PolHydRaft

The main aim of our project is to develop an innovative RAFT-mediated emulsion polymerization process enabling to grow a thin polymer shell adopting the contours of Layered Double Hydroxides (LDH) nanoplatelets. The unique morphology of the resulting plate-like core-shell polymer-LDH-particles should result upon water evaporation into nanostructured composite films with LDH platelets oriented parallel to the plane of film formation. Such a microstructure should not only provide the film with enhanced mechanical properties, but should also strongly improve the barrier properties to water or gases by creating a tortuosity of the diffusion path way. To achieve the goal of this ambitious project, this project will be divided in two main parts: - The first part of our project will be devoted to the preparation of stable colloidal suspensions of macroRAFT-LDH hybrid particles. The synthesis of the two precursors: 1- LDH platelets with a large range of aspect ratios and charge densities prepared by soft chemistry, and 2- RAFT and macroRAFT agents carrying suitable carboxylic or phosphonic acid groups to permit their incorporation within the inorganic layers by electrostatic interactions, will be carried out in a first task. The second task will consist in assembling the above-mentioned partners to form the expected macroRAFT-LDH hybrid particles. Three different processes will be tested to prepare the hybrid materials: i) the macroRAFT agents intercalation by direct anion exchange on LDH platelets, ii) the direct coprecipitation of LDH in presence of macroRAFT agents and iii) the direct coprecipitation of LDH in presence of RAFT agent followed by in situ polymerization. According to the LDH charge density and the process used, various amounts of macroRAFT agents will be immobilized, influencing likewise the colloidal stability of the resulting macroRAFT-LDH hybrid particle suspensions. - The second part of the project will focus on the elaboration of LDH-based nanocomposite latex particles and the corresponding nanostructured films. The encapsulation of the LDH platelets will be carried out by RAFT-mediated emulsion polymerization. Careful selection of the experimental conditions and notably the nature and concentration of initiator, monomers and stabilizer will be realized to form a thin and uniform film-forming polymer shell of controlled thickness and composition following the contours of the particle shape. Particular care will be taken in the choice of compositions and concentrations of the different macroRAFT agents to avoid the formation of pure polymer particles by secondary nucleation and ensure a successful encapsulation. Finally, the microstructure and properties of the nanostructured films issued from the nanocomposite latexes will be characterized. In particular, the influence of the filler aspect ratio will be studied as well as that of the filler orientation. Taking into account such structural parameters, the mechanical behavior will be compared to classical modeling approaches in order to clearly establish the microstructure-mechanical properties relationships. This will allow optimizing the synthesis of the LDH-polymer core-shell particles owing to a quick feedback on the properties of the resulting films. The multidisciplinary nature of the project requires a combination of specific know-how. Accordingly, a team of young researchers from C2P2 and MATEIS (M. Lansalot and L. Chazeau, respectively) will be formed around Vanessa Prévot (LMI-Aubière), coordinator of this project to combine the necessary competences in the LDH chemistry and reactivity, in the RAFT and emulsion polymerization process and in characterization of nanocomposite properties.