Colloidal Photonic Crystals toward Structural Color Palettes for Security Materials

Abstract

Self-assembly of monodisperse colloidal particles into regular lattices has provided relatively simple and economical methods to prepare photonic crystals. The photonic stop band of colloidal crystals appears as opalescent structural colors, which are potentially useful for display devices, colorimetric sensors, and optical filters. However, colloidal crystals have low durability, and an undesired scattering of light makes the structures white and translucent. Moreover, micropatterning of colloidal crystals usually requires complex molding procedures, thereby limiting their practical applications. To overcome such shortcomings, we develop a pragmatic and amenable method to prepare colloidal photonic crystals with high optical transparency and physical rigidity using photocurable colloidal suspensions. The colloidal particles dispersed in a photocurable medium crystallized during capillary force-induced infiltration into a slab, and subsequent photopolymerization of the medium permanently solidifies the structures. Furthermore, conventional photolithography enables micropatterning of the crystal structures. The low index contrast between particles and matrix results in high transparency of the resultant composite structures and narrow reflection peaks, thereby enabling structural color mixing through the overlapping of distinct layers of the colloidal crystals. Multiple narrow peaks in the spectrum provide high selectivity in optical identification, thereby being potentially useful for security materials.

A colloidoscope of colloid-based porous materials and their uses

“…In addition, the synergy of the slow photon effect and the hierarchically porous structure of the inverse opal itself results in even higher photocatalytic activity due to enhanced surface area. 363,409 Recently, enhanced photocatalytic activity for degradation of organic compounds has been demonstrated in highly ordered meso/macroporous silica inverse opals impregnated with TiO 2 nanoparticles. 367 Ordered macroporous structures for photo-induced solar fuel production, such as hydrogen from water splitting, have received much attention in recent years (Table 1).…”

“…spherical photonic micro-particles) can be beneficial for many catalytic applications and is largely unexplored. 363,401,413 The control over metal NP size, distribution, and stability using a simple synthetic approach represents an additional challenge. Non-uniform distribution of functional particles can result in the formation of hot spots and compromise the uniform distribution of temperature and concentration profiles in the reactor channel.…”

Self-assembly of silica colloidal crystal thin films with tuneable structural colours over a wide visible spectrum

“…structural colours that cover a wide range of the visible spectrum [16,24]. Natural opals have SNPs generally in the size range of 150-400 nm and produce a range of structural colours [25].…”

Photonic Patterns Printed in Chiral Nematic Mesoporous Resins

“…Traditional lithographic patterning is complex, time consuming, and costly for large-scale generation and hence prohibitive for many applications. Because of that, self-assembly of colloidal particles has been widely explored and used to prepare patterned photonic structures through magnetic alignment, [15] extrusion and compression molding, [16] capillary force-induced infiltration, [17] or triphase microfluidic-directed assembly [18] followed by fixation in a polymer host. Patterning by the self-assembly of colloidal particles is limited by characteristics of the template and a multi-step fabrication procedure.…”