Projet ANR-07-JCJC-0023 – PACTIS : PArticles in Complex fluids : Transition-Induced Structures
Programme : Jeunes chercheuses & jeunes chercheurs (JCJC) 2007
Année de financement : 2007
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION  AQUITAINE LIMOUSIN (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION  AQUITAINE LIMOUSIN)
Partenaires : Centre national de la recherche scientifique
Montant : 150000.0 euros
Date de début : 2007
Durée : 48 mois
Résumé : "Understanding and controlling the organization of colloidal particles in a fluid is a challenge that would allow for the preparation of new materials with various structures and functionalities. Indeed, the wide diversity of geometries that can be produced in soft matter systems (nematic, cubic, hexagonal, lamellar, bicontinuous, etc...) combined to the richness of the properties (optical, chemical, mechanical, electronical) associated with solid colloidal particles, should in principle yield to a huge variety of applications in many different fields. -  Within this context, the objective of our study is to understand and control the structuration of colloidal particles using liquid crystals and phase separating binary fluids. Among the different possible ways to achieve such a goal, we have identified two promising routes that we would like to investigate in detail throughout this project. -  The first one consists in using liquid crystal fields to spatially order colloidal particles. This area has already been the subject of intense research in the past few years and many decisive results, both experimental and theoretical, were obtained by different groups around the world. However, very few studies have focused on the pre-transitional ordering that can occur when colloidal particles are embedded in the isotropic phase of a mesogenic compound close to a liquid crystal phase transition. In such areas, theory and numerical simulations predict the existence of strong pre-transitional effects, such as pre-wetting, that lead to peculiar organizations of the immersed colloids. Evidences for such pre-transitional phenomena were observed in preliminary experiments performed in our laboratory. These results provide us with a strong motivation to carry on our investigation in this area. Furthermore, as we further describe in the next section, we wish to examine in a systematic way the influence of particles shape on the observed structurations, for both pre-transitional studies as well as when the particles are included in a LC phase. The latter situation can be seen as a useful extension to the already extensive literature dealing with spherical objects. Indeed, anisotropic particles may present specific behaviour in organized fluids as well as enhanced interesting properties (conduction, mechanical properties, etc.). -  The second possible route emphasizes the use of phase separating fluids to structure and organize colloidal particles in original transient structures. If many earlier studies have been devoted to phase separation processes, much fewer have focused on the use of such transitions to organize spherical colloids and, as far as we know, almost no experiments have been reported on binary systems containing anisotropic particles. Nevertheless, some numerical simulations pointed out the existence of some original bicontinuous anisotropic morphologies whilst addressing such issues. Following this approach, we have recently identified an experimental system in which such anisotropic transient patterns were obtained in the vicinity of a phase transition line. Details of our preliminary results and experimental system will be given in section B.II.2. The latter will serve as a strong reliable starting basis for our investigation in this area. -  -  As a summary, this project will focus on the following points : -  -  1. Pre-transitional effects and inclusions of anisotropic particles in liquid crystalline phases -  The main objectives are : -  (i)	elucidate the effects found in pre-transitional situations, where little has been shown yet -  (ii)	increase the richness of structure formation and enhance their efficiency in terms of materials synthesis by using anisotropic particles -  2. Structuration of anisotropic particles using phase separating binary fluids. -  -  In conclusion, the present project targets ambitious objectives which range from the discovery and characterization of new structures when nano- and/or micro-ani