Novel starch microgels were prepared by emulsion cross-linking and characterized with respect to shape, volume, and mass density. Starch microgels appear to be negatively charged (∼−50 mV), with a particle size varying as a function of the type of cross-linker (ca. 0.25-10 µm). Environmental scanning electron microscopy observations show a dependence of the particle swelling on the cross-linking density. Viscosimetry reveals that starch microgels behave as charged polymers, where the reduced viscosity increases with dilution (anomalous viscosity behavior) for sufficiently low κa (ca. κa < 3), the ratio of the particle radius (a), and the Debye length (κ −1 ). Analogous results are obtained for reference-charged rigid silica spheres, which approach the hard sphere limit for increasing ionic strengths. The shape of the microgels appears to play a minor role in the anomalous viscosity behavior, which is more likely dominated by electrostatic effects. C 2002 Elsevier Science

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