Investigation of Polymers by Inverse Gas Chromatography

This Perspective conveys to the general reader of <i>Macromolecules</i> the basic ideas and possibilities of inverse gas chromatography (IGC). This method which appeared about 50 years ago is now a versatile tool for investigation of the interactions of polymers with vapors and study of polymer properties. The focus of this Perspective is on the study of bulk sorption of low molecular weight compounds in polymers. The results of chromatographic determination of solubility coefficients and sorption isotherms as well as the diffusion coefficients of vapors in polymers are discussed. Special attention is paid to the thermodynamic properties of glassy polymers on the phenomena in the vicinity of the glass transition. Information on IGC as a probe method for the determination of free volume in polymers is also presented

Entry of magnetic flux into a magnetically shielded type-II superconductor filament

In the framework of the London approximation the magnetic flux penetration into a type-II superconductor filament surrounded by a soft-magnet sheath and exposed to a transverse external magnetic field is studied. The lower transverse critical field as well as the critical field and the critical current of the first vortex nucleation at the superconductor/magnet interface are calculated on the basis of an exact solution for a vortex of arbitrary plane configuration. The Bean-Livingston barrier against the vortex nucleation is shown to strongly depend on the magnet sheath parameters.Comment: 15 pages, 6 figures, RevTeX4; in print in Phys. Rev.

Correlation of Gas Permeability and Diffusivity with Selectivity: Orientations of the Clouds of the Data Points and the Effects of Temperature

For an extended data set for amorphous glassy polymers, the pair correlations <i>P</i>_<i>i</i>–<i>P</i>_<i>j</i> fulfill with very good accuracy (<i>R</i>² about 0.9 or higher) where <i>P</i>_<i>j</i> and <i>P</i>_<i>j</i> are the permeability coefficients of the gases M_<i>i</i> and M_<i>j</i> in the same polymers. This allowed us to determine the orientation (medians) of the clouds of the data points on the correlations log <i>P</i>_<i>i</i> versus α_<i>ij</i> = <i>P</i>_<i>i</i>/<i>P</i>_<i>j</i>. It was shown that for various gas pairs the slopes of these medians are negative and increase by absolute value when the ratio of kinetic diameters of the penetrants increases. For the first time a similar analysis was carried out for pair correlations of the diffusion coefficients <i>D</i>_<i>i</i> and <i>D</i>_<i>j</i>. On the diagrams log <i>D</i>_<i>i</i> versus α^{<i>D</i>_<i>ij</i>} = <i>D</i>_<i>i</i>/<i>D</i>_<i>j</i>, the medians show the same trend as in the diagrams for permeability coefficients. The effects of temperature on the orientation of the clouds of the data points and upper bounds (limiting lines) of the diagrams log <i>P</i>_<i>i</i> versus α_<i>ij</i> = <i>P</i>_<i>i</i>/<i>P</i>_<i>j</i> were investigated using the available values of the activation energy of permeation. It was shown that for all the gas pairs the medians tend to shift down along the selectivity axis when temperature increases. Depending on a selected gas pair the slopes of the medians and upper bounds get either steeper or weaker. It was discussed that the positions and the slopes of the medians and limiting lines are sensitive to the Arrhenius parameters of gas permeation and temperature

Penetration of an external magnetic field into a multistrip superconductor/soft-magnet heterostructure

The magnetization of a planar heterostructure of periodically alternating type-II superconductor and soft-magnet strips exposed to a transverse external magnetic field is studied. An integral equation governing the sheet current distribution in the Meissner state of the superconductor constituents is derived. The field of complete penetration of magnetic flux in the critical state of the superconductor constituents is calculated for different widths of the superconductor and the soft-magnet constituents and a range of values of the relative permeability of the soft-magnet constituents.Comment: 2 pages, 1 figure; accepted in Physica C for the special issue of Proceedings of the 8th Int. Conference on Materials and Mechanisms of Superconductivity and High Temperature Superconductors (M2S-HTSC), Dresden, Germany, July 9-14, 200

Dense Hyflon® AD membranes for gas separation: influence of the solvent and determination of local free volume

Dottorato di Ricerca in: Scienze e Tecnologie delle Mesofasi e dei Materiali Molecolari, a.a. 2007-2008Università della Calabri

Self-Consistent Phenomenological Theory of Charge Injection at the Conductor/Insulator Interface

Self-consistent mean-field model of charge injection based on the matching of electric displacement and electrochemical potential in the electrode and the insulator is extended so as to account for discreteness of charge carriers. The improved scheme includes both the Schottky barrier lowering due to the individual image charge and the barrier change due to the field penetration into the injecting electrode. Applications of the theory to the cases of high-permittivity dielectric capacitors and organic light-emitting diodes are exemplarily presented