Observation of Nano‐Dewetting in Colloidal Crystal Drying

The drying of colloidal crystals is connected with a continuous shrinkage process. However, several minutes after starting the drying, the system seems to take a breath before it shrinks monotonously until its final state after about one day. This short period we call “v”‐event because of the shape of the curve characterizing the lattice constant: a decrease followed by a counter‐intuitive increase which ends after one hour. This event is found in time‐dependent optical spectra. It is assigned to the start of a nano‐dewetting process occurring at the colloidal particles.     

Opals: Status and Prospects

The beauty of opals results from a densely packed, highly ordered arrangement of silica spheres with a diameter of several hundred nanometers. Such ordered nanostructures are typical examples of materials called photonic crystals, which can be formed by known microstructuring methods and by self‐assembly. Opals represent a self‐assembly approach to these structured media; such an approach can lead to novel materials for photonics, photocatalysis, and other areas. Although self‐assembly leads to many types of defects, resulting in the surprising and very individual appearance of natural opals, it causes also difficulties in technological applications of opal systems.