Physical-Chemical Phenomena at Interfaces

Before turning to a discussion on particular interactions, it is worth reviewing the basic principles of the thermodynamics of surface forces and the concept of surface (or interfadal) free energy and of surface tension in particular. 

FIG U RE 1.1 Schematic illustration of Dupre s experiment, which helps to und tand the concept of surface tension. 

FIGURE 1.2 The thermodynamic definition of the surface free energy according to Gibbs. 

Typically, when far away from the critical conditions, 6 is on the order of interatomic (intermolecu-lar) distances, b, that is, on the order of angstroms (1 A = 10 ° m). As the system nears its critical point corresponding to the complete miscibility or complete mutual solubility of the constituent phases, the value of 5 may reach hundreds or thousands of angstroms. 

Gibbs s approach to the determination of a is valid for any interface liquid/gas (L/G), liquid/ liquid (L1/L2), solid/gas (S/G), solid/liquid (S/L), or solid/solid (S1/S2). The methods are used to either measure or indirectly estimate the interfacial free energy, which may vary significantly depending on the type of interface [3,5]. 

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