UPR 5301

Axel FOUQUES’ s thesis defense on December 16th, 2020

This thesis is entitled "Bioinspired photonic cellulose films" and is co-supervised by M. Laurent HEUX, CNRS Researcher Director at Cermav- UPR5301, and Mrs Silvia VIGNOLINI, Professor at Cambridge University (United Kingdom)

“Cellulose nanocrystals are bio-sourced rod-like nanoparticles showing a remarkable iridescent optical response owing to their ability to self-assemble into cholesteric liquid crystalline phases above a threshold concentration. In the literature, 100% cellulose films and composite materials capable of impressive colour responses have been prepared respectively from aqueous suspensions by controlled drying and/or using organic and inorganic precursors. In this PhD work, we prepare materials from polymerizable cholesteric suspensions with the aim of developing a photonic optical response for a range of composite materials. In that extent, cellulose nanocrystals are compatibilised with organic apolar solvents and monomers using the steric stabilisation of a surfactant. The modification of colloidal interactions in apolar suspensions reduces the cholesteric pitch compared to aqueous suspensions, leading to an optical response at high angles of incidence already in suspension. The optical response in suspension is tuned by controlling the orientation of cholesteric helices using electric and magnetic fields before being locked into polymer composites. The retention of the cholesteric assembly of fillers and their field-aligned orientation preserves an iridescent optical response in the composites that is characterised in detail by angular-resolved spectroscopy. “