Fine, equiaxed copper particles have been obtained by reduction of CuO in ethylene glycol. Cu, O always exists as an intermediate solid phase. Copper particles with a narrow size distribution within the micrometre range can be obtained if the nucleation and growth steps are completely separated and if agglomeration is avoided.Addition of D-sorbitol, which acts as a protective agent, prevents particle sintering. Addition of a strong base, e.g. NaOH, enhances the solubility of the precursor CuO and of the intermediate Cu,O. Under these conditions the overall reaction appears to be controlled by the nucleation and growth steps of the metallic particles. Their mean size can be largely controlled by varying the NaOH concentration. The synthesis of copper particles in liquid polyols, which act as both solvent and reducing agent, is a simple method for producing highly pure, equiaxed, non-agglomerated monodisperse particles.
On a etudie la variation de la température de transition vitreuse TV des copolymères du chlorure de vinylidène (CVD) avec l'acrylonitrile, le chlorure de vinyle et le méthacrylate de méthyle, en fonction de la composition de ces copolymères. A l'aide d'un modèle simulant, par la méthode de Monte‐Carlo, la croissance des chaînes et la cristallisation, on calcule la composition de la phase amorphe dans laquelle ont été rejetés, lors de la cristallisation, un maximum de c«défauts» comonomères. On explique ainsi, pour les copolymerès semi‐cristallins riches en CVD, l'écart entre la courbe experimentale et les courbes obtenues á partir des équations de Barton et de Johnston qui tiennent compte de la microstructure linéaires.
SynopsisThis is the first report on the characterization of several pairs of random copolymers of vinylidene chloride by gel-permeation chromatography in conjunction with viscometry. Such copolymers have not previously received much attention, so we first determined the individual viscosity-molecular weight relationship. The K-a values were compared with known values for the parent homopolymers. We then derived calibration cirves (different for each composition) and the calculation of the average molecular weight. These results are compared to those obtained by direct methods, without fractionation, and to kinetic observations. This method avoids misinterpretation of viscosity data and elution volume. Chromatograms may indicate heterogeneity of the compounds as related to polymerization conditions.
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