A large portion of the goods transported on earth is transported as granulates and powders. For a good processability of the powders their flow behavior is a dominant parameter. The smaller the particles become, the more dominant is the influence of the inter-particle forces on this flow behavior. The macroscopic behavior of such particulate systems is a complex interplay between the internal properties of the particles, their surface properties and the structure the particles form.
By choosing the appropriate particle chemistry, the interaction between the particles can be tuned from attractive and strongly binding to almost purely repulsive. Using mechanical testing and 3D structural analysis of the sample, correlations between particles interaction and the flowability become visible.
In case the particles are in contact with more than one liquid, the wetting behavior (and thus the surface properties of the particles) plays the dominant role in the particle interaction. When the interfacial energies allow a finite contact angle of the liquid interface on the particles. The wetting dynamics governs the microscopic as well as the macroscopic dynamics of the system.
Selected reference:
Roth, M., C. Schilde, P. Lellig, A. Kwade and G. K. Auernhammer (2012). "Colloidal aggregates tested via nanoindentation and simultaneous 3D imaging." Eur. Phys. J. E 35: 124.
Wenzl, J., R. Seto, M. Roth, H.-J. Butt and G. Auernhammer (2013). "Measurement of rotation of individual spherical particles in cohesive granulates." Granul. Matt. 15: 391-400.
