Uniform coating of self-assembled non-iridescent colloidal nanostructures using Marangoni effects and polymers

TL;DR

This paper presents a novel drop-casting method utilizing Marangoni effects and polymers to produce uniform, non-iridescent colloidal nanostructures suitable for optical devices and displays.

Contribution

It introduces a new technique combining thermal Marangoni flow and polymer coatings to achieve disordered, non-iridescent colloidal coatings with potential for printing and display applications.

Findings

Uniform coatings achieved via Marangoni flow and evaporation effects

Non-iridescent colors remain stable under varying viewing angles

Method compatible with ink-jet printing for optical device fabrication

Abstract

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.