Post-deposition opal evolution.

The formation of artificial opal films consists of wet opal deposition, drying, and possible transformations in the dry state. The processes after deposition, before the crystals lattice reaches its final equilibrium state, are studied herein. We follow the time evolution of the optical transmission spectra for polystyrene opals with different thicknesses. The evolution of the spectra shows pronounced changes in the Bragg peak position, width and height, as well as changes in the background and, in the beginning of the process, a band related to residual water in the sample. Therefore, a wet and a dry phase can be distinguished in the opal transformations. They are all connected to shrinkage and we associate one of them with a possible new sintering mechanism.