Evaluation of the particle-particle interactions in a toner by colloid probe AFM

In order to evaluate the particle-particle interactions in a toner particle with a high accuracy, the changes in the adhesion force between a toner particle glued to an AFM cantilever tip and a particle in a compressed layer of toner powder was measured by colloid probe atomic force microscopy. Toner particle layers compressed by a pressure of 54.9 MPa were used as the substrate in this study. The effects of the scan rate, particle diameter, humidity, and surface coating of silica nanoparticles on the adhesion force were discussed on the base of measurement results. The adhesion force between the toner surfaces decreased with an increase in the AFM scan rate; it then reduced to a constant value at 1.95 Hz. The adhesion force between the toner particles increased proportionally with approximately the second power law of the particle diameter; it exhibited a change that differs from the force characteristic that was directly proportional to the first power law of the particle diameter, as given in van der Waals expression. Next, the additives that consisted of SiO2 were glued on to the surface of the toner particle, and the influence of the surface coverage Of SiO2 on the particle-particle interactions was examined. The particle-particle interactions consequently decreased in inverse proportion with a surface coverage of SiO2 26% or less. Moreover, when the SiO2 surface coverage was 26%, almost no changes were observed in the particle-particle interactions at 80% R.H. It was confirmed that the influence of humidity reduced by coating the toner particle with SiO2. The relationships between the particle-particle interactions and the flow properties were examined by using a rotary shear tester with a conical rotor. When the mean particle diameters were identical, a first strong positive correlation between the particle-particle interaction and the shearing torque that crossed the zero point was observed. When the shearing force H was calculated from the torque of the conical rotor method by using Rurnpf's equation, a first strong positive correlation between the particle-particle interaction Fa and the shearing force H that crossed the zero point was observed. (c) 2007 Elsevier B.V. All rights reserved.