Showing papers by "ExxonMobil published in 1985"

Limits of the Fractal Dimension for Irreversible Kinetic Aggregation of Gold Colloids

Abstract: We show that there are two regimes of irreversible, kinetic aggregation of aqueous colloids, determined by the short-range interparticle potential, through its control of the sticking probability upon approach of two particles. Each regime has different rate-limiting physics, aggregation dynamics, and cluster-mass distributions, and results in clusters with different fractal dimensions. These results set limits on the fractal dimension, ${d}_{f}$, for gold aggregates of $1.75l~{d}_{f}l~2.05$ (\ifmmode\pm\else\textpm\fi{}0.05).

Correspondence between electron binding energy and chemisorption reactivity of iron clusters.

Abstract: New experiments in a fast-flow reactor have uncovered a strong correlation between the reactivity of free iron clusters and cluster ionization thresholds: Clusters with low thresholds efficiently add molecular hydrogen, and the relative rates of this reaction closely follow variations in cluster-electron binding energy. This correspondence can be understood in terms of a requirement for metal-to-hydrogen charge transfer in the activation of the ${\mathrm{H}}_{2}$ bond.

Magnetic behavior of free-iron and iron oxide clusters.

Abstract: We report the first measurement of the magnetic properties of isolated iron-atom clusters ranging in size from 2 to 17 atoms as well as the magnetic behavior of the monoxides and dioxides of (2-7)-atom iron clusters. Production of metal clusters is initiated by laser vaporization of an iron rod inside the throat of a high-pressure pulsed nozzle. The neutral metal cluster beam passes through a Stern-Gerlach magnet and the deflected beam is detected by spatially resolved time-of-flight photoionization mass spectrometry. From our analysis we conclude that the spin per atom of iron clusters is at least that of bulk iron, suggesting these small clusters are the precursors to bulk ferromagnetic iron.

Cross-linking in shear-thickening ionomers

Abstract: Statistique des associations a l'equilibre, de l'association en ecoulement. Influence de l'etirage sur la reticulation et donc sur la viscosite

High‐temperature mutual solubilities of hydrocarbons and water. Part II: Ethylbenzene, ethylcyclohexane, and n‐octane

Abstract: In Part I (Tsonopoulos and Wilson, 1983), the mutual solubilities of three C6 hydrocarbons (benzene, cyclohexane, n-hexane) and water were experimentally investigated and, together with critically selected literature data, were correlated up to the three-phase critical end point. The present paper extends this analysis to the mutual solubilities of three C8 hydrocarbons (ethylbenzene, ethylcyclohexane, n-octane) and water, which have been measured at the three-phase equilibrium pressure up to the critical temperatures (568, 561 and 539 K, respectively). A thermodynamic analysis of these new measurements and of available literature data has been performed up to the three-phase critical end point. Information is also provided on vapor-phase equilibrium compositions. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility and volatility of water in hydrocarbons has been successfully correlated with several modifications of the Redlich-Kwong equation of state.

Percolation in interacting colloids.

Abstract: The percolation behavior of spherical particles with attractive interactions is studied with use of Monte Carlo simulations. These systems differ from lattice Ising systems, which have been previously analyzed, in the necessity to define a shell parameter \ensuremath{\delta} to specify a connected cluster. For small values of \ensuremath{\delta}, correlations due to the attractive interactions drastically lower the percolation threshold in the vicinity of the gas-liquid critical point. For larger values of \ensuremath{\delta}, these shifts are smaller, but the effects of long-range correlations show up as enhanced finite-size effects. The simulation results are discussed in the light of recent experiments which measure the temperature and concentration dependence of the conductivity in interacting microemulsions.

Polymerization catalyst, production and use

Abstract: of the Disclosure Ethylene and alpha-olefins are homopolymerized or copolymerized with another olefin monomer in the presence of a catalyst system comprising an organo metal cocatalyst and a treated titanium-containing catalyst component, said titanium-containing catalyst component being obtained by reacting together a porous particulate material, an organic magnesium compound, an oxygen containing compound, a halogen, interhalogen compound or halosilane and titanium tetrachloride

Dynamically cured thermoplastic olefin polymers

Abstract: Soft, resilient thermoplastic compositions with good physical strength useful as molded parts including hoses, seals and gaskets which exhibit good flow and good surface characteristics in injection molded parts. The compositions comprise ethylene copolymer resin (e.g., ethylene vinyl acetate), halogenated butyl rubber and polychloroprene wherein the rubbers have been dynamically vulcanized to a fully cured state in the presence of the ethylene copolymer resin.

A generalized differential effective medium theory

Abstract: A generalization of the Differential Effective Medium approximation (DEM) is discussed. The new scheme is applied to the estimation of the effective permittivity of a two phase dielectric composite. Ordinary DEM corresponds to a realizable microgeometry in which the composite is built up incrementally through a process of homogenization, with one phase always in dilute suspension and the other phase associated with the percolating backbone. The generalization of DEM assumes a third phase which acts as a backbone. The other two phases are progressively added to the backbone such that each addition is in an effectively homogeneous medium. A canonical ordinary differential equation is derived which describes the change in material properties as a function of the volume concentration φ of the added phases in the composite. As φ→ 1, the Effective Medium Approximation (EMA) is obtained. For φ

Molecular Weight and Association of Asphaltenes: a Critical Review

Abstract: The determination of asphaltene molecular weights is complicated by the tendency of asphaltene molecules to associate with each other and with other petroleum constituents, and reported molecular weights vary from 900 to 300 000. This paper reviews the methods (vapor pressure osmometry, size exclusion chromatography, ultrafiltration, ultracentrifugation, viscosity, small angle X-ray scattering, infrared spectroscopy, solubilization, and interfacial tension) that have been used to estimate asphaltene molecular weights and to probe association phenomena. It is concluded that asphaltene fractions from typical crudes have a number average molecular weight of 1 200-2 700 and a molecular weight range of 1,000-10,000 or higher. Intermolecular association phenomena are primarily responsible for observed molecular weights up to and in excess of 100,000 but detailed mechanisms of the intermolecular associations are not well understood. Certain observations suggest that asphaltene molecules are associated in reversedmicelles and that asphaltenes interact selectively with resins although the evidence on these points is subject to alternate interpretations. H-bond interactions between asphaltenes and resins have been demonstrated.

