The nature of these heterogeneous regions has remained a puzzle. The figure shows a 13.3-second time exposure of a monolayer of 1.6 micron silica spheres suspended in water between two glass plates, viewed in an optical microscope. Video data was processed to show only the tracks of the centers of the spheres. Tracks that intersected within the exposure time are shown as heavier lines. Longer trains of tracks are shown in color.
Different colors distinguish nearby but distinct tracks.
This striking heterogeneity suggests ways of controlling the rheology and molecular diffusion of viscous industrial fluids as well as dense colloidal suspensions as used in paints.