Since the emergence of the nanotechnologies era in the 80s, block copolymers are frequently used to design host patterns allowing to control the structure of inorganic nanoparticles assemblies. The pivotal idea of MANIOC is at the opposite, it consists of manipulating the microstructure of triblock copolymers by adsorbing selectively their extremities onto the surface of "stimulable" and "guidable" nanoparticles. The experimental process, enabling the production of out-of-equilibrium microstructures on-demand, can be summarized in the following three steps : 1. Homogenization of the polymer matrix through magnetic hyperthermia. This step consists of irradiating magnetic nanoparticles embedded into the block copolymer with a high frequency oscillatory magnetic feld (ca. 1 MHz). The heat dissipation induced by the magnetic hysteresis then allows to heat quickly the material above its order-disorder transition temperature to make it liquid-like. 2. Reorganization of the nanoparticles into dipolar chains oriented according tot he magnetic filed lines. This step, which relies on the migration of magnetic nanoparticles, starts as soon as the host polymer has reached its disordered state. 3. Selective reassociation of the block copolymers at the interface with the nanoparticles upon cooling. This last step allows to pilot the microstructure of the polymer hard domains, based on the nanoparticles organization. Magnetic field lines can be adapted from the inductor geometry. The resulting material is a highly anisotropic thermoplastic elastomer. The system we target is based on a P2VP-b-PnBuA-b-P2VP triblock copolymer, or its P4VP counterpart, loaded with colloids of magnetite (Fe3O4). While the P2VP (Tg=100°C) is well-known to interact favorably with the surface of polar inorganic particles through hydrogen bonds, the PnBuA (Tg=-55°C) barely interact with them, ensuring a pronounced phase separation at the interface with the particles. One of the most challenging aspects of MANIOC resides in the simultaneous detection of the three constituants of the material: (i) the soft organic phase that occupies the largest part of the volume, (ii) the hard organic phase located at the interface with the nanoparticles, and (iii) the magnetic nanoparticles. To do so, we propose an advanced structural characterization that combines state-of-the art microscopy techniques such as Peak-Force AFM, chemical staining and electronic tomography. Beyond structural aspects, we expect the magnetic manipulation to impact significantly the macroscopic properties of the nanocomposites. In particular, we propose a series of rheological tests, performed both under moderate and large amplitudes, to investigate the structure-properties relationships in-depth. For the first time to our knowledge, we will also run rheological tests under high frequency magnetic stimulus, requiring the design of ceramic-based accessories. Beyond the mechanical effect, the manipulation of the organic phase is expected to enhance ions and gas permeability properties, notably through the formation of interfacial "tunnels", accelerating the diffusion of small molecules in the material. This part of MANIOC will possibly be oriented towards applications, notably in the fields of (i) solid-state battery polyelectrolyes, and (ii) gaz filtration membranes.

SUN7 is a fundamental research project, dedicated to Material Science. It aims at developing advanced experimental methods and characterization tools to monitor in-situ the phenomena occurring during setting and hardening of calcium phosphate cements for bone repair. This liquid-tosolid transition is indeed the key-point for successful biomedical applications, since it governs all functional properties, including the ease of handling by surgeons and mechanical and biological properties of set cements. In this framework, we intend to precisely characterize the setting process at different scales and with complementary quantitative methods. This global approach will permit to assess the chemical evolution and its reaction rate, the structuring of the paste, as well as the progression of its rheological and mechanical properties. Another important aspect of SUN7 is the 3D monitoring of microstructural features of a setting paste, using electron and X-ray tomography. This characterization in 4D (3 spatial + 1 time-related dimensions) will bring an unprecedented understanding of crystal growth and entanglements and of the formation of porosities during the setting process. Then, all results will be correlated to draw a global multiphysics and multiscale picture of setting and hardening processes. To do so, the impact of the different experimental methodologies on the setting process will be assessed; complementary in-situ approaches will be developed and, when possible, coupled. Finally, SUN7 will permit a thorough understanding of the whole process and of its kinetics. All experimental methods will first be developed and validated using gypsum plaster as a model material. Thus, this project will not only bring a comprehensive knowledge on setting of cements for bone repair, but will also be useful for a wide range of applications, including plaster and cements used in civil engineering. More generally, SUN7 will shed light on all studies related to the structuring of a mineral paste. Such a liquid-to-solid transition occurs, for instance, during the fabrication of ceramics or is sought for 3D impression. The development of advanced characterization methods in complex and specific environment (humidity, temperature) is another expected outcome of the project. Finally, the knowledge gained thanks to SUN7 will then have a strong impact to improve the biomaterials, which are currently commercialized.

