Projet ANR-06-BLAN-0144 – HETER-EAU : THE BEHAVIOR OF WATER IN HETEROGENEOUS ENVIRONMENTS
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : ECOLE NATIONALE SUPERIEURE DE CHIMIE DE PARIS (ECOLE NATIONALE SUPERIEURE DE CHIMIE DE PARIS)
Partenaires : Centre national de la recherche scientifique; École nationale supérieure de chimie de Paris; École nationale supérieure de chimie de Paris; Université de Haute-Alsace
Montant : 432000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : THE BEHAVIOR OF WATER IN HETEROGENEOUS CONFINED ENVIRONMENTS  B.1. Aim and scope of the project  There are many intriguing situations in everyday life where water is confined to spaces of nanoscopic dimensions. Examples include protein cavities [1], ion channels [2], colloidal assemblies [3,4], microfluidic devices [5], zeolites and other open-framework inorganic materials [6,7]. Fundamental interest stems from the fact that the properties of confined water are believed to be very different from those of the corresponding bulk fluid at the same temperature and chemical potential [8-12]. From a practical point of view, confined water plays a key role in many applications such as heterogeneous catalysis, ion-exchange and separation.  	The behavior of water close to a hydrophobic surface has been (and is still) the subject of numerous studies. When two such surfaces approach each other, a possible transition was predicted, at small enough separations, from the confined water film to the vapor phase (the so-called "drying" transition) [3,4,7,8,13]. It was also suggested that the experimentally observed long-range attraction between hydrophobic surfaces might arise from the growth and bridging of small vapor bubbles between the surfaces. But it is not yet clear from the experiments whether hydrophobic hydration leads to the formation of a thin layer of low-density (depleted) water close to the surface, or of a truly heterogeneous fluid containing vapor microbubbles.  Understanding the behavior of nano-confined water is relevant to such important problems as protein stability. Since the well-known paper by Kauzmann, in the late 1950's [14], it is generally believed that hydrophobic interaction is an important driving force for (globular) proteins folding [15-18]. Yet subsequent attempts to quantify this phenomenon, using the simple hydrophobic interaction model have not been successful [19]. It seems clear that the so-called "hydrophobic residues" cannot be simply modeled as purely hydrophobic hard walls. A protein surface should rather be viewed as a chemically heterogeneous system.  The need to understand the behavior of water close to complex, heterogeneous surfaces also exists in many applications such as molecular separations (molecular sieving). An example of this kind is the organic solvent separation from moist gas stream, using aluminosilicate zeolites or activated carbon [20]. Pure graphitic carbon is supposedly hydrophobic, but activated carbon materials contain, in some proportion, hydrophilic polar groups, which are presumably responsible for a reduced effectiveness of activated carbon filters in presence of water.   This general goal of this project is to better understand the structure and thermodynamics of water in heterogeneous confined environments. For this, we have selected a range of nano-porous silica and carbon materials (with controlled porosity) that will be used for investigating the behavior of confined water. Pure silica is believed to be a highly non wetting surface for water (contact angle of ~120°), while carbon has an intermediate wetting-non wetting behavior (contact angle of ~90°). A joint experimental and theoretical (modeling) effort will be carried out in order to describe in details the condensation mechanism and the structure of water confined in a mixed hydrophobic/hydrophilic porous volumes (from the all silica hydrophobic to the partially hydrophobic nanoporous carbon counterpart). Among the issues to be addressed, we will focus our attention on the characteristic length of water condensation around the hydrophilic defects placed on an overall hydrophobic surface, the effect of the pattern distribution of these defects and of the geometry (pore shape and widths) of the confining media on the water condensation/drying process.   Partner 2 (J.Patarin group in Mulhouse) will perform the synthesis and characterization of hydrophobic all-silica zeolites of various types, as well as their partly h