Chemistry Reference
In-Depth Information
TABLE 8.2. Foaming Characteristics of Typical Anionic and Nonionic Surfactants
in Distilled Water (Ross-Miles Procedure, at 60
C)
Foam Height
Concentrtation
————————————
Surfactant
(wt%)
Initial
After (min)
C
12
H
25
SO
3
Na
þ
0.25
225
205(1)
C
12
H
25
OSO
3
Na
þ
0.25
220
175(5)
C
14
H
29
SO
3
Na
þ
0.11
240
214(1)
C
14
H
29
OSO
3
Na
þ
0.25
231
184(5)
C
16
H
33
SO
3
K
þ
0.033
245
233(1)
C
16
H
33
SO
3
Na
þ
0.25
245
240(5)
C
18
H
37
OSO
3
Na
þ
0.25
227
227(5)
o-C
8
H
17
C
6
H
4
SO
3
Na
þ
0.15
148
—
p-C
8
H
17
C
6
H
4
SO
3
Na
þ
0.15
134
—
o-C
12
H
25
C
6
H
4
SO
3
Na
þ
0.25
208
—
t-C
9
H
19
C
6
H
4
O(CH
2
CH
2
O)
8
H
0.10
55
45(5)
t-C
9
H
19
C
6
H
4
O(CH
2
CH
2
O)
9
H
0.10
80
60(5)
t-C
9
H
19
C
6
H
4
O(CH
2
CH
2
O)
9
H
0.10
110
80(5)
t-C
9
H
19
C
6
H
4
O(CH
2
CH
2
O)
13
H
0.10
130
110(5)
t-C
9
H
19
C
6
H
4
O(CH
2
CH
2
O)
20
H
0.10
120
110(5)
of surfactants, such as increasing the chain length of an alkyl sulfate, can be
expected to increase its efficiency as a foaming agent. Conversely, branching of
the hydrophobic chain or moving the hydrophilic group to an internal position,
all of which increase the cmc, will usually result in a lower foaming efficiency.
Typical foaming characteristics for several anionic and nonionic surfactants are
given in Table 8.2, where foaming efficiency and persistence were determined
according to the industry-standard Ross-Miles procedure.
The ability of a surfactant to perform as a foaming agent is dependent primarily
on its effectiveness at reducing the surface tension of the solution, its diffusion char-
acteristics, its properties with regard to disjoining pressures in thin films, and the
elastic properties it imparts to interfaces. The amount of foam that can be produced
in a solution under given conditions (i.e., for a set amount of work input) will be
related to the product of the surface tension and the new surface area generated dur-
ing the foaming process [Eq. (8.1)]. Obviously, the lower the surface tension of the
solution, the greater will be the surface area that can be expected to be developed by
the input of a given amount of work. The amount of foam produced by a surfactant
solution is only one part of the foaming story, however. Maintenance of the foam
may be as important as original formation.
It is often observed that the amount of foam produced by the members of a
homologous series of surfactants will go through a maximum as the chain length
of the hydrophobic group increases. This is probably due to the conflicting effects
of the structural changes. In one case, a longer-chain hydrophobe will result in a
