Solid-liquid systems crystalline hydrates

Figure 17 Solid-liquid phase diagram of the system water-ter t-butanol X = mol fraction concentration and P denotes a probable peritectic transition. A.2H2O is a stable crystalline hydrate, with = 0.55°C. The two eutectic points correspond to —8.52°C (x = 0.065) and —4.55°C (x = 0.62). Adapted from Takaizumf ...

The many remarkable physico-chemical properties of aqueous surfactant systems, as well as their numerous practical applications, can be referred to the tendency of the nonpolar groups to avoid contact with water at the same time as the polar part tends to be strongly hydrated. The adsorption of surfactants at interfaces between aqueous solutions and air, another liquid phase or a solid is one consequence of this, the extensive aggregation into various types of large aggregates termed micelles — from lat. micella meaning small bit — and liquid crystalline phases is another. 

A typical and simplified phase diagram for a water-surfactant system is indicated in Fig. 4. The ordinate is the temperature and the abscissa the composition. L indicates the liquid-phase region that may include micellar solutions as well as microemulsions. X indicates the presence of a solid substance that may be the pure surfactant or a stoequio-metric hydrate crystal. The A and B domes are liquid-crystalline regions. 

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