The relationships between drag reduction performance and polymer parameters including chemical structure, molecular weight, hydrodynamic volume, associations, and solvent nature were examined using synthetic water-soluble copolymers. Copolymer models were tailored to be systematically responsive to changes in electrolyte addition and included polyelectrolytes, polyampholytes, hydrophobically modified polymers, and uncharged, hydrophilic polymers. Commercial poly(ethy1ene oxide) (PEO) and copolymers of acrylamide with the comonomers sodium 3-(acrylamido)-3-methylbutanoate (NaAMB), sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS), [2-(acrylamido)-2-methylpropyl]dimethylammonium chloride (AMPDAC), and diacetone acrylamide (DAAM) synthesized in our laboratories were tested for drag reduction effectiveness using a rotating disk and a tube flow apparatus. Hydrodynamic volume as determined by viscometry and light scattering was monitored in deionized water and 0.514 M NaCl for particular compositions and molecular weights. Drag reduction performance was greatly affected by the nature of polymer/polymer and polymer/solvent interactions, generally increasing with hydrodynamic volume. Enhanced drag reduction behavior observed for the associating DAAM copolymers is proposed to be due to changes in water structuring in turbulent flow.
IntroductionThe reduction of drag in turbulent flow produced by addition of small concentrations of high molecular weight polymers has been studied for over 40 years.' Studies of polymers of varying structures have shown that drag reduc-
Co(OH) Liesegang periodic precipitation systems exhibit oscillations in the number of bands due to band redissolution in high NHOH concentration. We revisit the problem previously considered (Nasreddine and Sultan, J. Phys. Chem. A 1999, 103, 2934-2940) by rigorously refining the experiments and the Chaos analysis. Chaos is established in this diffusion-precipitation-redissolution system, as is evident from the refined outputs of the Chaos analysis tools. A brief account of possible applications of Chaos in Liesegang systems is presented.
Die aus dem Pyryliumsalz (I) (eingesetzt als Perchlorat) und Alkyhnagnesium‐ Verbindungen primär entstehenden 2H‐Pyrane (II) isomerisieren sich in schwach saurer Lösung unter Bildung der Methylendihydropyrane (III) (Ausbeuten mit wachsender Kettenlänge und Verzweigung des Alkyls abnehmend).
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