Séminaire Michael Grünwald "Computational self-assembly of nanomaterials..."

Michael Grünwald (University of Utah) présentera le mercredi 13 juin à 14h, dans la salle des Conseils de la faculté de Chimie (T32-42, 1er étage, salle 101), un séminaire intitulé :

Computational self-assembly of nanomaterials - from covalent organic frameworks to nanocrystal superlattices

Abstract

The self-assembly of molecular and supramolecular building blocks into well-ordered structures requires exquisite control over interactions and driving forces. In many cases, the interactions responsible for successful self-assembly are subtle and not easily tuned in experiments. Our group uses molecular modeling and computer simulations to reveal the microscopic details of structure formation and to develop guiding principles for the self-assembly of complex materials. In this talk, I will discuss the self-assembly of ordered structures from very different building blocks : porous crystals made of organic molecules (COFs) and superlattices of colloidal semiconductor nanocrystals covered with organic ligands. In the case of COFs, our simulations show that stacking interactions in solution, typically assumed to be weak, are responsible for the limited crystalline quality of COFS in experiments. In the case of nanocrystal superlattices, I will present a coarse-grained molecular model that is able to reproduce the rich phase behavior found ind experiments, including recently observed superlattices with partial orientational order of nanocrystals.

 Autre séminaire à venir :

Yves Méheust (Université de Rennes) présentera le lundi 9 juillet à 14h, dans la salle des Conseils de la faculté de Chimie (T32-42, 1er étage, salle 101), un séminaire intitulé :

Vapor transport in clay powders : cationic control of normal vs. anomalous diffusion

Abstract

We study diffusive vapor transport through a synthetic fluorohectorite powder, in which water molecules travel in mesopores between the clay grains but can also intercalate inside the nanoporous grains, making them swell. The intercalation dynamics is known to be controlled by the type of cation ; in this case exchanging the cations from Na⁺ to Li⁺ accelerates the intercalation process. By inferring mesoporous humidity profiles from a space-resolved measurement of grain swelling based on X-ray diffraction, and analyzing these profiles in terms of fractional diffusion, we show that exchanging the cations changes mesoporous transport from Fickian to markedly subdiffusive. This behavior results both from a change in the intercalation dynamics, and from the feedback of transport on the medium’s permeability due to grain swelling. An important practical implication is a large difference in the time needed for vapor to permeate a given length of the clay, depending on the type of intercalated cation.