Influence of microstructure on the rheological behavior of dense particle gels

Rheological measurements are performed on highly concentrated alumina gels. Byusing an in situ mechanism based on enzyme-catalyzed internal reactions, we are able toform gels of highly concentrated particles without disturbing the microstructures thatdevelop during the gelation process. These gels are produced by two different destabilizationmechanisms: Either the pH of the suspension is shifted toward the isoelectric point(!pH method) or the ionic strength of the suspension is increased at a constant pH (!Imethod). The two destabilization mechanisms lead to gels of significantly differentmicrostructures. We find notable differences in the rheological behavior of the twosystems, suggesting a bond-bending mechanism for stress transmission in the case of !pHgels and a bond-stretching mechanism in the case of !I gels. In addition, for both kindsof gels we compare the in situ properties to those obtained after altering the microstructureby shearing. Results suggest an increase in elastic and yield properties of concentratedparticle gels with decreasing homogeneity of their microstructures.