Villads Egede Johansen from DTU Mechanical Engineering defends his PhD "Structural Colours and Application to Anodised Aluminium Surfaces" Friday 20th February. The defence takes place in Building 101, room S01, DTU. Dr. techn. professor Ole Sigmund and Associate Professor Niels Aage from DTU Mechanical Engineering, and Professor Olav Breinbjerg from DTU Electrical Engineering are supervisors.
This thesis investigates possible ways of creating aluminium with a milky white, metallic appearance for decorative purposes. Since white cannot be obtained through traditional absorption based dyeing of aluminium, optical mechanisms based on scattering by nanostructures are studied in order to solve the problem.
The problem is investigated by first reviewing existing work within colouration and visual appearance. This includes a study on how colours are perceived by humans and an investigation of the characteristics with which a surface appearance is properly described. Subsequently, nanostructures and surface profiles are investigated using optimisation and topology optimisation in order to understand the limitations and design freedom of colour engineering. This is then followed by a study of the effect of disorder on a nanoscale level in order to tailor surface reflections for a smooth, pleasing appearance. Afterwards, optical models for scattering of non-deterministic geometries suitable for anodised aluminium are considered.
The outcome of the investigations are several different proposals for obtaining a White appearance for aluminium. These are described in the thesis alongside a brief note on the experimental work performed to try out the proposals. Results from the most successful experiment in which a satisfactory white appearance is obtained is then presented.
The colours of the peacocks feathers originate from structures in the surface. Photo: Colourbox.