Rheology of agar microgel dispersion

Rheological behavior of agar microgel dispersion was studied. Agar microgel dispersion was prepared from agar bulk-gel containing 1.3-1.7% agar which was determined by a high-speed-mixer (5,000 rpm). To confirm the mechanical property of the microgel, we measured the dynamic modulus of the microgel dispersion. The microgel dispersion showed a gel-like nature in a small deformation range (gamma < 1%) while the dispersion showed a fluid-like nature in a large deformation range (gamma > 1%). The flow charactetistic parameters including yield stress and apparent viscosity of the dispersion were calculated by using Herschel-Bulkley equation of the scaling law model. The microgel showed pseudoplastic-flow with a yield stress (about 13 Pa). The apparent viscosity of the dispersion depended on the hardness of the individual microgel particles. To investigate the effect of the microgel volume fraction on its flow characteristic parameters. we examined the parameters of several microgel dispersions with various volume fractions ranging from Phi(gel) = 1.0 to 0.3. The yield stress of the microgel dispersion decreased suddenly at around Phi(gel) = 0.7 and disappeared at around Phi(gel) = 0.4. The apparent viscosity of the microgel dispersion also decreased with the decrease of Phi(gel). The result indicates that packed condition of the microgel particles mainly reflects the Theological properties of the microgel dispersion.