Contact interactions thermodynamic factor

A distinctive feature of using weak, non-covalent forces, or for that matter metal-donor bonds, in molecular assemblies is that such interactions are normally readily reversible so that the final product is in thermodynamic equilibrium with its components (usually via its corresponding partially assembled intermediates). This leads to an additional property of most supramolecular systems they have an in-built capacity for error correction not normally available to fully covalent systems. Such a property is clearly of major importance for natural systems with their multitude of intermolecular contacts. It is a factor that will assume increasing importance for the construction of the new (larger) synthetic systems mentioned previously - as both the number of intermolecular contacts present and overall structural complexity are increased. 

The forces of interaction (i.e., prior to contact) which a single, gas-borne particle can be subject to are treated from the perspective of its chemical and physical structure. To provide the requisite perspective for understanding the importance of these compositionally dependent factors, the role of the gas is discussed. Classical electrostatic and multipolar forces and the thermodynamic setting for any interaction involving a particle are described briefly. Principle emphasis in the chapter is given to the van der Waals forces. The modern (Lifshitz) theory is introduced and its relation to the classical Hamaker theory is described. A qualitative discussion of the computational approaches commonly used and experimental evidence for the theory are given. Inclusion of the chemical and physical factors necessary for treatment of cases that arise in actual application of the general theory is discussed. 

In fact, the support surface is not inert. The oxide/water system is thermodynamically metastable and a realistic description of its interface should take into account the oxide hydration and its possible dissolution. The kinetic factor, which is often overlooked for the two types of interactions described above, is here a parameter of prime importance, because the transformations involving the support are far from being instantaneous and should be favored by a long contact time between support and impregnation solution ( aging ). 

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