Collision and Attachment Interactions of Single Air Bubbles with Flat Surfaces in Aqueous Solutions - Drops and Bubbles in Contact with Solid Surfaces - page 230

Figure 11. Influence of surfactant on the lifetime and rupture of wetting films on hydrophobised silica
with a contact angle of 90 ◦ . The maximum lifetime without SDS is 3 s. Addition of 1 10 − 5 × MSDS

increases the lifetime of the wetting film up to 300 s [70].

face plays a critical role in film drainage. Although most of both theoretical and
experimental results are primarily related to the foam films that form between gas
bubbles, in many respects they can be principally generalised for wetting films [43].
The results indicated that the film drainage in the presence of surfactants criti-
cally depends on two factors:

• The film radius which increases the thickness inhomogeneities and the film

drainage rate. The formation of thickness inhomogeneity starts at a film radius
of about 50 micron [61].

• The Gibbs elasticity, E G , which controls the film surface mobility. It expresses

the resistance of the film to local deformation. Films become practically rigid
(non-deformable) at E G =

1mN/m.

The effect of surfactant adsorption on foam film drainage can be adequately de-
scribed by a number of models [30]: the model of Scheludko [65], the model of
Radoev, Dimitov and Ivanov [60], the model of Ruckenstein and Sharma [63] and
the model of Manev, Tsekov and Radoev [42]. However, the model description for
the drainage of wetting films in the presence of surfactants is very limited. Nonethe-
less, Tsekov et al. [72] explained the deviation of wetting film drainage from the