Characterization of microgels by Brookfield viscometry with cylindrical, T-bar, and flags impeller spindles

Abstract

Neutralized 0.5% microgels of the crosslinked copolymer of methyl vinyl ether and maleic anhydride were characterized by the penetrating ball test and by Brookfield viscometry with the # 7 cylindrical, T-E, and flag-impeller spindles. Apparent wall slip between the microgel and the #7 cylindrical spindle is a surface phenomenon that is more pronounced for “hard” microgels than for “soft” microgels and depends strongly on the interaction between the surface of the spindle and the microgel. Apparent wall slip can be enhanced by coating the #7 spindle with hydrophobic polymers and polymers with carboxyl groups and suppressed by coating the spindle with vinylpyrrolidone-based polymers. Similar apparent wall slip was also noticed for the cross-linked polyacrylic acid microgel. Apparent wall slip was not noticed when the T-E spindle and the flag-impeller spindle were used in viscosity measurement. The viscosity of microgels measured with a #7 spindle coated with polyvinylpyrrolidone, a T-E spindle, and a flag-impeller spindle correlate well with each other, indicating that the apparent wall slip is suppressed equally well by these three spindles. A simple penetrating ball test was used to differentiate hard microgels from soft microgels. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 67–74, 1999