Light scattering from dilute solutions of critically branched epoxy resins

Summary Critically branched polymers were prepared from the bifunctional 4,4-diglycidyl-2,2-diphenylpropane (diglycidyl ether of Bisphenol A) and tetrafunctional poly(oxypropylene)diamine (Jeffamine D-400) at different distances from the gel point. Solutions of these samples in dimethylformamide were studied by static and dynamic light scattering. The results are discussed in terms of the classical Flory-Stockmayer theory and the percolation theory of gelation. The experimental results were found to be in agreement with the classical theory. The distribution functions of relaxation times were experimentally determined by the analysis of time autocorrelation functions obtained by quasielastic light scattering measurements on critically branched polymer solutions.     

Einfluß der Temperaturführung bei Warmverdrehversuchen zur Beurteilung der Warmumformbarkeit von Stählen

Warmverdrehversuche bei Temperaturen zwischen 700 und 1300 °C an technisch reinem Eisen sowie den Stählen 51 CrV 4, X 12 CrNi 18, X 7 Cr 14, X 47 CrMo 15 2, X 38 CrMoV 51 und X 125 CrMoV 5 11 und acht Versuchsschmelzen mit 0,44 % C, rd. 1 % Si und abgestuften Gehalten von Chrom, Molybdän und Vanadin. Versuche nach Erwärmen von Raumtemperatur auf Versuchstemperatur und nach vorangehendem Überhitzen auf Temperaturen zwischen 1000 und 1300 °C. Einfluß von Gefügeänderungen und Ausscheidungsvorgängen. Zusammenhang zwischen der Anzahl der Umdrehungen bis zum Bruch und der Umformtemperatur bei gleichbleibendem Gefügezustand.     

EDTA ester of bead cellulose a fast-kinetics chelating sorbent

Summary Crosslinked EDTA ester of cellulose (with 1–1.3 mmole bonded EDTA/g) was synthesized by the treatment of bead cellulose with EDTA bis-anhydride. Compared with the iminodiacetic acid resin, the cellulose EDTA ester exhibits a higher stability of Cu(II) chelates at low pH and a very high sorption rate of Cu(II). The sorbent is stable in neutral and acid medium, but is hydrolyzed by alkalies.     

Erbium-doped optical fiber fluorescence temperature sensor with enhanced sensitivity,a high signal-to-noise ratio,and a power ratio in the 520-530- and 550-560-nm bands

We analyze and predict the performance of a fiber-optic temperature sensor from the measured fluorescence spectrum to optimize its design. We apply this analysis to an erbium-doped silica fiber by employing the power-ratio technique. We develop expressions for the signal-to-noise ratio in a band to optimize sensor performance in each spectral channel. We improve the signal-to-noise ratio by a factor of 5 for each channel, compared with earlier results. We evaluate the analytical expression for the sensor sensitivity and predict it to be approximately 0.02 degrees C(-1) for the temperature interval from room temperature to above 200 degrees C, increasing from 0.01 degrees C(-1) at the edges of the interval to 0.03 degrees C(-1) at the center, at 100-130 degrees C. The sensitivity again increases at temperatures higher than 300 degrees C, delineating its useful temperature intervals.     

Characterization of polystyrene and doped polymethylmethacrylate thin layers

About 1 μm thick films of polystyrene (PS) and polymethylmethacrylate (PMMA) were prepared from solutions using spin-coating method. The PMMA films were doped with diphenylsulfoxide (DS) up to 45 wt%. Glass transition temperature (T _g ) of doped PMMA films was determined by DSC technique and relative permittivity (ε) as a function of the sample temperature was determined from capacitance measurement. The dependence of polarization (P) on electric field (E) and the temperature was measured using a standard Sawyer-Tower circuit. Spectral dependence of film refractive index was measured using a refractometer. The glass transition temperature T _g of PMMA/DS composite was found to be decreasing function of the DS concentration. Relative permittivity ε of unpolar PS is lower than that of polar PMMA. The PS permittivity does not depend on the sample temperature. For PMMA the permittivity is increasing function of both, DS dopant concentration and sample temperature. The dependence of the polarization on the electric field on PS film does not exhibit a hysteresis and indicate no polarization contrary to PMMA. PMMA/DS composites exhibit easier and larger polaribility and a permanent dipole moment. Resulting polarization is an increasing function of DS concentration. Refractive index of both pristine PS and PMMA decreases with increasing wave length. The refractive index of PMMA/DS composites depends on the DS concentration.     

Dielectric properties of doped polystyrene and polymethylmethacrylate

About 1 μm thick films of polystyrene (PS) and polymethylmethacrylate (PMMA) doped with diphenylsulfoxide (DS) up to 40 wt.% were prepared from solutions using spin-coating method. Glass transition temperature (T _g) of doped polymer films was determined by DSC technique. The depth profile and surface concentration of DS dopant were measured by RBS and XPS methods, respectively. The temperature dependence of relative permittivity of the films was determined from capacitance measurement. The dependence of polarization (P) on electric field (E) was measured using a standard Sawyer–Tower circuit. The glass transition temperature T _g of both composites was found to be decreasing function of the DS concentration. The DS doping leads to an increase of relative permittivity of the PS and PMMA films. RBS and XPS measurements reveal an outward diffusion of DS dopant in PS/DS films at elevated temperature. No such effect was observed in PMMA/DS films. PMMA/DS layers were found to be more thermally stable comparing to PS/DS.     

Plastic-bonded electrodes for nickel—cadmium accumulators. V. Influence of the current collector and mechanical compression on the current carrying capability of the nickel oxide electrode

Plastic-bonded nickel oxide electrodes, prepared by rolling a mixture of active material, conductive component and poly(tetrafluoroethylene), were subjected to high rate discharge cycling at 100 mA/cm² and to an accelerated cycling regime at 20 mA/cm². The number of cycles, the position of the discharge curve on high rate discharge, and the electrode impedance were found to depend on the quality and size of the collector surface and on the compression acting upon the electrode group in the cell.