Optical properties of a Portable Colloidal Array

Colloidal crystals with hexagonal closed packed (HCP) ordering can be obtained on a planar surface by simple spin coating technique, in presence of trace amount of surfactant. By spin coating on a topographically patterned substrate we can also obtain ordered colloidal structures with non-HCP ordering. It is however not possible to obtain a non-HCP ordering on a flat substrate without any chemical or topographic patterning. We have developed a method by which we can overcome this problem, by fabricating the array on a patterned UVO degradable polymer layer and subsequently transfering the array on to another substrate. The flexible nature of the master makes it possible to transfer the array on to non-planar substrates. Our proposed method allows the colloidal structures to be transported across substrates irrespective of their surface energy, wettability or morphology. The transmittance data of the transferred non-HCP colloidal arrays on glass show wide-spectrum anti-reflectivity, yielding about 99.5% transmission over the entire spectral region between 450 and 1700 nm. Reflectance of glass is also reduced to 3.3% over the entire spectral region.