Photonic Paints: Structural Pigments Combined with Water‐Based Polymeric Film‐Formers for Structurally Colored Coatings

Abstract

Paints contain at least two components: a colorant and a polymeric binder, dispersed in a fluid medium. The first imparts color to the paint coating, while the second encapsulates the colorant upon drying in a robust polymeric film adherent to the surface substrate. Photonic pigments, inspired by nature's coloration strategy, hold promise as a replacement for toxic and fade‐prone absorptive colorants, most prominently in the fabrication of stable and sustainable water‐based paints. Crucially however, the step to combine photonic pigments with polymeric binders has not yet been taken. Here, a water‐based paint is designed and realized containing both photonic pigments synthesized by a scalable emulsion process and commercial polymeric binders in an aqueous dispersion. The photonic pigments are silica spheres containing a close‐packed array of air pores, of which both the periodicity and degree of long‐range ordering can be controlled to produce pigments of varying colors and degrees of iridescence. The readiness of the photonic paints for application is demonstrated by applying them like traditional paints in homages of famous artistic paintings. These findings should stimulate widespread application of structural pigments as colorants in not only paints but also a variety of industrially important materials, such as plastics, inks, or cosmetics.

Supraparticles for Sustainability

“…Although they offer a broad variety of colors, there are several drawbacks, such as photo‐ or chemical‐bleaching. [ 190,191 ] Additionally, in order to achieve different hues and optical effects, molecular dyes often have to be combined with supplementary compounds. A broad range of colors hence results in a multitude of chemical compounds, which increases costs of production and requires higher numbers of toxicity tests when brought into contact with the human body, for instance.…”

“…Comparing photonic pigments to conventional chemically colored pigments, photonic pigments exhibit some major advantages, especially in terms of (mechanical, chemical, thermal, …) stability and thus in terms of sustainability. [ 191,203 ] Since the coloring effects are generated from scattering events with nanostructured features and the nanoscale building blocks often consist of chemical‐ and photostable materials, photonic pigments usually offer nonfading properties. Therefore, they keep their intense color and brightness over time.…”

“…[ 196 ] On the contrary, chemicals of conventional colorants eventually degrade and this can cause environmental pollution and can add additional future work, as well as costs for repainting. [ 191,199 ] Therefore, the lifetime of products painted with photonic pigments as colorant can be increased dramatically. Furthermore, in contrast to conventionally used pigments, photonic pigments are not composed of any heavy metals or carcinogenic substances.…”

Mechanochromism in Structurally Colored Polymeric Materials

“…Photonic and plasmonic materials can now be used to control and manipulate the flow of light in a plethora of colorful applications in the modern world, ranging from microoptical components [ 10 ] and lasing materials [ 11,12 ] to household products, such as nontoxic and photostable pigments for paints and cosmetics. [ 13–15 ]…”

Brush‐Paintable, Temperature and Light Responsive Triple Shape‐Memory Photonic Coatings Based on Micrometer‐Sized Cholesteric Liquid Crystal Polymer Particles

“…Recently, structurally blue colored silica spheres have been reported as photonic pigments that can be mixed with a binder to form static photonic paints that can be brush‐painted. [ 24 ] Nevertheless, it still remains a challenge to fabricate stimuli‐responsive photonic multicolor paints exhibiting optical and topographical changes.…”