Vane rheometry of bentonite gels

Abstract We describe the use of a four-bladed vane to measure the yield stress τ 0 of a series of aqueous bentonite clay suspensions. An extension of the vane technique is given, showing how the shear modulus G and the yield strain γ y can also be obtained. These techniques are validated by comparing the results with those obtained from conventional concentric cylinder rheometry at low clay concentrations where wall-slip is absent. A study of the clay concentration dependence is made for volume fractions (φ) up to 0.1. The magnitudes of τ 0 , G and γ y are found to scale closely as a φ x over the volume fraction range 0.01–0.1, with x approximating to 3 for τ 0 , to 4 for G and to −1 for γ y . Whereas x is largely time-independent, a increases with time for both τ 0 and G as the dispersions spontaneously gel.