Sofia Magkiriadou and co-workers demonstrated a simple and costless technique to produce an angle-independent colour. Core-shell colloidal particles consisting of high refractive index core and a soft shell were assembled in a disordered network by centrifugation. Constructive interference between light scattered from the high refractive index core occurs due to short-range correlations in the system. Since the structure is isotropic, the interference condition does not vary with orientation, leading to a colour that is independent of the viewing angle. By varying the distance between the scattering centres, simply by changing the thickness of the soft shells, it is possible to change the resulting colour. A similar mechanism is responsible for the colour of bird feathers.
Such materials may find application in cosmetics or display technology. Structural colour is in fact advantageous with respect to pigments, since it does not fade . Moreover, the fact that the shells respond to changes in temperature and pH lead to the possibility of using such materials for sensing application where a variation of the surrounding environment results in a change of colour of the device.
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