Interfacial Phenomena and Data

An illustrative explanation of the interfacial tension a is the effort of reversible energy that is needed in order to create new interface between two phases. 

A usual interpretation from mechanics is the work of creating new surface area by moving molecules from the bulk phase to the interface, whereas the thermodynamic interpretation is a change of inner energy when the surface area is altered. 

Including the finite interface as a further phase into the fundamental equation of thermodynamics for the free energy F and the free enthalpy G [12], 

Equation (2.5) explains the temperature dependency of the interfadal tension as the change in entropy during the formation of surface. Increasing temperatures are combined with rising mobility of molecules. Thus, the work of forming new surface area becomes lower and the interfadal tension is decreased at elevated process temperatures. 

On the contrary, the interfadal tension between fluid phases usually decreases at higher process pressures. This reveals an attractive feature for spray processes at high pressures [13]. Following Eq. (2.6), this means an enhancement of molecule concentration within the interfacial volume (adsorption) and in summary a volume decrease of the total system at constant pressure appears. 

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