Spatial Segregation of Microspheres by Rubbing-Induced Triboelectrification on Patterned Surfaces

Abstract

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.

Self-organization of agitated microspheres on various substrates

“…Summarizing, consistent with our previous studies, 36,72 the data displayed in both Fig. 12 and 13 jointly show that, as a result of the tribocharging mechanism, the silica or polystyrene particles, independent of their size, and the CF x -coated substrates acquire opposite charges, positive and negative, respectively, after agitating the system.…”

“…However, as reported in previous studies, 36,72 no significant change in surface potential was measured on the surface of the particles or substrate in the case of the bare silicon substrates (not shown). A moderating remark in this respect is that, also in this case, it proved to be challenging to measure the charge on the particles after agitating them on the bare silicon substrate.…”

“…, these particles were less strongly adhered to the CF x -coated substrates before agitation. 36 This explains why only a small portion of the surface was scanned prior to agitation in Fig. 10a-1, a-2 and 10b-1, b-2 .…”

Microsphere Handling at the Microscale: New Tools and New Effects

“…Following the rationale to reduce particle adhesion, the silica particles would preferentially stick onto the silicon surfaces, whereas in the present study consistently the opposite is observed. We believe the clue to this observation can be found in our recent study, [97] where we have shown that rubbing-induced tribocharging leads to a preferential adherence of silica particles to CF x -coated surfaces (cf. Chapter 6).…”

“…Electrode in a Strong Electric Field of the CF x -coated wafers is described in our recent work [97] . The native oxide layer, typically of ca.…”