Rheological Properties of Rodlike Particles in a Newtonian and a Non‐Newtonian Fluid

The macroscopic rheological behavior of suspensions of nearly monodisperse glass fibers having a mean aspect ratio, ār, of 24.3 and a mean length, L, of 267 μm, and commercial ground glass fibers, ār=7.6 and L=84 μm, were studied. Volume fractions of 0.02, 0.05, and 0.08 were used. For Newtonian suspending fluids, the shear viscosities and the dynamic linear viscoelastic properties of the suspension showed Newtonian behavior. In a stress growth experiment, the shear stress obtained a maximum value before reaching steady state. Upon reversal of shearing, a similar stress growth pattern was retraced. The non‐Newtonian suspending fluid, a polyisobutylene in cetane solution, was found to behave as a second‐order fluid at low shear‐rates and frequencies and shear‐thinned at higher values. Suspensions in this fluid also behaved as second‐order fluids at low shear‐rates and frequencies. The dependency of two of the second‐order fluid constants upon the volume fraction of particles was determined.