The use of colour is ubiquitous in our society; we use colour to decorate our body and the environment that surrounds us. This use of colour can be traced back to prehistory, where people decorated the walls of their caves by making paints out of materials found in the surrounding areas, such as minerals like limonite or ochre, but also from charcoal.
The colour of traditional pigments relies on the use of materials with different chemical compositions that absorb light in a specific frequency range. However, the same pigment applied on different substrates or materials will provide a completely different optical appearance, due to a different interaction of the light with the environment: for example, the same pigment uniformly distributed on a flat surface will appear paler than when it is applied on a rough surface.
Aizenberg’s group proposes in this Optics Express article a fully scalable methodology to fabricate a new class of pigments that allows the design, a priori, of the colour appearance independently from where these pigments will be applied. The basic principle behind this achievement consists in engineering the light interaction within the absorbers. In particular, they propose a one-pot templated co-assembly method for bottom-up synthesis of pigments; the constituents of the pigment, metallic nanoparticles and silica, are combined on a substrate in a single self-assembly fabrication step (all the ingredients go inside the same container: one-pot) guided by the surface structure of the substrate (the template); the self-assembly process results in a photonic crystal doped with the metallic nanoparticles. The pigments’ colour is generated by the resonant plasmonic absorption of the nanoparticles with an additional light interaction via the photonic crystal (inverse opal); By manipulating the characteristic properties of the photonic crystals (such as porosity and wettability) they achieve colour effects that are not possible with standard pigmentation such as metallic shade, extreme brightness and dynamic colour change.
At last, it is possible to see a truly scalable methodology that allows obtaining structural pigments to better colour our life!
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