PhD project on photonastic phenomenona using computational chemistry

Contexte :

Photonastic materials convert light energy into mechanical energy and are the subject of pre-determined and repeatable deformations in response to light stimuli. This phenomenon is usually associated with plants and flowers whose petals open in the daylight and close in the evening in response to a light stimulus. In this PhD project, we are interested in bio-inspired polymeric photoactuator devices which can have applications in microfluidics, biomedics, soft robotics and motors. The keystone of these systems is the insertion of photoactive molecules, such as photochromes, within polymer films. They can undergo reversible photochemical reactions between two isomers that present different physico-chemical properties and, most often, significant structural modifications that can stimulate a large macroscopic shape-change in disordered or amorphous materials. While the number of experimental studies dedicated to photonastic materials, and more specifically to light-responsive polymers, is exploding, only few theoretical studies are dedicated to their investigation. Yet, their macroscopic behavior is likely dictated by atomistic/molecular scale processes, making computational chemistry the appropriate tool for understanding the unequivocal correspondence between the state of the photochrome and the shape of the film.

Objectif de la thèse :

In this PhD project, the aim is to identify, with the help of computational chemistry, the key parameters at the molecular and supramolecular scales involved in the mechanical response of a photoresponsive polymeric thin film. The challenge is to rationalize the multiscale mechanisms underlying these phenomena, namely the ultrafast photochromic reactions at the molecular level, the momentum transfer to the surrounding matrix, and after a cascade of processes, the long-term polymer relaxation which yields the macroscopic experimental deformation. The coupling between the photochromic reaction and the consequent behavior of the polymer matrix up to ~ 10 ps will be handled by a postdoctoral fellow prior to the beginning of the PhD project, using quantum chemistry and classical molecular dynamics. The objectives of the PhD project thus include the use of the previously proposed methodology to study the influence on the photonastic phenomenon of the strength of the photochrom/polymer interaction, the photochrome/polymer ratio and the time delay between two neighboring photochemical reactions. A final objective of the PhD project is to model the mechanical response of the polymer matrix on a longer time scale, up to 1 μs, using coarse-grained methods.

Déroulement de la thèse :

This PhD project will be supervised jointly by Aurélie Perrier at ENSCP and Claire Lemarchand at CEA. The work of the PhD student will be done at ENSCP with weekly meetings with both supervisors.

DIRECTEUR DE THESE

Aurélie PERRIER
aurelie.perrier-pineau@univ-paris-diderot.fr

ECOLE DOCTORALE

ED 388
Chimie Physique et Chimie
Analytique de Paris Centre
4 place Jussieu
Campus Pierre et Marie Curie
Case courrier 63
Sorbonne Université
75005 Paris

ENCADRANT

Claire LEMARCHAND
claire.lemarchand@cea.fr

CENTRE

DAM – Île-de-France
Bruyères-le-Châtel – 91297 Arpajon
Tél. : 01-69-26-40-00