Application of the Hydrodynamic-Structural Theory of Non-Newtonian Flow to Suspensions which Exhibit Moderate Shear Thickening with Particular Reference to “Dilatant” Vinyl Plastisols

Abstract A general equation, derived in previous work, fits flow data for moderately shear thickening dispersions of poly (vinyl chloride) particles in an oil. The theory on which the equation is based predicts that the number of structural links in a disperse system can increase with increasing shear rate without shear thickening, provided n∞/n0<2 , where n∞ and n0 are the number of links per cubic centimeter at infinite shear rate and zero shear rate, respectively. This could account for the unexplained occurrence of “volume dilatancy” without “rheological dilatancy” previously reported in the literature. When n∞/n0<2 , viscosity increases with increasing shear rate to a maximum value and then the viscosity decreases with further increase in shear rate. This effect is explained as a competition between increase in the number of links with increasing shear rate and decrease in link lifetime with increasing shear rate. Aging of vinyl plastisols is examined and found to involve changes in both hydrodynamic and structural viscosity which can be explained by absorption of oil into the porous poly (vinyl chloride) particles.