Mechanical properties of dense suspensions: Variations with interaction potential

The influence of interparticle potential on the rheology of dense suspensions was studied experimentally. Monodisperse submicron silica particles in aqueous solutions were used as model suspensions. The interaction potential between the particles was manipulated from repulsive to attractive by adjusting the concentration of KCl and cetyllrimethylammonium bromide (CTAB) in the solutions. The normal and frictional forces between pairs of the silica particles were measured directly with an atomic force microscope (AFM). The rheology of suspensions of the particles was studied with a constant stress rheometer.Suspensions of particles with repulsive interactions had smooth steady shear behavior, except during shear thickening. The shear stress versus shear rate curves for the suspensions were reduced to a single master curve by dividing the shear stress by the shear modulus and the shear rate by the modulus upon the continuous phase. This scaling was found to be only weakly dependent on the particle size, volume fraction, particle surface potential electrostatic decay length, and state of aggregation of the suspensions. Shear thickening did not follow the scaling.The moduli and yield stresses were measured for suspensions of particles with attractive interactions. The moduli and yield stresses increased with time upon the cessation of shear. Measurements of the modulus and yield stress, taken after a one half hour delay period, increased with the adhesive force between the particles. In addition, because the frictional forces between the particles were proportional to the adhesive forces, it was not possible to determine the independent effect of adhesion or friction on the moduli and yield stresses.U of I OnlyETDs are only available to UIUC Users without author permissio