Lyophilic colloidal solutions thermodynamics

Some colloidal systems such as polymer solutions and surfactant solutions containing micelles are thermodynamically stable and form spontaneously. These types of colloids are called lyophilic colloids. However, most systems encountered contain lyophobic colloids (particles insoluble in the solvent). In the preparation of such lyophobic colloidal dispersions, the presence of a stabilizing substance is essential. Because van der Waals forces usually tend to lead to agglomeration (flocculation) of the particles, stability of such colloids requires that the particles repel one another, either by carrying a net electrostatic charge or by being coated with an adsorbed layer of large molecules compatible with the solvent. 

Further removal of the dispersion medium results in a conversion of gel into a solid macroscopic phase, i.e. into the soap crystal. Based on the results of the X-ray diffraction analysis, soap crystals were shown to have a lamellar structure. The surfactant - water system can thus undergo transitions into various states, depending on the content of components from a homogeneous system (surfactant molecular solution) to lyophilic colloidal state and further to macroscopic heterogeneous system (soap crystals in water). Different states of the system can be described by a particular thermodynamic equilibrium, i.e. ... 

The lyophilic colloids mostly behave as true solutions, form spontaneously and are stable thermodynamically. On the other hand, the lyophobic colloids are always unstable thermod)mamically. Despite inherent Instability, many of the lyophobic colloidal systems persist indefinitely. This is attributed to the electrical charge carried by the colloidal system. A detailed discussion of the electrical properties of colloids will be dealt with elsewhere in this chapter. 

It is convenient to classify sols into three types (I) tvophilii (solvent loving) colloids, for example, are solutions or gelatin or starch in water (2 association colloids, of which a solution of Soap in water at moderate concentration is an example and (3) Iwphohic (solvent repelling) colloids, for example, sulfur in water. Both lyophilic and association colloids can be prepared in thermodynamic equilibrium, so that when solvent is removed and then returned to the system, the original properties of the system are regained. 

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