| Adhesion between surfaces plays a critical role in the macroscopic behavior of particulate systems such as the flow of cohesive powders, the removal of particulates from substrates, and the formation of particulate coating on host surfaces. Similarly, the repulsive force profile between two particles in suspension influences properties such as rheological behavior and polishing efficiency. The majority of theoretical predictions of surface forces assume that the interface between the particle and surrounding media is ideal. Namely, that there is an atomically sharp demarcation between the properties of the bulk material and the properties of the medium. Furthermore, the interface is often considered perfectly monotonic. While this assumption is likely valid at larger separation distances, significant deviation from theory is expected when two particles are in a contact or near-contact configuration, as they are in adhesion processes or high force operations.; This study explores the impact of the non-ideality of surfaces on the adhesion between particulates in dry and humid atmospheres as well as in solution. Specifically, the influence of nanoscale roughness in the range of 0.2 to 20 nm RMS has been investigated on the van der Waals, polar, and capillary forces that bind particulates together or prevent particulate removal from surfaces. Additionally, the influence of transition layers, consisting of chemically modified layers of nanoscale thickness at the interface, on the interaction of particulates in suspension has been delineated. For each of these cases, theoretical predictions are developed and validated through direct measurement of surface forces. The presence of non-ideal interfaces is determined to have a significant impact on the magnitude of the surface force that govern the ensemble behavior of many particulate systems. |
