skip to content

Axel is graduated from ESPCI Paris (France), during which he reconstructed an in-vitro mimetic of a blood vessel using microfluidics, then worked on industrial filtration membranes for Evonik at Marl (Germany) and optimized the efficiency of sunscreen formulations for L'Oréal Applied Research in Chevilly-Larue (France). He now carries on a PhD project shared between the Vignolini group and the Centre de Recherche sur les Macromolécules Végétales (CERMAV) in Grenoble. This work aims at making photonic biomimetic hydrophobic polymer composites encapsulating cellulose nanocrystals (CNCs).

 

Above a threshold concentration, aqueous CNC suspensions are able to self-assemble into complex helicoidal structures capable of interactions with light after drying, namely iridescence phenomenon. However, a photonic CNC dried film is typically made of 100% CNC content, closely-packed stiff rods that lead to an intrinsic mechanical brittleness. As soon as other non-volatile components are added to the film, the photonic properties are often lost because the pitch value becomes too big to interact with light. By using a surfactant, one can drive a similar self-assembly in other solvents, including hydrophobic apolar solvents and monomers. The use of a surfactant changes the colloidal interactions in suspension, allowing for a pitch value slightly above the visible range. While aqueous suspensions need to be dried in order to yield iridescence, organic suspensions display visible colour effects without the need of drying. The initial polydomain microstructure of the suspension can be finely tuned by electric and magnetic fields, allowing one to favor some helices orientations or ultimately reaching a monodomain organization. The control of helices orientations shapes a collective optical response of the whole suspension, therefore optimizing the iridescence phenomenon. Finally, the helicoidal assembly and its orientation can be further retained by polymerizing the surrounding medium, leading to a composite iridescent material mimicking the colour effects found in nature. This material made of helical CNCs embedded in a polymer matrix has the mechanical properties of a typical composite, but also retains the photonic properties of its helical CNC content.

Visitor