ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymer. 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..

H − T phase diagram for spin-glasses: An experimental study of Ag:Mn

Abstract: We present high-resolution SQUID (superconducting quantum interference device) measurements of the dc magnetization on two Ag:Mn samples containing 2.6 and 4.0 at.% Mn. We have measured in detail the temperature dependence of the magnetization on warming through the glass temperature, ${T}_{G}$, (i) after cooling to $Tl{T}_{G}$ in a near-zero field and then applying the measurement field, zero-field cooled, and (ii) after cooling to $Tl{T}_{G}$ in the measurement field. This has been done for fields $0.5\ensuremath{\le}H\ensuremath{\le}500$ Oe. The temperature derivative, $\frac{\mathrm{dM}(H,T)}{\mathrm{dT}}$, of the ZFC curve shows structure, allowing the identification of several characteristic temperatures associated with the paramagnetic to spin-glass transition in the presence of an external magnetic field. The temperature, ${T}_{B}$, where the crossover from a Curie-like to a nonlinear susceptibility occurs, behaves as $\ensuremath{\sim}{H}^{0.5\ifmmode\pm\else\textpm\fi{}0.1}$. Two further temperatures, $\overline{T}$ and ${T}_{P}$, where $\overline{T}l{T}_{P}l{T}_{G}^{0}(H\ensuremath{\rightarrow}0)$ are suggested as possible candidates for the theoretical-field-dependent transition temperature ${T}_{G}(H)$ given by ${1\ensuremath{-}[\frac{{T}_{G}(H)}{{T}_{G}^{0}}]}={\mathrm{Ah}}^{\frac{2}{3}}$ where $h=\frac{H}{J}=\frac{{g}_{{\ensuremath{\mu}}_{B}}H}{{k}_{B}{T}_{G}^{0}}$ and $A$ is of order unity. We find ${1\ensuremath{-}[\frac{\overline{T}(H)}{{T}_{G}^{0}}]}={\mathrm{Bh}}^{0.70\ifmmode\pm\else\textpm\fi{}0.05}$, but where $B$ is approximately ${(19)}^{2/3}$. However, the ${T}_{P}$ data are consistent with the theoretical prediction ($A\ensuremath{\simeq}1$) using no adjustable parameters, but the range of data is insufficient to enable an unambiguous verification of the theory. On the basis of recent theories, we suggest that the system entering the spin-glass phase at ${T}_{G}(H)$ should be marked experimentally by ${\ensuremath{\chi}}_{\mathrm{dc}}=\frac{M}{{H}_{\mathrm{static}}}g{\ensuremath{\chi}}_{\mathrm{ac}}(\ensuremath{ u},{H}_{\mathrm{osc}},{H}_{\mathrm{static}})$ where $M$ is the magnetization, ${H}_{\mathrm{static}}$ the magnitude of the dc field, ${H}_{\mathrm{osc}}$ the amplitude of the ac oscillating field, and $\ensuremath{ u}$ its frequency. This argument leads us to conclude that ${T}_{P}(H)$ should be taken as the experimental definition of ${T}_{G}(H)$.

A Comparison of Techniques for Measuring Yield Stresses

Abstract: Three techniques for measuring yield stresses are compared by performing parallel experiments on five model oil‐in‐water emulsions. The emulsions displayed yield stresses of 50–550 dynes/cm2. The three techniques involved: (1) measurements of rotation rate and stress in a concentric‐cylinder geometry, (2) measurement of torque and apparent shear rate in a parallel disk geometry at two different gap heights, and (3) measurement of rotation under constant applied stress in a vane geometry previously described by Boger. Emulsions are prone to slip at solid boundaries; therefore, methods to assess wall slip contributions for techniques (1) and (2) are developed. The vane device eliminates the possibility of slip. The measurements give comparable results. The techniques are compared with respect to: precision, ease of implementation, information obtained, and sample requirements.

Interfacial Sliding of Polymer Brushes: A Molecular Dynamics Simulation.

Abstract: Polymers end grafted to a surface have recently been shown to have an anomalously low effective friction coefficient ${\ensuremath{\mu}}_{b}$. To understand the origin of the observed reduction in friction, molecular dynamics simulations of polymers tethered at one end to a surface in a good solvent were carried out. As the surfaces are brought into contact, the normal force increases rapidly, while the shear force is found to be significantly smaller. For low shear velocity $v$, the surfaces slide past each other with no change in the chain's radius of gyration or the amount of interpenetration. In this regime the shear force increases linearly with $v$. For larger $v$, there is significant chain stretching and disentanglement.

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.