THE EXISTENCE OF STATIC YIELD STRESSES IN SUSPENSIONS CONTAINING NONCOLLOIDAL PARTICLES

Many previous investigations have established and/or quantified yield stresses in suspensions of interacting (colloidal or surface active) particles. In this work it is shown for the first time that highly filled suspensions of noncolloidal particles can also exhibit a static yield stress sigma(s). The determination of static yield stresses in these systems was made possible by conducting very long time (up to 6000 h) tensile creep tests. These tests are particularly suitable for high viscosity systems such as the suspensions examined here and also have the advantage that there is minimal influence on the results due to the measurement apparatus. Through these experiments, it is possible to observe an unambigious change of material response above and below the static yield stress sigma(s), with viscoelastic solid-like behavior exhibited below sigma(s), and viscoelastic liquid-like behavior above sigma(s). The dependence of this static yield stress on the volume concentration filler is examined in this work.