Journal of Rheology, Vol.61, No.2, 217-228, 2017
Preparation and yielding behavior of pendular network suspensions
Particles suspended in a less-wetting fluid can be aggregated by addition of a small quantity of an immiscible fluid that preferentially wets the particles. If the added wetting fluid is sufficiently dilute, the aggregates are composed of particles held together by pendular menisci of the wetting fluid. Such pendular aggregates can then percolate into a network which endows the suspension with a yield stress. We examine the yielding behavior of pendular networks at a particle volume fraction of 20%, with wetting fluid loadings ranging from 0: 08% to 6: 4%. Steady shear experiments give a dynamic yield stress that increases roughly linearly with wetting fluid loading within the pendular regime, and the shear stress vs shear rate behavior can be collapsed onto a mastercurve by simply normalizing the stress by the yield stress. Linear viscoelastic moduli are found to decrease if the suspensions are sheared at a high rate prior to the modulus measurement, but this decrease can be reversed by shearing at a low rate. Various measures of yielding-the limit of linear viscoelastic behavior, the crossover of the storage and loss moduli in large amplitude oscillatory shear experiments, and strain recoil after cessation of shear-all suggest that the networks yield at similar to 1% strain. This strain is much smaller than expected from the micromechanics of rupturing pendular menisci, and we suggest nonhomogeneous deformation of the networks as the reason for the discrepancy. (C) 2017 Author(s).