  In this paper we study the main surface characteristics which control the
foamability of solutions of various surfactants. Experiments with anionic,
cationic and nonionic surfactants with different head groups and chain lengths
are performed in a wide concentration range, from 0.001 mM to 100 mM. The
electrolyte concentration is also varied from 0 up to 100 mM. For all
surfactants studied, three regions in the dependence of the foamability, VA, on
the logarithm of surfactant concentration, lgCS, are observed. In Region 1, VA
is very low and depends weakly on CS. In Region 2, VA increases steeply with
CS. In Region 3, VA reaches a plateau. A key new element in our interpretation
of the foaming data is that we use the surface tension measurements to
determine the dependence of the main surface properties (surfactant adsorption,
surface coverage and surface elasticity) on the surface age of the bubbles. In
this way we interpret the results from the foaming tests by considering the
properties of the dynamic adsorption layers, formed during foaming. The data
for the nonionic and ionic surfactants merge around two master curves when
plotted as a function of the surface coverage, the surface mobility factor, or
the Gibbs elasticity of the dynamic adsorption layers. This difference between
the ionic and nonionic surfactants is explained with the important contribution
of the electrostatic repulsion between the foam film surfaces for the ionic
surfactants which stabilizes the dynamic foam films even at moderate surface
coverage and at relatively high ionic strength. In contrast, the films formed
from solutions of nonionic surfactants are stabilized via steric repulsion
which becomes sufficiently high to prevent bubble coalescence only at rather
high surface coverage (> 90 %) which corresponds to related high Gibbs
elasticity (> 150 mN/m) and low surface mobility of the dynamic adsorption
layers.
