The macroscopic behaviour of material systems in which two bulk phases are in contact can only fully be understood if their mutual boundary is invested with distinct physical attributes. Such boundaries are actually thin interfacial regions across which bulk material quantities may undergo great change. For example, liquid-vapour interfaces are typically only 10°A (= 10−9m) thick yet support density changes from 1 to 103 kg m−3. In the case of a fluid-fluid interface between bulk phases which consist of several molecular species, the relative concentrations of individual species within the interface usually differ from those in either bulk phase (a phenomenon termed adsorption). Indeed, very small bulk phase concentrations of certain species may in equilibrium be accompanied by high interfacial concentrations of these species. Such so-called surfactants are responsible for much of the notorious difficulty of obtaining reproducible experimental data for interfaces.
KeywordsEntropy Production Interfacial Region Capillary Wave Balance Relation Notorious Difficulty
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