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Nucleation from atomistic to colloidal approaches - Julien Lam - Vendredi 22 janvier 2016 à 10h

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-12 - 4e étage, salle 426

Julien Lam - HH Wills Physics Laboratory - University of Bristol

Abstract

Nucleation mechanisms cover many applications, in material science including soft matter, pho- tonics and biotechnology. Yet, the transient nature of the nucleation core limits most of the ex- perimental investigations and a predictive modeling of nucleation is still not achieved. Since the beginning of the 19th century, classical nucleation theory (CNT) has been used for intuitive descrip- tions. CNT appears to be successful for liquid nucleation in a supersaturated vapor. However, this approach remains controversial regarding quantitative results and also presents conceptual limita- tions. In this presentation, I will introduce two alternative approaches to nucleation. First, we investigated the formation of the nucleation core using -rst-principle calculations. Ge- ometrical structures and thermodynamic properties of aluminum oxide clusters AlxOy are obtained and employed to study the chemical composition of a gas made of aluminum and oxygen atoms as a function of the temperature, the pressure and the aluminium to oxygen ratio. This modeling is con- fronted to experimental results obtained via laser ablation of a solid target. At high temperature, a remarkable agreement is found allowing us to extend the calculation to lower temperature where we monitored the formation of alumina Al2O3 -rst seeds. (Al2O3)3 and (Al2O3)4 are thus expected to serve as nucleation core for alumina growth. In the second part of this presentation, I will describe how colloidal mixtures may enable to unveil the nucleation processes. Especially, I will present how hard-spheres behave under spherical con-nement and try to elucidate the crystallization processes under these particular conditions. References [1] J. Lam, V. Motto-Ros, D. Misiak, C. Dujardin, G. Ledoux, D. Amans, "Investigation of Local Thermodynamic Equilibrium in Laser-induced Plasmas : Measurements of Rotational and Excitation Temperatures at Long Time Scales", Spectrochim. Acta B, 101, 86-92 (2014). [2] J. Lam , D. Amans, C. Dujardin, G. Ledoux and A-R. Allouche, "Atomistic Mechanisms for the Nucleation of Aluminium Oxide Nanoparticles" J. Phys. Chem. A, 119, , 8944-8949 (2015). [3] B. Nijs, S. Dussi, F. Smallenburg, J. D. Meeldijk, D. J. Groenendijk, L.a Filion, A. Imhof, A. van Blaaderen and M. Dijkstra, "Entropy-driven formation of large icosahedral colloidal clusters by spherical con-nement", Nat. Mat, 14, 56 ?60 (2015)