Emulsions, Microemulsions, and Lyotropic Liquid Crystals - Surface and Colloid Chemistry: Principles and Applications - page 173

9 Emulsions,

Microemulsions, and
Lyotropic Liquid Crystals

9.1 IntroductIon
In this chapter, special application of surface chemistry principles pertaining to the
oil and water phases will be considered. Oil and water do not mix if shaken. As is
well known, if one shakes oil and water, oil breaks up into small drops (of about a
few millimeters in diameter), but these drops join together rather quickly to return to
their original state (as shown here).

Step I: Oil phase and water phase
Step II: Mixing
Step III: Oil drops in water phase
Step IV: After a short interval
Step V: Oil phase and water phase

However, oil and water can be dispersed with the help of suitable emulsifiers (sur-
factants) to give emulsions (Sjoblom et al., 2008; Birdi, 2008). This is a well-known
fact with emulsions found in the home, such as mayonnaise, the basic reason being
that the interfacial tension (IFT) between oil and water is around 50 mN/m, which
is high, and which leads to the formation of large oil drops. On the other hand, the
addition of suitable emulsifiers reduces IFT to very low values (even much less than
1 mN/m). Emulsion formation means that oil drops remain dispersed for a given
length of time (even up to many years). The stability and the characteristics of these
emulsions are related to the areas of their applications.
Emulsions are mixture of two (or more) immiscible substances. Everyday common
examples are milk, butter (fats, water, salts), margarine, mayonnaise , skin creams, and
others. In butter and margarine, the continuous phase consists of lipids. These lipids
surround the water droplets (water-in-oil emulsion). All technical emulsions are pre-
pared by some kind of mechanical agitation or mixing. Remarkably, the natural prod-
uct, milk, is made by organisms without any agitation inside the mammary glands.
Emulsions are one of the most important application areas of surface-active com-
pounds, and are generally described as belonging to three different kinds:

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