Scaling behavior of the elastic properties of colloidal gels

The scaling behavior of the elastic properties of colloidal gels that are well above the gelation threshold is studied both theoretically and experimentally. A scaling theory was developed by considering the structure of the gel network as a collection of flocs, which are fractal objects closely packed throughout the sample. Two regimes are found based on the relative value of the elastic constant of the interfloc links to that of the flocs. In the strong-link (interfloc) regime, the elastic constant of the gels increases but the limit of linearity decreases with increasing particle concentration, whereas in the weak-link regime both the elastic constant and the limit of linearity increase with increasing particle concentration. Rheological studies on the elastic behavior of two types of boehmite alumina gels, Catapal and Dispal powders, were performed. Both types of gels in the concentration range studied showed the strong-link behavior and the results are in good agreement with the theoretical predictions. The value of the fractal dimension of the flocs D1.95, deduced from the rheological measurements, is in agreement with the value D2.04 deduced from the static light-scattering measurements on dilute suspensions. Therefore the scaling theory we developed also enables us to extract structural information from the rheological measurements.