WA, USA), where three parameters were defined: hmax, the maximum
thickness of the drainage; the exponent m; and t1/2, the time
required to attain half the maximum thickness of the drainage
(Raharitsifa et al., 2006).
h ¼ ðhmaxt
mÞ=ðt
m
1=2 þ t
mÞ ð3Þ
Normally, drainage is high at the beginning but slows down
over time, characterized by a sigmoid curve, where m values are
close to 1. When drainage curves became more sigmoidal, m values
increased up to 3 or higher. Foam stability is expected to increase
as the hmax decreases; t1/2 is equivalent to half-life.
Ostwald ripening kinetics was calculated based on the percent
of the backscattering medium values, taken as a function of time,
and fitted to a linear model. In this case, the slope corresponds to
the rate of the increase of bubble diameter.