Mesoscopic phase

In this chapter we have tried to show how a rational addition of nentral additives or ligands complexing with either the inorganic or organic reactants, respectively, can be used to control the mesoscopic phase behavior of inorganic-snrfactant composites. The focns has been on siliceous materials, but the approach is applicable also to the synthesis of nonsiliceous materials. The discnssion has been merely qnalitative in natnre, dne to the partial lack of accurate experimental... 

The increase of the redox potential of a metal cluster in a solvent with its nuclearity is now well established 1-4). The difference between the single atom and the bulk metal potentials is large (more than 2 V, for example, in the case of silver (3)). The size dependence of the redox potential for metal clusters of intermediate nuclearity plays an important role in numerous processes, particularly electron transfer catalysis. Although some values are available for silver clusters (5, 6), the transition of the properties from clusters (mesoscopic phase) to bulk metal (macroscopic phase) is unknown except for the gas phase (7-9). 

The redox potentials of short-lived silver clusters have been determined through kinetics methods using reference systems. Depending on their nuclearity, the clusters change behavior from electron donor to electron acceptor, the threshold being controlled by the reference system potential. Bielectronic systems are often used as electron donors in chemistry. When the process is controlled by critical conditions as for clusters, the successive steps of monoelectronic transfer (and not the overall potential), of which only one determines the threshold of autocatalytical electron transfer (or of development) must be separately considered. The present results provide the nuclearity dependence of the silver cluster redox potential in solution close to the transition between the mesoscopic phase and the bulk metal-like phase. A comparison with other literature data allows emphasis on the influence of strong interaction of the environment (surfactant, ligand, or support) on the cluster redox potential and kinetics. Rela-... 

For more than two decades, extensive research work has been devoted to the unique properties of clusters. They are made of a small number (or nucleaiity) of atoms or molecules only, and therefore constitute a new state of matter, or mesoscopic phase, between the atom or molecule and the crystal. New methods have been developed in physics and chemistry for their synthesis, their direct observation, the study of their properties, and of their crucial role in number of processes, such as phase transition, catalysis, surface phenomena, imaging. Owii to its specific approach, radiation chemistry offei first the opportunity to reveal the existence of nuclearity-dependent properties of clusters and has then proven to be a powerfid method to study the mechanisms of cluster formation and reactivity in solution. 

All diffraction measurements show that a6T is nearly co-planar in crystal powders [16] and even more co-planar in single crystals [48]. Also a mesoscopic phase IS discussed which appears at temperatures above 583 K [49,50]. 

Poly(3-decylthiophene) in crystalline powders has a co-planar structure, but the alkyl-chain planes are not co-planar with the thiophene backbone [89]. This polymer shows a temperature-dependent polymorphism with two crystalline and a (probably nematic) mesoscopic phase [90]. In the mesoscopic phase the side-chains can freely rotate, while the main chains can deviate from planarity. 

Dye-sensitized systems are not suited to interpretation by conventional device physics methods on account of two features firstly, the mesoscopic phase separation of electron and hole conductors, which makes the porous material unable to sustain large electric fields and secondly, the separation, through the use of sensitizers, of optical absorption from charge transport in either material. Efforts to understand the photovoltaic action of the DSSC are leading to a reassessment of basic principles and the possibilities of novel photovoltaic designs. 

We are developing a general purpose method for mesoscale soft-condensed matter computer simulations, based on a functional Langevin approach for mesoscopic phase separation dynamics of complex polymer liquids. This project aims to consider topics of utmost importance in chemical engineering, such as chemical reactions, convection and flow effects, surfaces and boundaries, etc. 

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