Swelling of polyethylene particles and its relation to sorption equilibria under gas‐phase polymerization conditions

The attempts to predict the swelling of semicrystalline polyolefins using equations of state have not been successful so far and the few conducted experimental investigations have been limited to a narrow range of samples and conditions. This article presents a systematic video‐microscopic study of the swelling induced in various grades of PE particles by the sorption of ethylene and co‐monomers (propylene, 1‐hexene) at condition relevant to gas‐phase polymerization. Based on experimental data for various PE densities, the swelling factor H was evaluated, which enables the prediction of PE swelling by ethylene. The swelling data were compared with the corresponding gravimetrically measured sorption isotherms. In the case of ethylene and propylene sorption, the swelling significantly influences the evaluation of sorption isotherms. Conversely, the effect of swelling was negligible for higher hydrocarbons. The observed impact of swelling on the sorption is discussed based on the evaluated partial molar volumes of penetrants. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45035.     

Using resonance Raman spectroscopy to examine vibrational barriers to electron transfer and electronic delocalization

A time-dependent approach to the interpretation of resonance Raman scattering intensities has been used to obtain quantitative vibrational mode displacement information from scattering intensities associated with charge-transfer excitation. The displacements and associated frequencies are the key parameters needed to understand Franck-Condon effects in electron-transfer kinetics, and to delineate in a mode-specific way the composition of vibrational reorganization energies. Application of the approach to a number of types of electron-transfer reactions is described, including symmetrical and unsymmetrical intervalence electron transfers in inorganic and organic redox systems, metal-to-ligand charge-transfer reactions, and interfacial electron-transfer reactions. Also described is how the approach can be used to elucidate mechanisms for valence delocalization in strongly interacting redox systems.     

Clustering in nanostructured carbon: Evidence of electron delocalization

The electronic properties of disordered carbon-based materials can be discussed in terms of the clustering of the sp² carbon phase and delocalization of the electron wave function. In smooth amorphous carbon thin films this results in a mixed phase material of conductive sp² clusters embedded in an electrically insulating sp³ matrix. The delocalization of the electron wave function associated with the sp² clusters is shown to play an important role in understanding many of the electronic and optical properties of the films. It is demonstrated that the extent of the electron delocalization and clustering can be estimated using magnetic resonance methods. Evidence for delocalization in a range of carbon-based materials such as diamond-like carbon thin films produced by chemical vapour deposition, nanostructured carbon produced by pulsed laser ablation and ultrananocrystalline diamond is presented.     

Salmonella in relation to agriculture

Some of the more extensive programs directed to the control of salmonellosis in domestic animals, which have been conducted by the U.S. Department of Agriculture, are identified. These have been singularly successful, insofar as the economics of production is concerned. However, they fall short of meeting the present market demand for food free from all of the 900–1,200 odd serotype species ofSalmonella considered potentially infectious for man. The increasing incidence of salmonellosis in man, and the identification of domestic animals as a major reservoir of various species ofSalmonella, has made it necessary to broaden the objective of existing programs, expand the research effort, and intensify testing schedules in many of the existing regulatory control programs. The activities of a special salmonella task force set up to coordinate research with the needs of the various regulatory agencies specifically concerned are reviewed. Data developed by the Animal Health Division in a market survey of feed and feed ingredients as carriers of salmonella are presented. The more pressing problems and the current programs within other Divisions are discussed, insofar as the findings to date may serve to identify future needs. Presented at the AOCS-AACC Joint Meeting, Washington, D.C., April, 1968.     

Chemical equilibria in methanol synthesis

The chemical equilibria of the methanol reaction and the water—gas shift reaction, starting from carbon monoxide, carbon dioxide and hydrogen, were studied in a fixed-bed catalytic reactor at P = 10–80 bar and T = 200–270°C. It was found that the chemical equilibria could be described very well by thermochemical data based on ideal gas behaviour in combination with a correction for the non-ideality of the gas mixture as predicted by the Soave—Redlich—Kwong equation of state. This correction for non-ideality results in significantly better agreement with experimental data than a correction based on the original Redlich—Kwong equation of state, the Peng—Robinson equation of state, the virial equation truncated after the second virial coefficient, Lewis and Randall's rule, or not correcting at all for non-ideality, thus assuming ideal gas behaviour.     

Probing the electronic delocalization in a cyclic pyrazine ruthenium cluster hexamer

[Ru₃O(CH₃COO)₆(pz)(CO)]₆ is a cyclic hexamer species encompassing six triangular ruthenium cluster centers bridged by pyrazine ligands. The electronic communication among the cluster units strongly depends on their oxidation states, and has been successfully probed by means of cyclic voltammetry and UV–vis spectroelectrochemistry.     

