  Colloidal crystals exhibit structural color without any color pigment due to
the crystals' periodic nanostructure, which can interfere with visible light.
This crystal structure is iridescent as the resulting color changes with the
viewing or illumination angle, which limits its use for printing or displays.
To eliminate the iridescent property, it is important to make the packing of
the colloidal nanoparticles disordered. Here, we introduce a drop-casting
method where a droplet of a water- ethanol mixture containing monodisperse
polymer-coated silica nanoparticles creates a relatively uniform and
non-iridescent deposit after the droplet evaporates completely on a heated
substrate. The uniformity is caused by a thermal Marangoni flow and fast
evaporation effects due to the heated substrate, whereas non-iridescence is the
outcome of short-range-ordered packing of nanoparticles by depletion attraction
and friction effects produced by polymer brushes. We show that the colors of
the final deposits from individual droplets remain unchanged while the viewing
angle is varied under ambient light. We expect that the coating method is
compatible with ink-jet printing and the uniformly coated self-assembled
non-iridescent nanostructures have potential for color displays using
reflection mode and other optical devices.
