CHAPTER 3: Opal Photonic Crystal Films with Tunable Structural Color
Published:15 May 2013
Close‐packed monodispersed colloidal spheres form three‐dimensional ordered structures that diffract selected visible wavelengths of light. This phenomenon, known as Bragg's diffraction, can be commonly observed as iridescence in opals, which results from their structure. High‐quality opal films of cubic close‐packed (ccp) colloidal crystal structures can be formed using a self‐assembly process. These opal films have colloidal sphere arrays with (111) oriented surfaces, and the space between the colloidal spheres is filled with elastic materials. In addition, the structural color of the opal composite films can be tuned using external stimuli. Swelling and mechanical strain changes the lattice distance of the ccp (111) planes in the opal composites. The change in structural color is caused by tuning of the stop bandgap in opal photonic crystals. Potential engineering applications for tunable structural color or shifting Bragg's diffraction wavelength materials include chemical sensing, color displays, textile fibers, and strain imaging.