MIcrofluidic for Seeds of Anistropic Particles – MIGRANI

The general objective of the proposal is to reach a better understanding of the growth of anisotropy in nanoparticular systems. For a decade, a rapid and burgeoning development of new synthesis routes has been performed and many materials are now available in the form of anisotropic nanoparticles (NPs) that are very promising for many applications. However, in most of the available wet schemes of synthesis in solution, the global size control is more advanced and understood than the shape control and due to a general tendency to polymorphism and pollution, a shape selection after synthesis is often necessary. The generation of anisotropy is not well controlled and this deserves further fundamental studies. This is where this proposal stands.
One difficulty is the two stages strategy used to produce anisotropic NPs. A first rapid stage produces seeds that are slowly grown afterwards. From the experimental point of view, many authors report the difficulty to obtain reproducible seeds with the classical laboratory methods. The seeds being very small, they are difficult to characterize experimentally and theoretically. The two stages strategy also brings conceptual questioning about the source of the anisotropy. When is it decided? during the generation of seeds or during the growth process? It is quite evident that the seeds are certainly not as anisotropic as the final particles but do they hide a trend to anisotropy since the very beginning or is the phenomenon expressed only during the growth stage whatever the seeds were?
The MIGRANI project aims at understanding the general problem of shape control of nanoparticles in wet synthesis. This ambition requires to: (i) obtain original data focused on the occurrence of anisotropy (ii) a strong coupling between experiments and theoretical simulations. Our approach of a comprehensive understanding is in strong contrast with the more classic ones in the field that are focused on the protocols needed to produce new particles. Four different types of complementary competences will be used: chemical synthesis, microfluidic systems for seeds production, developments of instruments for characterization and theoretical /simulation analysis.
- Regarding materials, we will focus on gold and iron oxyhydroxide because of their wide potential applications in the form of nanorods. For gold, the final yield and selection in rods is not perfect and the syntheses are very sensitive to the chemicals conditions. The issues are even more important for iron since the size control is far less optimized from the experimental point of view and the obtained particles are less monodispersed.
- Microfluidic chips will be used to produce the seeds. That type of mixing will guarantee a better control of seed production and improve the quality of the growth step, especially in the case of iron where the source of the poor monodispersity is unknown.
- The seeds and their growth will be characterized at different times by coupled techniques able to assess their structures at different length scales (ultra-high resolution Transmission Electron Microscopy (HR-TEM), cryo-TEM, (small angle X-rays scattering) SAXS/ (wide angle X-rays scattering) WAXS, UV-visible techniques). One objective is to produce a unique corpus of data onto well controlled seeds and their growth in order to base the theoretical models.
- From the theoretical standpoint, the main addressed question will be the transition towards anisotropy. Several mechanisms will be examined such as the atom-by-atom growth for which the main question will be the thermodynamic or kinetic control, or the directed aggregation that rather involves spatial and orientational correlations.
To perform the different tasks an interdisciplinary consortium of four laboratories is proposed. It will benefit from the conjugate competences and efforts or both physicists (theoreticians and experimentalists) and chemists of nanoparticles.