Studies on interfacial electrochemical phenomena in pigment-vehicle systems.

Sedimentation potentials under a centrifugal field are studied with the disperse system titanium dioxide, alkyd resin and xylene. The relationships between the sedimentation potential and the rotation speed, the distance apart of the electrodes in the cell and the total weight of particles in the disperse system are examined. From the theoretical evaluation of the initial sedimentation potential, the zeta potential of the pigment in the disperse system is calculated. The calculated value was almost coincident with that obtained by the electrophoretic method. As the sedimentation potential is proportional to the total weight of pigment in the space between the electrodes in the cell, the particle-size distribution of pigment can be obtained from the sedimentation potential-time curve. The particle-size distribution in the above-mentioned disperse system was examined with respect to the effect of rotation speed and the pigment content. The modal diameter for the particle-size distribution obtained by this method had almost the same value as that obtained by the electron microscope method. By use of this method for particle-size analysis, the particle-size distribution for particles of diameter < 1 mum can be obtained in a short time (ca, 10-30 min) and the zeta potential of the particles in the disperse system can be calculated.