New development in surface forces

The main characteristic of the stability of bubble-particle aggregates is the contact angle v /. The equation 

As a result, the equilibrium contact angle 6 may be calculated from the known equation of Frumkin-Derjaguin s theory (Frumkin 1938, Derjaguin 1940), 

The isotherm FI(h) can be obtained experimentally or calculated on the basis of the surface forces theory. When using Eq. (10D.2) for wetting films of water or aqueous solutions, it is necessary to take into account at least three components of the disjoining pressure, i.e. the dispersion, electrostatic. If, and structural, If, contributions. 

let us consider the influence of the electrostatic potentials of the bubble and particle vj/p on the contact angle in absence of the structural component of the disjoining pressure. We denote by O, the larger potential between 1)/ and v /p, and by Oj the smaller one. 

When the potentials and Oj have the same sign but different orders of magnitude, as is the case for wetting films of water on silica, at some critical thickness the electrostatic forces change from repulsion at h h, to attraction at h h, (Derjaguin et al. 1987), 

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