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

Colloidal crystal (CC) thin films that produce structural colours over a wide visible spectrum have been self-assembled from silica nanoparticles (SNPs) using a natural sedimentation method. A series of colloidal suspensions containing uniform SNPs (207-350. nm) were prepared using the Stöber method. The prepared silica suspensions were directly subjected to natural sedimentation at an elevated temperature. The SNPs were deposited under the force of gravity and self-assembled into an ordered array. The solid CC thin films produced structural colours over a wide visible spectrum from red to violet. Visual inspection and colorimetric measurements indicated that the structural colour of the CC thin film is tuneable by varying the SNPs diameters and the viewing angles. The closely packed face-centred cubic (fcc) structure of the CC thin film was confirmed using SEM imaging and was in agreement with the intense colour observed from the film surface.