Vapour-liquid equilibria in associating solutions

Isobaric vapour—liquid equilibria data were measured for the binary mixtures of acetic acid—propionic acid and formic acid—propionic acid at 760 mm Hg. The data were tested against a new thermodynamic model which extends the one proposed by Marek in that it is suitable for the case of binary mixtures containing two associating species and takes into account hetero-dimerization in the vapour phase. The proposed model converts into that of Christian for the particular case of an ideal liquid solution. The model fits well the system acetic acid—propionic acid with regard to the thermodynamic consistency of the overall activity coefficients, but does not fit the second mixture so well, probably because higher degrees of polymerization have to be included in it.     

Prepreg aging in relation to tack

Thermoanalytical measurements and tack tests were both performed using a commercially available carbon fiber/epoxy prepreg system (Hercules 3501–6) to examine changes caused by aging as they affect handling and processability of thermosetting matrix-based composites. Combining these techniques, a relationship between prepreg bulk and surface characteristics in relation to aging was investigated. Isothermal kinetic studies at low temperatures showed maximum conversions (α_m) that increased with increasing cure temperatures. In addition, a linear relationship between glass transition temperatures (T_g) and conversions (α) was observed regardless of aging (or cure) temperatures. Energy of separation of prepreg stacks, which may be viewed as a measure of prepreg tack, showed a maximum value at a specific temperature. The maximum energy of separation was observed in the temperature range of 20–25°C above the glass transition temperature for a given sample. However, the maximum energy of separation values decreased with increasing aging times (or conversions), implying that prepreg tack was a viscoelastic property rather than a viscous property of the resin matrix in the prepreg.     

Magnetic field induced delocalization in multi-wall carbon nanotube-polystyrene composite at high fields

In well dispersed multi-wall carbon nanotube-polystyrene composite of 15 wt%, with room temperature conductivity of ∼5 S/cm and resistivity ratio [R_2 K/R_200 K] of ∼1.4, the temperature dependence of conductivity follows a power-law behavior. The conductivity increases with magnetic field for a wide range of temperature (2–200 K), and power-law fits to conductivity data show that localization length (ξ) increases with magnetic field, resulting in a large negative magnetoresistance (MR). At 50 T, the negative MR at 8 K is ∼13% and it shows a maximum at 90 K (∼25%). This unusually large negative MR indicates that the field is delocalizing the charge carriers even at higher temperatures, apart from the smaller weak localization contribution at T < 20 K. This field-induced delocalization mechanism of MR can provide insight into the intra and inter tube transport.     

Vapor-liquid equilibria in the argon-methane system

Vapor-liquid equilibrium compositions have been measured for the argon-methane system at 115.2°, 123.4° and 137.1°K, by means of a forced-recirculation apparatus. A modified Redlich-Kwong equation of state with the incorporation of a binary interaction constant has been successfully employed to represent the data. Liquid activity coefficients have been evaluated and correlated.     

Non-unique reaction equilibria in non-ideal systems

Illustrations are given of non-ideal solutions of chemically reactive substances which display more than one equilibrium state, i.e. more than one relative minimum of Gibbs free energy. Simple cases are pairs of minima in symmetric regular solutions and unsymmetric Margules and van Laar solutions of two isomers in reactive equilibrium. The accessibility of the absolute minimum is discussed. Implications are pointed out for the general problem of calculating equilibrium states in non-ideal reaction systems.     

Liquid-liquid-vapor equilibria in the nitrogen-methane-ethane system

Liquid-liquid-vapor equilibrium compositions were measured for the nitrogen-ethane binary and the nitrogen-methane-ethane ternary systems from –255° to –219.8°F and at pressures up to 591 psia. A forced-recirculation apparatus was employed for the determinations. Experimental results were interpreted and correlated. Optimum operating temperature for nitrogen separation has been suggested.     

Phase equilibria in polydisperse colloidal systems

Many materials containing colloids or polymers are polydisperse: they comprise particles with properties (such as diameter, charge, or polymer chain length) that depend continuously on one or several parameters. This effectively infinite number of distinguishable particle species makes the theoretical prediction of phase equilibria a highly non-trivial task. We give an overview of recent progress, focussing on the “moment free energy” method which reduces the problem to one involving only the densities of a finite number of quasi-species. Applications to isotropic–nematic phase equilibria of rod-like particles and to the phase behaviour of polydisperse hard spheres are described.     

Vapor-liquid equilibria in the methane-ethylene-ethane system

Vapor-liquid equilibrium compositions were measured for the methane-ethylene binary at — 156.1°, — 173.1° and — 193.1° F, the methane-ethane binary at — 173-1° F, and the methane-ethylene-ethane ternary at — 173.1° F and at pressure up to 330 p.s.i.a. A forced recirculation apparatus was employed for the determinations. Liquid activity coefficients, γ, were evaluated by means of a modified Redlich-Kwong equation of state incorporating with binary interaction constant and correlated by the Redlich-Kister equation. Equilibrium data for the ethylene-ethane binary system at — 173° F were predicted by the modified Redlich-Kwong equation of state for correlating the γ values of the methane-ethylene-ethane ternary system.