New Article in Chem. Mater.

posted Jun 7, 2013, 7:27 PM by Shin-Hyun Kim
 Hye Soo Lee, Tae Soup Shim, Hyerim Hwang, Seung-Man Yang and Shin-Hyun Kim, "Colloidal Photonic Crystals toward Structural Color Palettes for Security Materials," Chemistry of Materials, Accepted for Publication (2013)

Self-assembly of monodisperse colloidal particles into regular lattices has provided relatively simple and economical methods to prepare photonic crystals. Photonic stop band of colloidal crystals appears as opalescent structural colors, which are potentially useful for display device, colorimetric sensors, and optical filters. However, colloidal crystals have low durability and 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 photo-polymerization of the medium permanently solidifies the structures. Furthermore, conventional photolithography enables micro-patterning 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 potentially useful for security materials.