1986 Volume 14 Issue 1 Pages 37-42
Nonlinear viscoelastic properties of a carbon black - linseed oil suspension were investigated. Dynamic shear viscosity η′and rigidity G′ were measured using a newly constructed computer controlled rheometer, in which the amplitude of applied oscillatory shear could be held constant throughout the measurement. Measurements were performed at various strain amplitudes from 0.3% to 250% in the frequency range of 10-3-10 sec-1.
The values of η′ decrease with increasing angular frequency w and the curve of log η′ vs. log ω shifts downward with increasing strain amplitude γ. The frequency dependence of G′ is very small, and G′ decreases markedly with increasing γ. G′ and η′ are both independent of γ in the small strain region. However, at strains larger than 1%, they decrease with increasing y and the strain dependence of G′ is more remarkable than that of η′. The non-linear viscoelastic properties of the suspension may be attributable to the characteristic strain dependence of a network structure formed from dispersed particles. Since the rigidity depends on the network density, the network structure itself may be reduced with increasing amplitude of oscillatory shear.
A quantity ωγ was introduced in order to describe the effect of deformation rate on viscoelastic properties. The frequency dependence of G′ is rather strong, if the value of ωγ is kept constant. With increasing ωγ, the plot of log G′ against log ω shifts to higher frequency and the frequency dependence of η′ becomes weak. If the formation of network structure could be considered to be one of the relaxation mechanisms, the relaxation modes with longer relaxation times would be gradually diminished as the deformation rate increases.