Self-assembly of biobased and non-iridescent structural pigments

This doctoral thesis was prepared at the Université Grenoble Alpes under the direction of Professor Alain Dufresne and the co-supervision of Cécile Sillard, Engineer (Grenoble INP - Pagora, UGA / LGP2).

Marlène Saulais presented the results of her research entitled Design and production of biobased and non-iridescent structural pigments, by self-assembly.

Structural colours are an interesting alternative to chemical colours, potentially toxic or photosensitive, and widely used in industry nowadays. Based on light/matter interactions, structural colour can be produced from bio-based and bio-compatible materials. Photonic systems producing structural colours in Nature are widely studied, and have inspired the scientific community in their attempts to synthesise artificial structural colours. The particularity of natural structures is their design targeting mainly short wavelengths, i.e. blue to green colours. Red in Nature mainly remains a chemical colour. Indeed, red is physically harder to produce, but is a crucial hue in the colour panel for some industries, such as the cosmetic field in which red colours remain chemically-based.

This PhD project aims to produce a red structural pigment, non-iridescent to avoid the angular-dependency of scattered colour, with bio-based and bio-compatible materials (for external uses), and with appropriate synthesis conditions for potential-scale up. As the structural pigment will be produced through a self-assembly process, the first part deals with the synthesis of the nano-building blocks, and their characterisation to conclude about their optical properties. The second part presents the assembly of the building blocks with two different strategies. And finally, the third part tries to go further in the bio-based approach, with the synthesis of new potential building-blocks.

This project is at the interface between chemistry and optics, where the former is used as a tool, sometimes being a source of constraints, to produce objects suitable for the latter.