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We study both the activation energy for diffusion and dynamics of nanoscale clusters of a Frenkel-Kontrova chain subject to the microscopic friction, in connection with atomic friction phenomena. We clarify the atomistic mechanism for the presence of a magic size for diffusion and show how the magic size effects appear in the friction. When a cluster is pulled by a constant driving force, the critical force strength of depinning depends crucially on the cluster size, and it is smallest at the magic size. When a cluster is pulled by a spring at a constant velocity below the critical value, clusters show a stick-and-slip motion, and the maximum force of a spring also becomes smallest at the magic size.

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Evaluation of powder wettability is important to prepare well dispersed slurries. Therefore, in this study, a technique for evaluating powder wettability was developed to analyze the increase in the internal pressure of a closed powder bed due to capillary suction to determine the contact angle of the powder. The effect of the powder-bed-preparation method and powder surface area estimation method on the determined value of the contact angle was discussed. We demonstrated that the improved air permeation test proposed in this research can accurately determine the powder surface area, resulting in a faithful determination of the contact angle of the powder. It was also shown that compression under the shearing method could result in a denser and more homogeneous powder bed when compared to the conventional tapping method, indicating high reproducibility for estimating the contact angle.

Evaluation of powder wettability is important to prepare well dispersed slurries. Therefore, in this study, a technique for evaluating powder wettability was developed to analyze the increase in the internal pressure of a closed powder bed due to capillary suction to determine the contact angle of the powder. The effect of the powder-bed-preparation method and powder surface area estimation method on the determined value of the contact angle was discussed. We demonstrated that the improved air permeation test proposed in this research can accurately determine the powder surface area, resulting in a faithful determination of the contact angle of the powder. It was also shown that compression under the shearing method could result in a denser and more homogeneous powder bed when compared to the conventional tapping method, indicating high reproducibility for estimating the contact angle.