Permeability of an interfacial polymerized film in an oil/water emulsion. A spin label study

Summary This work has shown that the ESR technique is a convenient method for studying the permeability processes through an interface in an oil/water emulsion. We were able to determine the permeability of the film at the interface as a function of the level of cross-linked polymerisation. Comparing to our crude previous study (1), we see that the polymerisation reaction continues largely after the time necessary to stabilize the emulsion (=30 min). Using two spin labels of significantly different size, we obtain an estimation of the average size of the holes in the interfacial network at different steps of the polymerisation process. These results could have applications for selective permeability of cross-linked membranes.

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Zusammenfassung In der Arbeit wird gezeigt, daß die ESR-Technik zum Studium von Permeationsvorgängen durch Grenzflächen in Öl-Wasser-Emulsionen geeignet ist. Es gelang, die Permeabilität des Films an der Grenzfläche als Funktion des Quervernetzungsgrades zu bestimmen. Verglichen mit früheren Messungen zeigt es sich, daß die Polymerisationsreaktion wesentlich länger dauert als die Zeit, um die Emulsion zu stabilisieren. Durch Verwendung zweier Spin-Label mit stark unterschiedlicher Größe konnte die mittlere Größe der Löcher im Grenzflächennetzwerk bei verschiedenen Stufen der Polymerisationsreaktion abgeschätzt werden. Die Ergebnisse könnten zum Verständnis der selektiven Permeabilität durch quervernetzte Membranen Bedeutung haben.

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With 5 figures and 1 table

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Work partially supported by D.R.M.E. under contract No. 7534200.     

The elastic and bonding properties of the sulvanite compounds: A first-principles study by local and semi-local functionals

The elastic properties of the compound family of the sulvanite Cu₃TMX₄ (TM=V, Nb, Ta; X=S, Se) have been calculated using first-principles total energy calculations within the density functional theory along with the local density and the generalized gradient approximations. The calculated elastic properties are the bulk modulus (B), the elastic constants (c₁₁, c₁₂ and c₄₄), the Zener anisotropy factor (A), the isotropic shear modulus (G) and the Young modulus (E). By means of these quantities we have also computed other thermodynamic properties such as the average sound velocity (s) and the Debye temperature (Θ_D). The calculated values of the elastic properties led to the conclusion that these compounds are brittle and fragile. We have also calculated the electron localization function, which exhibits the bonding characteristics in these compounds, showing that the Cu-X bond as well as the TM-X bond have a covalent character, but there is also present some ionicity in these compounds due to the Cu-TMX₄ bond.     

Velocity autocorrelation function for the motion of long-chain molecules in the free draining limit

The thermal motion of a long-chain molecule dispersed in a solvent is examined in terms of the velocity autocorrelation, in a reference frame attached to a subunit of the chain.     

Modeling the angular capability of the ball joints in a complex mechanism with two degrees of mobility

The paper puts forward a complex linkage mechanism with two degrees of mobility and three kinematic loops, which is used for the guiding (suspension and steering) system of the vehicles. The geometric parameters and the coordinates frames that define the mechanical system are presented, as well as the specific kinematic functions. For this complex mechanical system, the angular capability of the ball (spherical) joints is defined by two angles. The equations for these angles have been determined by matrix algebra tools, considering the transformation matrices between the bodies reference frames. The diagrams of the angular capability of the ball joints, which are represented in angular coordinates, describe the form, orientation and size of the sockets from the spherical casings. Wears, shocks, functional locks or the compromising of the joint strength can occur if scarce sockets are implemented. The risk points, in which the angular parameters have maximum values, have been determined, the simulation being performed for a real system (vehicle).     

Experimental study of biogas combustion using a gas turbine configuration

The aim of the present work is to compare stability combustion domains, flame structures and dynamics between CH₄/air flames and a biogas/air flames (issued from waste methanisation) in a lean gas turbine premixed combustion conditions. Velocity profiles are obtained by Laser Doppler Anemometry measurements. CH* chemiluminescence measurements and temporal acquisition of chamber pressure are performed in order to describe flame structure and instabilities. Changes in flame structure and dynamics when fuel composition is varying are found to strongly depend on laminar flame speed. No clear correlation between the unstable flame and the reaction zone penetration in the corner recirculation can be found.     

Effects of size on the dynamics of dislocations in ice single crystals

Single crystals of ice subjected to primary creep in torsion exhibit a softening behavior: the plastic strain rate increases with time. In a cylindrical sample, the size of the radius affects this response. The smaller the radius of the sample becomes while keeping constant the average shear stress across a section, the softer the response. The size-dependent behavior is interpreted by using a field dislocation theory, in terms of the coupled dynamics of excess screw dislocations gliding in basal planes and statistical dislocations developed through cross slip occurring in prismatic planes. The differences in the results caused by sample height effects and variations in the initial dislocation microstructure are discussed.     

Elastic constitutive laws for incompatible crystalline media: the contributions of dislocations,disclinations and G-disclinations

Linear higher-grade higher-order elastic constitutive laws for compatible (defect-free) and incompatible (containing crystal line defects) media are presented. In the proposed model, the free energy density of a body subjected to elastic deformation under the action of surface tractions, moments or hyper-traction tensors (second-order tensors whose anti-symmetric part corresponds to moments) has contributions coming from the first two gradients of displacements. Thermodynamic considerations reveal that only the symmetric component of the gradient of elastic displacement, i.e., compatible elastic strain tensor, and the anti-symmetric component of the second gradient of elastic displacement, i.e., compatible third-order elastic curvature tensor, contribute to the free energy density during compatible deformation of the body. The line crystal defect contributions are accounted for by incorporating the incompatible components of elastic strains, curvatures and symmetric 2-distortions as state variables of the free energy density. In particular, the presence of generalized disclinations (G-disclinations) is acknowledged when the medium is subjected to surface hyper-traction tensors having a non-zero symmetric component along with surface-tractions on its boundary. Mechanical dissipation analysis provides for the coupling between the Cauchy stresses and third-order symmetric hyper-stresses. The free energy density and elastic laws for a defect-free and line crystal defected medium are proposed in a linear setting. In the special case of isotropy, the cross terms between elastic strains and curvatures contribute to the free energy density through a single elastic constant. More interestingly, the Cauchy and couple stresses are found to have contributions coming from both, elastic strains and curvatures.     

SILVER CHLORIDE MICROCRYSTALS SUSPENSIONS IN MICROEMULSION MEDIA

A study of the precipitation of silver chloride in a micro-emulsion medium is presented. Measurements of turbidity, X-ray diffraction and small angle scattering show, the rapid formation of small crystals, about 60 °A in diameter wliich show no further growth and aggregate only slowly ; the stabilization of these solid particle suspensions, of steric or electrostatic origin, is increased by six orders of magnitude in comparison with aqueous colloidal solutions