aqueous phase and turn it into a microemulsion. In fact, a complex
equilibrium is established between the oil phase, a monolayer at the oilwater interface, and the aqueous micellar solution. It is also possible for
reverse microemulsion aggregates to be present in the oil phase.
Oil–water
interface
Aqueous phase
Oil phase
Figure 7.15 When an aqueous surfactant phase above its CMC is brought in
contact with a pure oil phase, the micelles are able to solubilize small oil droplets. The
aqueous phase is a microemulsion. A monolayer of the surfactant likely populates
the oil–water interface. The diagram also shows a “reverse” micelle in the oil phase
containing a water droplet.
Table 7.2
The CMC Values of Various Surfactants
Surfactant
CMC (mol dm
–3 )
Dodecylammonium chloride
1.47 × 10
–2
Dodecyltrimethylammonium bromide
1.56 × 10
–2
Decyltrimethylammonium bromide
6.5 × 10
–2
Sodium dodecyl sulfate
8.3 × 10
–3
Sodium tetradecyl sulfate
2.1 × 10
–3
Sodium decyl sulfate
3.3 × 10
–2
Sodium octyl sulfate
1.33 × 10
–1
CH 3 (CH 2 ) 9 (OCH 2 CH) 6 OH
3 × 10
–4
CH 3 (CH 2 ) 9 (OCH 2 CH) 9 OH
1.3 × 10
–3
CH 3 (CH 2 ) 11 (OCH 2 CH) 6 OH
8.7 × 10
–5
CH 3 (CH 2 ) 7 C 6 H 4 (OCH 2 CH) 6 OH
2.05 × 10
–4
Source: Holmberg, K., Jönsson, B., Kronberg, B., Lindman, B. 2003.
Surfactants and Polymers in Aqueous Solution, 2nd ed.,
John Wiley & Sons, Chichester, West Sussex, England. With
permission.
SURFACTANT CHEMISTRY 245