Interfacial chemistry, clays

In the face of all wisdom concerning choice of models, the section on active centers takes clay as a model, the mineral class that is most, rather than least, complex. Clays happen to be the mineral class most studied with respect to natural reactivity. They are among the more important classes of minerals reactive in natural systems, and they are known to include most of the generic site types thought to be influential in mineral interfacial chemistry. A special emphasis is placed on acidic and oxidizing entities because of their importance and because evidence is accumulating to indicate that they are interrelated. 

Tarapow et al. [83] studied the influence of clay surface chemistry and the processing conditions on the structure and mechanical properties of PP-clay nanocomposites prepared by a melt mixing process. They observed that although the Young s modulus improved with unmodifled clay incorporation, the tensile strength and the impact toughness values decreased. These results were attributed to a poor interfacial adhesion between PP matrix and unmodifled clay. 

Improvements in the application properties of films prepared from nanocomposite latexes are sought. The exfoliation state of the clay (more exfoliated means a larger interfacial area) and the chemistry between the surface of the clay platelets and the polymer matrix are the key parameters to achieve a significant enhancement of the final properties. Samakande et stated that the use of simple organic cations in the modification of clay layers and the subsequent use of the modified clays in the preparation of nanocomposites results in polymeric nanocomposites with only moderately enhanced properties (e.g. thermomechanical). They concluded that for exceptional property enhancement, functional or reactive surfactants are required, in order to compatibilize both phases further. 

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