Scaling Behavior of the Rheological Properties of Montmorillonite Suspensions: Correlation between Interparticle Interaction and Degree of Flocculation.

In this work we investigate some aspects of the rheological behavior of sodium montmorillonite (NaMt) suspensions in the pH range 3 to 9, of NaCl concentrations between 10(-3) and 10(-1) M, and of solid concentrations between 5 and 11% w/v. Three kinds of experiments were performed: steady-state viscometry, oscillatory test, and creep recovery. The physical quantities of interest were the yield stress sigma(y) of the suspensions, the elastic rigidity modulus G', and the instantaneous elastic compliance. Furthermore, G' was obtained from oscillatory tests in three different experiments: determination of the viscoelastic linear region, oscillograms, and the gelation process. All quantities were found to scale with the concentration of solids, C, according to a power law of the form Y=k(y)C(n). The exponents n were found to change from approximately 3 to approximately 6 when the pH was increased from 3 to 9 (at constant ionic strength 10(-2) M), although values as high as 10 were estimated when the NaCl concentration was reduced to 1 mM. Such values of n correlate well with the characteristics of the edge-to-face (E-F), edge-to-edge (E-E), and face-to-face (F-F) interparticle interactions. The minimum values of n correspond to maximum E-F attractions, whereas the largest n are associated with strong F-F repulsions. Copyright 2001 Academic Press.