How particle properties affect the assembly and characteristics of colloidal particle bands

The interaction of suspended particles with a planar wall is a classic problem of colloid science. Particle-wall interactions in a flowing suspension are a newer area of interest, motivated by applications in microfluidics. Recent studies show that radius $a =$ 245 nm particles in a dilute (volume fraction $\varphi =$ 0.17\%) suspension are attracted to the wall, form 1D ``pearl chains,'' then assemble into concentrated streamwise bands with a roughly constant cross-stream spacing in combined Poiseuille and electroosmotic flow through fused-silica microchannels. The bands only exist within a few $\mu$m of the wall, and occur above a minimum shear rate $\dot{\gamma}$ and electric field magnitude $|E|$. Attracting (\emph{i.e.}, concentrating) the particles to (near) the wall is a prerequisite for band formation; however, bands are not observed in all cases when particles are attracted to the wall. Particle properties appear to have a significant effect on these phenomena: decreasing $\varphi$, for example, appears to increase both the minimum $\dot{\gamma}$ and $|E|$ for band formation. Results are presented on how the assembly and characteristics of the bands are affected by properties such as $\varphi$, $a$ (where $a < 1~\mu$m), and zeta-potential $\zeta_{\rm p}$.