Bubble-particle attachment efficiencies have been determined by measuring the collection efficiencies of single bubbles, with diameters between 0.75 and 2.0 mm and methylated quartz particles, whose diameters ranged from 5 to 80 pm, as a function of particle-water advancing contact angle and ionic strength. By performing experiments under conditions where the bubble-particle aggregate was stable and using a model for collision efficiency, both attachment efficiency and induction time were calculated. Smaller bubbles have larger attachment efficiencies than do larger bubbles for all particle sizes over a wide range of contact angles and ionic strengths. Induction times generally decrease with increasing attachment efficiency, except for fine particles with diameters less than about 10 pm, where they increase. Induction-time trends may be qualitatively interpreted in terms of thin-film drainage time as well as the time of formation of a stable wetting perimeter. The elementary steps in the bubbleparticle attachment process are not properly described by existing models.
A range of physical and chemical properties of flame‐sprayed ethylenemethacrylic acid copolymer (EMAA) were assessed, following different processing conditions. Coatings were produced at a range of specific temperatures by varying the propane flow rate and gun traverse rate. The flame spraying process oxidizes the EMAA copolymer during processing, the extent of oxidation increasing with greater deposition temperatures. Coatings were scanned using dielectric relaxation spectroscopy at a frequency range from 102 to 106 Hz over a temperature interval of ‐20 to 85°C. The glass transition temperature (usually denoted as the β′ relaxation in this system), is attributed to the microBrownian motion of long chain segments in the amorphous phase and is found to decrease with increasing deposit temperature. The oxidation process appears to reduce the position of the β relaxation due to chain scission. The molecular weight for the EMAA powder was reduced from 22,693 g/mol to 9302 g/mol when deposited at 271°C as shown by gel permeation chromatography. Despite the decrease in chain length, the activation energies for β′ relaxation increased with increasing coating temperatures. This is attributed to the increased polarity of the oxidized coatings resulting in greater intermolecular association, which outweighs the decreased chain length.
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