Free iron clusters react readily with O2 and H2S but are inert toward methane

Abstract: Donnees de resultats representant les reactivites reelles a basse temperature des agregats de fer libre, avec addition moleculaire d'O 2 (par exemple, Fe x O 2 pour 2≤x≤15) et formation de sulfures deshydrogenes (Fe x S) en tant que processus chimique primaire. Dans le cas du metane, on n'observe pas de reactions

Orientation of surfactant molecules at a liquid-air interface measured by optical second-harmonic generation

Abstract: . ' The average molecular orientation of a monolayer of sodium~dodecylnapthalene-sulfonate on a water-air interface has been determined by use of optical second-harmonic generation. The molecular orientation is shown to vary smoothly with increasing surface density of the molecules. Insoluble molecular monolayers at gas-liquid or li which is responsible for the SHG at an interface gen­ erally reflects the properties of the surface layer. If X 1'> arises mainly from a monolayer of molecular adsorbates, and takes the form (I)

Percolation in an oil-continuous microemulsion.

Abstract: Static and dynamic scaling behaviors of electrical conductivity and dielectric constant are obtained near the percolation transition in an oil-continuous microemulsion. Conductivity data are in agreement with a dynamic percolation picture and inconsistent with the static percolation expected from a bicontinuous structure. The dielectric constant, on the other hand, is found to be insensitive to the dynamical process.

Concentration profile of a dissolved polymer near the air-liquid interface: X-ray fluorescence study.

Abstract: The x-ray fluorescence, at the near-total external reflection configuration, was employed to study the concentration profile of a dissolved polymer near the liquid-gas interface. The determine experimental concentration profile conformed with a hyperbolic cotangent squared dependence with a concentration excess ratio of about 100:1 of the surface relative to the bulk. This experiment presents of first direct measurement of that kind at the air-liquid interface and demonstrates the effectiveness of this new method to study nondestructively interface structures on the scale of tens to hundreds of angstroms. 17 references, 3 figures.

Continuum percolation of rods.

Abstract: We determine the aspect-ratio dependence of the critical percolation threshold for various systems of rods. An exact expansion, due to Coniglio et al., tests the conjecture that the threshold is proportional to the inverse of the expected excluded volume. We confirm the conjecture, and show that the proportionality becomes equality, for isotropic rods in three dimensions, in the slender-rod limit. In this limit, the critical region in which nonclassical exponents are valid vanishes.

Effective-medium theories for two-phase dielectric media

Abstract: Two different effective‐medium theories for two‐phase dielectric composites are considered. They are the effective medium approximation (EMA) and the differential effective medium approximation (DEM). Both theories correspond to realizable microgeometries in which the composite is built up incrementally through a process of homogenization. The grains are assumed to be similar ellipsoids randomly oriented, for which the microgeometry of EMA is symmetric. The microgeometry of DEM is always unsymmetric in that one phase acts as a backbone. It is shown that both EMA and DEM give effective dielectric constants that satisfy the Hashin–Shtrikman bounds. A new realization of the Hashin–Shtrikman bounds is presented in terms of DEM. The general solution to the DEM equation is obtained and the percolation properties of both theories are considered. EMA always has a percolation threshold, unless the grains are needle shaped. In contrast, DEM with the conductor as backbone always percolates. However, the threshold in EMA can be avoided by allowing the grain shape to vary with volume fraction. The grains must become needlelike as the conducting phase vanishes in order to maintain a finite conductivity. Specifically, the grain‐shape history for which EMA reproduces DEM is found. The grain shapes are oblate for low‐volume fractions of insulator. As the volume fraction increases, the shape does not vary much, until at some critical volume fraction there is a discontinuous transition in grain shape from oblate to prolate. In general, it is not always possible to map DEM onto an equivalent EMA, and even when it is, the mapping is not preserved under the interchange of the two phases. This is because DEM is inherently unsymmetric between the two phases.

Low nox premix burner

Abstract: The invention relates to an improved premix burner and a method of its operation for combustion with a minimum of NO x emissions. The improvement is achieved by combining staged combustion with a premix burner in a manner such that mixing of the secondary air with the flame is delayed.

Viscosity index improver - dispersant additive useful in oil compositions

Abstract: Hydrocarbon polymers such as ethylene copolymers may be reacted with unsaturated nitrogen-containing monomers or unsaturated carboxylic acids in the presence of a free radical catalyst such as a peroxide or azo free radical initiator and a chain stopping agent, e.g. a mercaptan to inhibit excessive cross-linking and branching. The copolymer grafted directly with the nitrogen-containing monomers may be utilized as an additive for oil and fuel compositions, particularly lubricating oil compositions as a V.I.-dispersant additive. The polymer reacted with carboxylic acid may be further reacted with amines, polyols, amino-alcohols, etc. to also form a V.I.-dispersant additive.