Permeability relationships of polyimide copolymers

The permeability of the homopolymers 6FDA-3BDAF and 6FDA-4BDAF and of the copolymers 6FDA-4/2BDAF, 6FDA-4/3BDAF, and 6FDA-4/3/2BDAF to He, CO₂, and CH₄ was measured at 35.0°C and at pressures up to 10 atm. The experimental values of the permeability coefficients for the copolymers are in satisfactory agreement with the values estimated from the permeability coefficients for the constituent homopolymers and their weight fractions. The synthesis of the fluorine-containing diamine 2BDAF is reported for the first time. © 1994 John Wiley & Sons, Inc.     

Flourescence detection of surface exafs

The possibilities for flourescence detection of surface EXAFS are studied using thin films of gold on various substrates. For glancing incidence angles it is found that excellent signal to noise ratios can be obtained even for submonolayer films, demonstrating that the technique should have wide applicability to surface and near surface systems. In many cases the signal to noise is superior to electron detection techniques, and its sensitivity suggests the method may also be useful for detection of trace elements on surfaces.     

Harmonic confinement: A fully relativistic approximation to the meson spectrum

We propose a pair of covariant wave equations describing mesons as confined q$\text{q}$ pairs and realizing a spontaneously broken chiral symmetry. The system is Hamiltonian and does not contain unphysical solutions. The force is harmonic. The hyperfine splitting is given by the universal slope of the linear Regge trajectories.     

Solubility of carbon dioxide,methane, and propane in silicone polymers. Effect of polymer backbone chains

The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH₃)₂SiCH₂]_x and poly(tetramethyl silhexylene siloxane) [(CH₃)₂Si (CH₂)₆Si (CH₃)₂O]_x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared with similar measurements made with other silicone polymers. At a given temperature and pressure, the solubility of the above three gases is highest in poly(dimethyl siloxane) (Me₂SiO)_x. The gas solubility is decreased by either backbone-chain or side-chain substitutions of functional groups in (Me₂SiO)_x which increase the stiffness of the polymer chains and decrease the specific or fractional free volume of the polymers. It is conjectured that a decrease in the free volume of silicone polymers has a greater effect in decreasing the gas solubility than differences in gas/polymer interactions [with the exception of specific interactions (e.g., between CO₂ and polar groups in the polymer)]. © 1993 John Wiley & Sons, Inc.     

Mössbauer spectroscopic determination of surface magnetic anisotropy

This work was supported by NSF Grant No. DMR-8500889     

Increased Power Concentration and its Effect on the Discharge Parameters of the Low Pressure Hg-rare Gas Positive Column I. Variation of Current

By measuring the radiant flux of the resonance lines of mercury, the field strength and the electron energy distribution function the influence of the current on the parameters, especially on the energy balance of the Hg—Ar positive column is investigated, compared with a kinetic model, and interpreted. The decrease in yield of the 254 nm radiation with increasing current is linked to a corresponding increase of the losses due to elastic collisions with the rare gas atoms and is caused by the changes in the electron energy distribution function. Moreover, the influence of gas temperature, Hg-densities and effective life times is investigated.     

Diffusion of small molecules in polymers

A very large amount of information is available in the open literature on the diffusion, or transport, of small molecules in polymers. A comprehensive discussion of this field would require an amount of space exceeding by far the confines of the present monograph. It is to be hoped that this herculean but extremely useful task will be undertaken by some enterprising investigator, or investigators, in the not-too-distant future. In the meantime, a review is presented here of some of the important and more recent work on the diffusion of small molecules in both rubbery and glassy polymers. The main purpose of the review is to outline the thrust of this work and thus provide a perception of possible new developments in the field.     

Formation of ac Discharges Between Glass Insulated Electrodes in Ne + 1% N2 Mixtures. I. Experiments and Analysis

Ac plasma displays make use of medium pressure ac discharges in Penning mixtures between insulated electrodes. Discharges in Ne + 1% N₂ with glazed electrodes are a suitable experimental model showing the characteristic pulse and continous discharge modes. The axial optical space time structure of sinus wave sustained model discharges are measured with a scanning device, obtaining characteristic phases of discharge formation. Application of luminous flux method for stationary and dynamic Townsend discharges yields the first Townsend ionization coefficient α, and the comparison of the optical structure of ac discharges with that of dc discharges allows to explain the axial structure and to estimate the space charge effects.