Flow properties and electrical conductivity of carbon black–linseed oil suspension

Abstract

The electrical conductivity and apparent viscosity for suspensions of carbon black in linseed oil were measured at various volume fractions of carbon black as a function of rate of shear using a Couette type viscometer. The structural density may be reduced with increasing rate of shear and consequently the electrical conductivity and apparent viscosity decrease with rate of shear. The value of conductivity is proportional to the fourth power of concentration above a critical concentration. The viscosity also increases exponentially with increasing concentration. However, obvious threshold values of the concentration and of the power law index cannot be obtained. These phenomena are discussed in the framework of percolation theory. At intermediate structural density the electrical conductivity changes as the square of the viscosity. However this relationship is reversed when the denser structural networks are formed in the whole system. Since an oxidized boundary layer is gradually formed on the surface of the particles in the suspension of carbon black, the apparent viscosity and the electrical conductivity decrease with elapsed time. After reducing rate of shear, the conductivity and the viscosity increase with time due to growing flocculated structure. The value of conductivity reaches a maximum and then decreases, whereas the value of viscosity keeps increasing. These phenomena are discussed from a viewpoint of the kinetic processes of the formation and breakdown of the structural networks.