Printing a Wide Gamut of Saturated Structural Colors Using Binary Mixtures, With Applications in Anticounterfeiting

Abstract

Use of colloidal suspensions to generate structural colors has the potential to reduce the use of toxic metals or organic pigments in inkjet printing, coatings, cosmetics, and other applications, and is a promising avenue to create large-scale nanostructures that produce long-lasting colors. However, expanded use of structural colors requires a reduction in coffee-ring effects during printing, which currently requires intricately patterned substrates or high particle concentrations, and diversification of colors to compete with conventional printing inks. Here, we treat substrate surfaces with cold plasma to facilitate spontaneous assembly of particles into colloidal nanostructures, reducing the need for highly concentrated particle suspensions. Moreover, by employing binary mixtures, we can tune the lightness of the hue produced or change the hue itself, allowing us to cover wider regions of color space. We demonstrate the use of this cold-plasma approach on a variety of substrates, favoring substrate diversity on which printing can be performed. This methodology enables creation of high-resolution, complex designs and opens a path for extending the limits of anticounterfeiting applications by using binary mixtures.

Structural Color Production in Melanin‐Based Disordered Colloidal Nanoparticle Assemblies in Spherical Confinement

“…[ 57 ] Researchers have used this strategy of mixing absorbing and nonabsorbing components to tune structural colors in the past. [ 39,58 ] However, whether the extent of mixing between the absorbing and nonabsorbing species affects structural coloration, as has been observed in case of some avian species, has not been systematically studied yet.…”

Characterization of broadband complex refractive index of synthetic melanin coatings and their changes after ultraviolet irradiation

“…18 In particular, two unique optical properties of melanin have been of interest for decades. One is the high refractive index (RI, $1.7-1.8), which results in vibrant structural colors 11,[19][20][21][22][23][24][25][26][27] and applications for medical diagnostics. [28][29][30] The second is the broadband absorption, which is responsible for enhancing saturation in structural colors, 11,[19][20][21][22][23][24][25][26][27] protection against UV radiation, 31,32 thermoregulation and imaging, [33][34][35] and optical contrast in photoacoustic imaging.…”

“…One is the high refractive index (RI, $1.7-1.8), which results in vibrant structural colors 11,[19][20][21][22][23][24][25][26][27] and applications for medical diagnostics. [28][29][30] The second is the broadband absorption, which is responsible for enhancing saturation in structural colors, 11,[19][20][21][22][23][24][25][26][27] protection against UV radiation, 31,32 thermoregulation and imaging, [33][34][35] and optical contrast in photoacoustic imaging. 36 Both of the above properties are expected to be influenced by UV radiation, especially considering melanin's tendency to undergo structural changes when it acts as a UV-protective agent with UV-dissipative and radical-scavenging abilities.…”

Progress in polydopamine-based melanin mimetic materials for structural color generation

“…of SiO 2 and PDA particles on an epoxy resin film containing thermochromic microcapsules that change from white to black with temperature ( Figure 9c) [116]. Additionally, it was shown that colloidal assemblies were efficiently constructed with a small amount of colloidal dispersion by using a substrate whose surface was perfluorinated by the cold plasma method.…”