The vibration dynamics of relatively large granular grains is extensively treated in literature, but comparable studies on the self-assembly of smaller agitated beads are lacking. In this work, we investigate...

Particle (monolayer) assembly is essential to various scientific and industrial applications, such as the fabrication of photonic crystals, optical sensors, and surface coatings. Several methods, including rubbing, have been developed for this purpose. Here, we report on the serendipitous observation that microparticles preferentially partition onto the fluorocarbon-coated parts of patterned silicon and borosilicate glass wafers when rubbed with polydimethylsiloxane slabs. To explore the extent of this effect, we varied the geometry of the pattern, the substrate material, the ambient humidity and the material and size of the particles. Partitioning coefficients amounted up to a factor 12 on silicon wafers, and even ran in the 100's on borosilicate glass wafers at zero humidity. Using Kelvin Probe Force Microscopy, the observations can be explained by tribo-electrification, inducing a strong electrostatic attraction between the 1 particles and the fluorocarbon zones, while the interaction with the non-coated zones is insignificant or even weakly repulsive.

Triboelectrification is the spontaneous charging of two bodies when released from contact. Even though its manifestation is commonplace, in for instance triboelectric nanogenerators, scientists find the tribocharging mechanism a mystery. The primary aim of this mini-review is to provide an overview of different tribocharging concepts that have been applied to study and realize the formation of ordered stable structures using different objects on various length scales. Relevance spans from materials to planet formations. Especially, dry assembly methods of particles of different shapes based on tribocharging to obtain crystal structures or monolayers are considered. In addition, the current technology employed to examine tribocharging in (semi)dry environments is discussed as well as the relevant forces playing a role in the assembly process. In brief, this mini-review is expected to provide a better understanding of tribocharging in assembling objects on the nano-and micrometer scales.