In nature some animals make use for structural colours, instead of pigment colours, to interact or camouflage with the environment around them. Structural colour comes from the interaction of light with the structures in a material and for this reason does not fade like normal pigments do. Inspired by nature, these colours can be mimicked by arranging monodisperse colloids in crystals by making use of self-assembly. When the size of the colloids are on the order of visible light (400-700 nm) structural colours can be seen.

Colloidal crystals can be used as templates to create inverse opal structures. The amount of order and disorder in the crystalline structure allows structural colours to have different properties. In highly ordered photonic crystals the structural colour shows an angular dependence, when a low degree of disorder is introduced the structural colours begin to have a much lower angle dependence. However, once the disorder in the crystal becomes too large, the structural colour is lost and the surface appears to be white, as the light is scattered in all directions.

This project is looking at introducing disorder into self-assembled colloidal crystals by making use of non-spherical dimpled particles as templates. The particles with dimples introduce a different type of disorder into the system, with the idea that the order of the disorder can be controlled by the size of the dimple in the particle itself. Different self-assembly approaches are looked at, thin film evaporation deposition, gravitational sedimentation as well as confined self-assembly within a water-in-oil emulsion. The methods needed to create inverse opals as well as the viability of inverting these different self-assembled structures are also looked into. The final particle arrangements within the self-assembled structures and the visible light reflection spectra (in real and in reciprocal space) will be used to compare the methods.

The synthesis of the dimpled particles results in drastic changes of the surface properties of the particles, changing from hydrophobic polymeric particles to hydrophilic carbon based particles. These changes impact the self-assembly behaviour in the system, as the hydrophobicity of the particles play a role in the way particles self-assemble in evaporation deposition. This required modifications to the particle synthesis and a particle surface preparation with the assistance of surfactants, to enable the particles to be stable enough to form ordered crystalline arrangements.

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Liu, P., Bai, L., Yang, J., Gu, H., Zhong, Q., Xie, Z. and Gu, Z., 2019. Self-assembled colloidal arrays for structural color. Nanoscale Advances, 1(5), pp.1672-1685.