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Séminaires à venir

Materials for Sustainable Growth : OrganoSulfur and Sulfur Hybrids

Kookheon Char The National Creative Research Initiative Center for Intelligent Hybrids The WCU Program of Chemical Convergence for Energy & Environment School of Chemical & Biological Engineering Seoul National University

CHAIRE TOTAL ESPCI Jeudi 4 mai 2017 - 14h00 - Amphi Boreau


With ever-increasing human population, depleting natural resources, and rapid climate change confronting humanity, the role of chemistry is becoming more crucial in addressing these issues and establishing systems for sustainable growth. In this Seminar, recent efforts in our research center (National CRI Center for Intelligent Hybrids), utilizing both organic and inorganic material design and synthesis, to address key issues to such an end are described. As an example, we have established novel chemical methods for the direct utilization of elemental sulfur. More than seven million tons of elemental sulfur are produced in excess each year and are stockpiled in landfill-like deposits in remote areas. While elemental sulfur is known to be environmentally benign and have many interesting physical properties, the shear volume of it left unused is a major emerging issue in the petrochemical industry. Useful conversion of industrial wastes into functional materials, through novel chemistry, for key applications such as Nexgen Li-sulfur batteries and thermal IR imaging will be introduced.

Semiconductor Nanocrystals for Optoelectronics : Shape Matters for the Photon-Electron Interconversions

Kookheon Char The National Creative Research Initiative Center for Intelligent Hybrids The WCU Program of Chemical Convergence for Energy & Environment School of Chemical & Biological Engineering Seoul National University

CHAIRE TOTAL ESPCI Mercredi 10 mai 2017 - 11h00 - Amphi Boreau


Ever since the synthetic methodology to prepare well-defined semiconductor nanocrystals (NCs) is well-established, multilateral efforts have recently emerged to utilize such NCs for optoelectronic devices. The unique optical and electronic properties of the semiconductor NCs serve a novel funtional toolbox which has never been found in conventional technologies and it would contribute to realize more efficient, high-performance, and economic nano- or opto-electronics. To take full advantage of such promising nanomaterials, understanding the fundamental properties of semiconductor NCs along with manipulating them through rational materials design is critically important.

From the viewpoint of materials science, the fundamental design principle of semiconductor NCs and their utilization to electron-photon interconversion devices will be addressed in this presentation. For the efficient electron-to-photon conversion devices, spherical core@shell quantum dots (QDs) have been designed and utilized as the active materials in light emitting diodes (QLEDs). On the basis of the energy-tuned inverted device structure, the core@shell QDs yield color-saturated electroluminescence spectra with high external quantum efficiency and extended device lifetime. For the conversion from photons to electrons, well-defined CdSe tetrapods have been prepared by the continuous precursor injection (CPI) approach. The bicontinuous heterojunction morphology consisting of CdSe tetrapods and conducting polymers produced high photocurrent and power conversion efficiency by the effective dissociation of excitons at the interfaces. The enhancement in the field-effect mobility of CdSe tetrapod networks also suggested that such branced nanocrystals could be one of promising building blocks in hybrid solar cells.

Assembly of optically resonating colloids for the fabrication of metamaterials

Virgine Ponsinet Centre de Recherche Paul Pascal CNRS-Université de Bordeaux

Jeudi 11 mai 2017 - 14h00 - Amphi Boreau


I will present our recent results on the assembly of plasmonic nanoparticles into dense uniform 3D structures, in which tailored localized surface plasmon resonances of the nanoparticles provide specific optical responses. Such self-assembled metamaterials provide a promising platform towards bulk optical materials with unusual effective properties. In particular, we produce lamellar metal-dielectric nanocomposites, which constitute self-assembled hyperbolic metamaterials, and colloidal nanoresonators ("plasmonic raspberries") presenting optical magnetism at visible wavelengths, which can be assembled into a bulk magnetic metamaterial.

Formation and growth of labyrinthine drying patterns in 2-D porous model media

Pascal Panizza Matière Molle, Institut de Physique de Rennes

Jeudi 8 juin - 14h00 - Amphi Boreau


Drying of colloidal solutions in porous media is relevant to many fields such as soil physics, and civil engineering. For all these applications it is essential to understand and to predict the kinetics and topology of the crystal deposits that form during the drying process.
This problem is important for civil engineering owing to salt weathering which damages buildings and other engineering structures and in material science to engineer smart
nanoscale and microscale materials using evaporation as a novel route of controlled selfassembly. Despite the importance of all these applications, this issue still remains elusive notably because of complex couplings between the formation of crystal deposits and the various transport phenomena involved in the drying process which are difficult to unravel.
To address this issue, we investigate drying of colloidal suspensions or surfactant solutions confined in a 2D porous model medium which permits to overcome optical limitation inherent to bulk systems. We observe the formation of thin solid films that interconnect to form a maze structure. Our experiments show that the dynamics of formation of these unusual out of equilibrium patterns is triggered by a regular succession of Haines jumps. We identify the elementary mechanisms leading to the formation of the crystal deposits at the pore scale and then establish a pore-network model that well captures the topology of the labyrinthine structures observed in our experiments as well as their dynamics. Using simple arguments, we predict the topological changes in the drying pattern at the scale of an individual pore that occur when the geometrical parameters of the problem such as the sample thickness and the contact angle that the liquid makes with the substrate are varied. Our experiments confirm our theoretical predictions.

Fluorescent microscopy image of the maze structure observed after the drying of a colloidal suspensions in a 2 D model porous medium made of cylindrical posts whose height and diameter are respectively 30 and 100 micrometers. The interdistance between posts is 175 micrometers