ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymerization. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Steric interactions in a model multimembrane system: A synchrotron x-ray study.

Abstract: We report a high-resolution x-ray study of a model multilayer fluid membrane system in the lyotropic L/sub ..cap alpha../ phase of a quaternary microemulsion system. The structure factor exhibits power-law behavior characteristic of a Landau-Peierls system. As a function of intermembrane distance 3.8 nmless than or equal todless than or equal to16.3 nm, the exponent eta(d) which describes the algebraic decay of layer correlations is predicted by the model of Helfrich where entropic steric repulsions dominate intermembrane interactions.

Model for force fluctuations in bead packs.

Abstract: We study theoretically the complex network of forces that is responsible for the static structure and properties of granular materials. We present detailed calculations for a model in which the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead of the pile. We compare our results for the force distribution function for this model, including exact results for certain contact angle probability distributions, with numerical simulations of force distributions in random sphere packings. This model reproduces many aspects of the force distribution observed both in experiment and in numerical simulations of sphere packings. Our model is closely related to some that have been studied in the context of self-organized criticality. We present evidence that in the force distribution context, "critical" power-law force distributions occur only when a parameter (hidden in other interpretations) is tuned. Our numerical, mean field, and exact results all indicate that for almost all contact distributions the distribution of forces decays exponentially at large forces.

Aluminum-free monocyclopentadienyl metallocene catalysts for olefin polymerization

Abstract: The invention is a catalyst system including a Group IV-B transition metal component and an activator component which may be employed to polymerize olefins to produce a high molecular weight polymer. The Group IV-B transition metal component contains a single cyclopentadienyl ligand and a single heteroatom ligand, which ligands may be bridged one to another; the activator component comprises a cation, which may be a Bronsted acid capable of donating a proton (hereafter denoted as L'-H wherein L' is a neutral Lewis base and H is hydrogen), and a compatible noncoordinating anion.

On the relationship among three theories of relaxation in disordered systems.

Abstract: Empirical evidence has accumulated showing the wide occurrence of a stretched-exponential relaxation decay law for many diverse condensed-matter systems. Several theories based on different physical mechanisms have been successful in deriving the stretched-exponential decay law in a natural way. Three of these theories, the direct-transfer model, the hierarchically constrained dynamics model, and the defect-diffusion model are shown here to have an underlying common mathematical structure.

Structure of three-component microemulsions in the critical region determined by small-angle neutron scattering

Abstract: The intensity distribution of the critical scattering from sodium di-2-ethylhexylsulfosuccinate $\mathrm{AOT}\ensuremath{-}{\mathrm{D}}_{2}\mathrm{O}\ensuremath{-}n$-alkane water-in-oil (W/O) microemulsions has been measured over an extensive range of droplet volume fractions (3-30 vol%) and temperatures (22 to 43\ifmmode^\circ\else\textdegree\fi{}C) in the critical region. The water/surfactant molar ratio of the microemulsion was kept at a constant value of 40.8, for which previous experiments on the temperature variation have been well documented. A structural model of W/O microemulsions based on well-defined surfactant-coated water droplets is firmly established up to a volume fraction of about 20 vol% for all temperatures studied. Data analysis assumes that the cloud points and subsequent phase separation are caused by concentration fluctuations of polydisperse droplets. The major conclusions drawn from the analysis are as follows. (1) The order parameter of the critical phenomenon can be taken to be the volume fraction of the dispersed droplets. (2) The size and polydispersity of the droplets remain essentially constant in the vicinity of the critical point (for a fixed water/surfactant ratio). (3) The critical phenomenon is driven by an increased attraction between the droplets as the critical point is approached. (4) The critical point can be approached by either raising the temperature at fixed volume fraction or by varying the carbon number of the oil solvent at fixed volume fraction and temperature. (5) The nature of the droplets does not change upon a phase separation into two coexisting microemulsions. The data also gives some evidence that the droplet picture of the microemulsion breaks down at sufficiently high concentrations of water and surfactant.