UNUSUAL TIME DEPENDENT RHEOLOGICAL BEHAVIOR OF A CONCENTRATED SUSPENSION

The time dependent rheological behavior of a concentrated CaCO3 particle suspension is studied. The particles are suspended in a mixture of three industrial products: two resins, composed of styrene monomer, a styrene-butadiene-styrene block copolymer, and an unsaturated polyester oligomer, and one surfactant, acting as a dispersing agent for the particles. For the measurements, a MCR 301 rheometer from Anton Paar is used in the rotational mode, with a Couette geometry. An unusual behavior is observed, in which the low shear-rate viscosity of the suspension depends in a non-monotonous way on the shear rate applied during a previous shear history. The viscosity of the suspension at low shear rate depends both on the value of the prior shear rate, and the time during which it is applied. We found that the phenomenon is more pronounced when the particles volume fraction is increased. We propose an interpretation of the observed phenomenon in which links of different strengths can be formed between the particles and only the weakest links are destroyed by moderate shear rates.