カーボンブラック-アマニ油分散系における動的粘弾性の時間依存性

抄録

Time-dependent viscoelastic properties of a carbon black-linseed oil suspension were investigated using a computer-controlled double cone type rheometer in which the amplitude of applied oscillatory shear could be held constant. Dynamic shear viscosity η′ and rigidity G′ were measured at a frequency of 0.628 rad/sec at relatively small strain amplitudes, 0.5, 1 and 2%. The suspension of carbon black in linseed oil shows a remarkable thixotropic behavior, which is attributable to the change in density of interparticle network structure. The structure seems to change in deformation and to depend on strain amplitude, rate of strain, and strain history. During the structural recovery after cessation of steady shear flow, the values of G′ at strain amplitudes of 1 and 2% reach equilibrium values after attaining maxima. The stress level of the peak values of G′ is close to the yield stress of the system. This phenomenon may be attributable to competition between rupture by oscillation and formation of structural networks. The rupture of the networks increases the internal friction and leads to an increase of viscous component of the system. The kinetics of the formation and the rupture of the interparticle structure can be described by a kinetic equation using structural parameter Q presented by Chaffey. The viscoelastic properties during structure build-up leading to the dynamic equilibrium can be predicted using an empirical kinetic equation that takes into account the kinetic processes of structural networks and the increment of the viscous component due to rupture of the networks. The characteristics in time dependence of the viscoelastic properties at each strain amplitude mainly depend on the rate constant for breaking down of the growing network structure k_t; with increasing strain amplitude, the value of k_t, increases remarkably.