Refractory high entropy alloys are known to retain exceptional mechanical properties at high temperature, with possible applications of these materials in extreme condition environments. The development of quantitative models able to predict the mechanical properties of these alloys as function of their composition, temperature and strain-rate would allow to speed-up considerably their development. However, the models currently available do not account for the role of interstitial solutes and diffusive mechanisms operative at high temperature. In this project, I propose to overcome these limitations by developing a multi-scale approach taking into account these mechanisms. Atomistic simulations will allow to parameterize a continuous model of a dislocation interacting with interstitial solutes. Second, the coupling of this model with interstitial diffusion will allow to investigate their influence on the mechanical behavior of the alloy (dynamic strain aging).

This project aims at establishing post-processing methods for a better understanding of the mechanical and fracture behaviour of nacre-like ceramic composites. These methods will couple two full-field measurement approaches, namely Raman spectroscopy for local stress field measurement and digital image correlation (DIC) for local strain field measurement. This coupling will be set-up during in-situ mechanical tests. A link between the measured Cr3+ ion fluorescence peak shift maps and the different stress tensor components will be established based on the local fields measured by DIC. Asymmetric notched specimen will be tested under bending in order to obtain mix mode loading at the notch and control the contribution of each stress component. Several notch geometries will also be studied to obtain different stress gradients at the notch. Experiment-simulation dialogue will also be established in order to enrich the analysis of the local measured fields. Considering the anisotropy of the studied nacre-like ceramic composites will enable improving existing post-processing approaches of mechanical tests of these materials, hence resulting in a better understanding of their mechanical behaviour and open new outcomes such as the full experimental determination of generalized stress intensity factors or interface property determination.

A material with strong rigidity and huge ductility and impact energy resistance is some kind of “graal” in the material science. In this project we propose a path toward this objective by combing the ultra-high-molecular weight polyethylene (UHMWPE) outstanding properties of impact and wear resistance with the metal rigidity. Such composite approaches are often challenged by processing issues such as the process temperature. In ARMURES project we propose to overcome these difficulties by using rapid sintering approaches. The choice of UHMWPE is essentially driven by its exceptional resilience properties, but it exhibits a relatively low stiffness (less than 1 GPa) due to medium crystallinity which justifies a metallic reinforcement. The choice of a metal is driven by its strong rigidity but also by the fact that it enables plastic deformation. The goal of the project is to develop new composites made of a double polymer/metal network, co-continuous or not by flash sintering, in order to explore a very broad ductility/rigidity spectrum. Moreover, the development of UHMWPE flash sintering is also linked to fundamental scientific questions such as the very long chain diffusion mechanisms, particularly by “melting explosion”. The chosen strategy is to start from the two following extreme situations: - Metal micro or nano particles dispersed in UHMWPE powder. Metallic particles (ferromagnetic) will allow induction heating, and so UHMWPE sintering in very short times and will strengthen the material. The relation process/microstructure/ properties will be preliminary evaluated at room temperature and then above UHMWPE’s melting temperature. This analysis, coupled with molecular dynamics modeling, will enable to advance in the understanding of the melting explosion mechanisms which are the main supposed mechanisms for UHMWPE nascent powder sintering. - A preliminary fabrication of metallic architectured materials which will then be filled with UHMWPE powder. The metallic material will thus be the vector of the heating by Joules effect or induction of UHMWPE powder allowing the sintering. These composites will therefore be co-continuous with a relatively well-controlled microstructure. These composites will be widely analyzed in terms of structure properties relations. In addition, the possibility of merging the advantages of the two previous strategies will be evaluated by trying a simultaneous sintering of low melting point metals and UHMWPE. This attempt, if it works, will be the first sintering metal/polymer material achieved in one step. Finally, the best composites obtained will be evaluated especially in terms of hydrodynamic cavitation resistance in view of applications such as marine or pumps propeller blades.