroxyacetic acid using solid superacid catalysts

A new method for the preparation of peroxyacetic acid from acetic acid and hydrogen peroxide in the presence of solid superacids as a catalyst under mild conditions has been proposed. The preparation of peroxyacetic acid could be carried out in a batchwise operation as well as in a flow-system operation. Nafion-H was found to be active and very stable catalyst for the preparation of peroxyacetic acid and to be regenerated without the loss of catalytic activity.     

A new microwave dielectric method for studying photoinitiated chain radical polymerization processes

Measurements of both real and imaginary parts of the dielectric constant at a fixed microwave frequency have been performed on n-butyl acrylate/poly(n-butyl acrylate) mixtures. The dielectric constant of the mixtures has been compared with that of neat n-butyl acrylate during UV photoinitiated polymerization. The values of the imaginary part of the dielectric constant thus obtained have allowed determination of the instantaneous monomer concentration and verified the kinetic equation for the photoinitiated polymerization process. The limits of validity of the method as well as its capability of providing detailed kinetic information are also discussed.     

Scintillation phase method: A new approach for studying surfactant behavior at liquid/liquid interface

Radiochemical approach for the investigation of partitioning and adsorption of surfactants at water-oil interfaces has been developed. The so-called “scintillation phase method” is based on the introduction of tritium labeled surfactant in an aqueous phase of the water-oil system followed by measuring radioactivity of the whole system. Partition coefficients and the value of adsorption at water-non-polar liquid interfaces of homologous series of alkyltrimethylammonium bromides (DTAB, TTAB and CTAB) have been experimentally determined by means of scintillation phase method. The influence of non-ionic surfactants on TTAB adsorption has also been studied.     

SERS: A new method for the study of electronic structure in ultrasmall particles

Earlier work suggested that surface enhanced Raman scattering arises from off-diagonal coupling of excitations in the molecule and substrate. Using a free-electron model for a metallic substrate, large enhancements are confirmed, and insight gained about the effects of (1) substrate size, (2) molecular location, (3) density of states, and (4) excitation wavelength. Structured SERS and anti-enhancements occur under suitable conditions.     

A new method for recycling asymmetric catalysts via formation of charge transfer complexes

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity.     

Laser vaporization: A versatile method for studying metal clusters

Vaporizing solid samples of metals and semiconductors with a YAG Laser is a method well suited for producing molecules and clusters of those materials. The clusters are examined by either laser-induced fluorescence (LIF) or mass spectroscopic methods. The technique is valuable for both gas phase and matrix studies. The method is described and some applications, studying either the structure of small metal molecules or their reactions, are reviewed, with emphasis on our recent results from the LIF studies of LiBe, Al₂ and the reaction of Al with oxygen, yielding A1₂O. For larger clusters, Ion Cyclotron Resonance is an extremely valuable method, as we demonstrate by its application to the reactions of small charged silicon clusters with strong oxidising agents.     

Electron microscopic study of the structure of nickel catalysts modified with heteropoly compounds

The state of the active phase on the surface of low-percentage nickel catalysts on carbon supports in the presence of new modifiers, mixed series 12 heteropoly compounds (HPC), was investigated. The presence of a modifier causes an increase in the dispersion of the nickel, formation of nickel-HPC associates on the surface of the support, and determines the high dispersion and thermal stability of the Ni particles in reducing medium. Modified nickel catalysts have higher selectivity for coal oils during liquid-phase hydrogenation of coal, and the process takes place with less gas formation.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2705–2711, December, 1990.     

A new method to reconstruct three-dimensional spatial distribution function from radial distribution function in solvation structure

Three-dimensional spatial distribution function (SDF) of solvent is a fundamental quantity for analysis of solvation. However, its calculation has been very limited because long computational time is required. We here developed a novel and robust method to construct approximated SDFs of solvent sites from radial distribution functions. In this method, the expansion of SDFs in real solid harmonics around atoms of solute leads to a linear equation, from which SDFs are evaluated with reasonable computational time. This method is applied to the analysis of the solvation structure of liquid water, as an example. The successful results clearly show that this method is very powerful to investigate solvation structure.     

A new method of preparing a rotating ring-disc electrode for the study of carbon supported catalysts

A new preparation method is described for the study of carbon supported electrodes, which are currently under investigation for fuel cell applications. The carbon is applied to the disc of a rotating ring—disc electrode (RRDE) through incorporation of the carbon particles ina polypyrrole film. Electron transport to the carbon is possible because the polypyrrole is electronically conducting; the high porosity of the film enables the diffusion of reactants into the pores of the catalyst. This new technique offers an easy and quick way of measuring both the activity and selectivity of carbonsupported catalysts.     

A new chemical system for studying pattern formation: bromate-hypophosphite-acetone-dual catalyst

A modified version of the short-lived BrO3(-)-H2PO2(-)-Mn(II)-N2 oscillator, the BrO3(-)-H2PO2(-)-acetone-dual catalyst system, where the catalyst pair can be Mn(II)-Ru(bpy)3SO4, or Mn(II)-ferroin, or Mn(II)-diphenylamine, shows long-lasting batch oscillations in the potential of a Pt electrode and in colour, accompanying periodic transitions between the oxidised and reduced forms of the catalysts. Experimental conditions for the oscillations are established. The origin of the batch oscillations and the role of the catalyst pair in the oscillatory behaviour are discussed. The new system is ideally suited to the study of waves and patterns in reaction-diffusion systems, since in addition to the longevity of its spatial behaviour in batch, it produces no gaseous or solid products and exhibits significant photosensitivity.     

预测烷烃密度的新方法: 基团键贡献法

根据分子结构的特点,通过用染色矩阵和邻接矩阵对分子结构进行矩阵化表征,发展了一种根据分子结构信息烷烃密度的新方法---基团键贡献法。该方法有机地将基团贡献法和化学键贡献法结合在一起,既考虑了分子中基团的特性,又考虑了基团之间的连接性(化学键),具有基团贡献法和化学键贡献法的特点。对658种烷烃的计算结果表明,密度预测值十分接近实验值,平均误差0.245%,进一步外推对聚乙烯、聚丙烯和聚1-丁烯等聚合物的密度进行预测,也取得了令人满意的结果。     

A new technique for studying gelation in polyesters

A new method for studying polymer network formation has been devised. Crosslinking reactions are carried out in a recording viscometer, which provides accurate determination of incipient gel points and also serves as a high-speed stirrer. The molten, nonstoichiometric mixtures are reacted to completion to eliminate the inaccuracies inherent in the determination of reaction extent and this, together with the use of esterification reactions with minimal side reactions, reduces many of the problems of previous methods. The experimental results for the reactions of simple model compounds are in very close agreement with Flory's network theory. A system containing crosslinking reagents with unequally reactive groups has also been considered and the accuracy of the method enables the reactivity ratios of the different groups to be calculated.