Structural color coating films composed of an amorphous array of colloidal particles via electrophoretic deposition

Abstract

It is desirable to fabricate colorful coatings that have nonfading properties and are environmentally friendly. In this study, a novel approach for creating structural color coatings from monodisperse silica particles is presented. The structural color coating films, formed from an array of silica particles with a small amount of black additive, are easily prepared by a simple electrophoretic deposition (EPD) technique. The arrangement of the particle array is controlled by varying the applied voltage and deposition time. The iridescence, that is, the angular dependence, of the structural color dramatically changes with the arrangement of the particle array. A variety of colored coatings can be produced by changing the size of the particles. Structural color coatings on materials with curved surfaces and complicated shapes are also achieved by the EPD method. Quick deposition of silica spheres into roughly packed coatings creates the conditions needed to scatter light in fade-resistant colours. Instead of toxic dye molecules that change over time, paint researchers are turning to ‘structural colours’ that arise when submicron particles constructively interfere with light. Surprisingly, assemblies of submicron-sized particles with only short-range order display more-uniform colours than perfectly packed arrangements. Kiyofumi Katagiri from Hiroshima University in Japan and colleagues have now found that electrophoretic deposition of silica spheres can produce a variety of randomized structures thanks to a high assembly rate. Mixing a pinch of carbon black into the assembly of silica spheres proved critical to reducing incoherently scattered light in the films, whose colours were controllable by changing particle size. A variety of complex surfaces – even stainless-steel forks – could be coated by this method. Structural color coatings are prepared using the electrophoretic deposition (EPD) of SiO2 and carbon black particles. The arrangement of the particle array is controlled by varying the deposition condition. The angular dependence of the structural color changes dramatically with the arrangement of the particle array. Variously colored coatings can be produced on materials with complicated shapes.