Controllable introduction of defects into colloidal photonic crystals by co-assembly of latex spheres with different diameters and refractive index

Abstract

The controllable introduction of defects in colloidal photonic crystals (CPCs) is of great importance for their application in micro-photonic devices, such as low-threshold lasers, on-chip optical circuitry, fiber optics and so on. In this reported study, two kinds of latex spheres with different refractive indexes and diameters were prepared. One was an interpenetrating polymer network (IPN) of latex spheres composed of Fe3O4/poly(N-isopropylacrylamide)-poly(Acrylic acid) (Fe3O4/IPN) whose diameters were either 244.0 nm or 275.4 nm, and the other was composed of PNIPAM@(Fe3O4/IPN) core/shell polymer with a particle diameter of 316.3 nm. Doping the monodispersed Fe3O4/IPN latex spheres with larger PNIPAM@(Fe3O4/IPN) latex spheres followed by co-assembly, induced structural disorder in the product which perturbed the matrix periodicity so that defects were controllably introduced into the resulting crystal structure. This process was confirmed by presence of a narrow dip in the stop band of the reflection spectra. In addition, the synthesized defected-CPCs can also be reproducibly and reversibly tuned in minutes using external stimuli as a result of the stimuli-responsive property of the PNIPAM. These controllable, artificial-defect CPCs will enable modeling or control of the properties of light, and may find application in light switching, sensing, and optical computing.